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• F# Objects &ndash; Integration with the other .Net Languages &ndash; Part 2

  - by MarkPearl

  So in part one of my posting I covered the real basics of object creation. Today I will hopefully dig a little deeper… My expert F# book brings up an interesting point – properties in F# are just syntactic sugar for method calls. This makes sense… for instance assume I had the following object with the property exposed called Firstname. type Person(Firstname : string, Lastname : string) = member v.Firstname = Firstname I could extend the Firstname property with the following code and everything would be hunky dory… type Person(Firstname : string, Lastname : string) = member v.Firstname = Console.WriteLine("Side Effect") Firstname   All that this would do is each time I use the property Firstname, I would see the side effect printed to the screen saying “Side Effect”. Member methods have a very similar look & feel to properties, in fact the only difference really is that you declare that parameters are being passed in. type Person(Firstname : string, Lastname : string) = member v.FullName(middleName) = Firstname + " " + middleName + " " + Lastname   In the code above, FullName requires the parameter middleName, and if viewed from another project in C# would show as a method and not a property. Precomputation Optimizations Okay, so something that is obvious once you think of it but that poses an interesting side effect of mutable value holders is pre-computation of results. All it is, is a slight difference in code but can result in quite a huge saving in performance. Basically pre-computation means you would not need to compute a value every time a method is called – but could perform the computation at the creation of the object (I hope I have got it right). In a way I battle to differentiate this from lazy evaluation but I will show an example to explain the principle. Let me try and show an example to illustrate the principle… assume the following F# module namespace myNamespace open System module myMod = let Add val1 val2 = Console.WriteLine("Compute") val1 + val2 type MathPrecompute(val1 : int, val2 : int) = let precomputedsum = Add val1 val2 member v.Sum = precomputedsum type MathNormalCompute(val1 : int, val2 : int) = member v.Sum = Add val1 val2 Now assume you have a C# console app that makes use of the objects with code similar to the following… using System; using myNamespace; namespace CSharpTest { class Program { static void Main(string[] args) { Console.WriteLine("Constructing Objects"); var myObj1 = new myMod.MathNormalCompute(10, 11); var myObj2 = new myMod.MathPrecompute(10, 11); Console.WriteLine(""); Console.WriteLine("Normal Compute Sum..."); Console.WriteLine(myObj1.Sum); Console.WriteLine(myObj1.Sum); Console.WriteLine(myObj1.Sum); Console.WriteLine(""); Console.WriteLine("Pre Compute Sum..."); Console.WriteLine(myObj2.Sum); Console.WriteLine(myObj2.Sum); Console.WriteLine(myObj2.Sum); Console.ReadKey(); } } } The output when running the console application would be as follows…. You will notice with the normal compute object that the system would call the Add function every time the method was called. With the Precompute object it only called the compute method when the object was created. Subtle, but something that could lead to major performance benefits. So… this post has gone off in a slight tangent but still related to F# objects.

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• Reading graph inputs for a programming puzzle and then solving it

  - by Vrashabh

  I just took a programming competition question and I absolutely bombed it. I had trouble right at the beginning itself from reading the input set. The question was basically a variant of this puzzle http://codercharts.com/puzzle/evacuation-plan but also had an hour component in the first line(say 3 hours after start of evacuation). It reads like this This puzzle is a tribute to all the people who suffered from the earthquake in Japan. The goal of this puzzle is, given a network of road and locations, to determine the maximum number of people that can be evacuated. The people must be evacuated from evacuation points to rescue points. The list of road and the number of people they can carry per hour is provided. Input Specifications Your program must accept one and only one command line argument: the input file. The input file is formatted as follows: the first line contains 4 integers n r s t n is the number of locations (each location is given by a number from 0 to n-1) r is the number of roads s is the number of locations to be evacuated from (evacuation points) t is the number of locations where people must be evacuated to (rescue points) the second line contains s integers giving the locations of the evacuation points the third line contains t integers giving the locations of the rescue points the r following lines contain to the road definitions. Each road is defined by 3 integers l1 l2 width where l1 and l2 are the locations connected by the road (roads are one-way) and width is the number of people per hour that can fit on the road Now look at the sample input set 5 5 1 2 3 0 3 4 0 1 10 0 2 5 1 2 4 1 3 5 2 4 10 The 3 in the first line is the additional component and is defined as the number of hours since the resuce has started which is 3 in this case. Now my solution was to use Dijisktras algorithm to find the shortest path between each of the rescue and evac nodes. Now my problem started with how to read the input set. I read the first line in python and stored the values in variables. But then I did not know how to store the values of the distance between the nodes and what DS to use and how to input it to say a standard implementation of dijikstras algorithm. So my question is two fold 1.) How do I take the input of such problems? - I have faced this problem in quite a few competitions recently and I hope I can get a simple code snippet or an explanation in java or python to read the data input set in such a way that I can input it as a graph to graph algorithms like dijikstra and floyd/warshall. Also a solution to the above problem would also help. 2.) How to solve this puzzle? My algorithm was: Find shortest path between evac points (in the above example it is 14 from 0 to 3) Multiply it by number of hours to get maximal number of saves Also the answer given for the variant for the input set was 24 which I dont understand. Can someone explain that also. UPDATE: I get how the answer is 14 in the given problem link - it seems to be just the shortest path between node 0 and 3. But with the 3 hour component how is the answer 24 UPDATE I get how it is 24 - its a complete graph traversal at every hour and this is how I solve it Hour 1 Node 0 to Node 1 - 10 people Node 0 to Node 2- 5 people TotalRescueCount=0 Node 1=10 Node 2= 5 Hour 2 Node 1 to Node 3 = 5(Rescued) Node 2 to Node 4 = 5(Rescued) Node 0 to Node 1 = 10 Node 0 to Node 2 = 5 Node 1 to Node 2 = 4 TotalRescueCount = 10 Node 1 = 10 Node 2= 5+4 = 9 Hour 3 Node 1 to Node 3 = 5(Rescued) Node 2 to Node 4 = 5+4 = 9(Rescued) TotalRescueCount = 9+5+10 = 24 It hard enough for this case , for multiple evac and rescue points how in the world would I write a pgm for this ?

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• Why is 0 false?

  - by Morwenn

  This question may sound dumb, but why does 0 evaluates to false and any other [integer] value to true is most of programming languages? String comparison Since the question seems a little bit too simple, I will explain myself a little bit more: first of all, it may seem evident to any programmer, but why wouldn't there be a programming language - there may actually be, but not any I used - where 0 evaluates to true and all the other [integer] values to false? That one remark may seem random, but I have a few examples where it may have been a good idea. First of all, let's take the example of strings three-way comparison, I will take C's strcmp as example: any programmer trying C as his first language may be tempted to write the following code: if (strcmp(str1, str2)) { // Do something... } Since strcmp returns 0 which evaluates to false when the strings are equal, what the beginning programmer tried to do fails miserably and he generally does not understand why at first. Had 0 evaluated to true instead, this function could have been used in its most simple expression - the one above - when comparing for equality, and the proper checks for -1 and 1 would have been done only when needed. We would have considered the return type as bool (in our minds I mean) most of the time. Moreover, let's introduce a new type, sign, that just takes values -1, 0 and 1. That can be pretty handy. Imagine there is a spaceship operator in C++ and we want it for std::string (well, there already is the compare function, but spaceship operator is more fun). The declaration would currently be the following one: sign operator<=>(const std::string& lhs, const std::string& rhs); Had 0 been evaluated to true, the spaceship operator wouldn't even exist, and we could have declared operator== that way: sign operator==(const std::string& lhs, const std::string& rhs); This operator== would have handled three-way comparison at once, and could still be used to perform the following check while still being able to check which string is lexicographically superior to the other when needed: if (str1 == str2) { // Do something... } Old errors handling We now have exceptions, so this part only applies to the old languages where no such thing exist (C for example). If we look at C's standard library (and POSIX one too), we can see for sure that maaaaany functions return 0 when successful and any integer otherwise. I have sadly seen some people do this kind of things: #define TRUE 0 // ... if (some_function() == TRUE) { // Here, TRUE would mean success... // Do something } If we think about how we think in programming, we often have the following reasoning pattern: Do something Did it work? Yes -> That's ok, one case to handle No -> Why? Many cases to handle If we think about it again, it would have made sense to put the only neutral value, 0, to yes (and that's how C's functions work), while all the other values can be there to solve the many cases of the no. However, in all the programming languages I know (except maybe some experimental esotheric languages), that yes evaluates to false in an if condition, while all the no cases evaluate to true. There are many situations when "it works" represents one case while "it does not work" represents many probable causes. If we think about it that way, having 0 evaluate to true and the rest to false would have made much more sense. Conclusion My conclusion is essentially my original question: why did we design languages where 0 is false and the other values are true, taking in account my few examples above and maybe some more I did not think of? Follow-up: It's nice to see there are many answers with many ideas and as many possible reasons for it to be like that. I love how passionate you seem to be about it. I originaly asked this question out of boredom, but since you seem so passionate, I decided to go a little further and ask about the rationale behind the Boolean choice for 0 and 1 on Math.SE :)

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• I thought the new AUTO_SAMPLE_SIZE in Oracle Database 11g looked at all the rows in a table so why do I see a very small sample size on some tables?

  - by Maria Colgan

  I recently got asked this question and thought it was worth a quick blog post to explain in a little more detail what is going on with the new AUTO_SAMPLE_SIZE in Oracle Database 11g and what you should expect to see in the dictionary views. Let’s take the SH.CUSTOMERS table as an example.  There are 55,500 rows in the SH.CUSTOMERS tables. If we gather statistics on the SH.CUSTOMERS using the new AUTO_SAMPLE_SIZE but without collecting histogram we can check what sample size was used by looking in the USER_TABLES and USER_TAB_COL_STATISTICS dictionary views. The sample sized shown in the USER_TABLES is 55,500 rows or the entire table as expected. In USER_TAB_COL_STATISTICS most columns show 55,500 rows as the sample size except for four columns (CUST_SRC_ID, CUST_EFF_TO, CUST_MARTIAL_STATUS, CUST_INCOME_LEVEL ). The CUST_SRC_ID and CUST_EFF_TO columns have no sample size listed because there are only NULL values in these columns and the statistics gathering procedure skips NULL values. The CUST_MARTIAL_STATUS (38,072) and the CUST_INCOME_LEVEL (55,459) columns show less than 55,500 rows as their sample size because of the presence of NULL values in these columns. In the SH.CUSTOMERS table 17,428 rows have a NULL as the value for CUST_MARTIAL_STATUS column (17428+38072 = 55500), while 41 rows have a NULL values for the CUST_INCOME_LEVEL column (41+55459 = 55500). So we can confirm that the new AUTO_SAMPLE_SIZE algorithm will use all non-NULL values when gathering basic table and column level statistics. Now we have clear understanding of what sample size to expect lets include histogram creation as part of the statistics gathering. Again we can look in the USER_TABLES and USER_TAB_COL_STATISTICS dictionary views to find the sample size used. The sample size seen in USER_TABLES is 55,500 rows but if we look at the column statistics we see that it is same as in previous case except  for columns  CUST_POSTAL_CODE and  CUST_CITY_ID. You will also notice that these columns now have histograms created on them. The sample size shown for these columns is not the sample size used to gather the basic column statistics. AUTO_SAMPLE_SIZE still uses all the rows in the table - the NULL rows to gather the basic column statistics (55,500 rows in this case). The size shown is the sample size used to create the histogram on the column. When we create a histogram we try to build it on a sample that has approximately 5,500 non-null values for the column.  Typically all of the histograms required for a table are built from the same sample. In our example the histograms created on CUST_POSTAL_CODE and the CUST_CITY_ID were built on a single sample of ~5,500 (5,450 rows) as these columns contained only non-null values. However, if one or more of the columns that requires a histogram has null values then the sample size maybe increased in order to achieve a sample of 5,500 non-null values for those columns. n addition, if the difference between the number of nulls in the columns varies greatly, we may create multiple samples, one for the columns that have a low number of null values and one for the columns with a high number of null values.  This scheme enables us to get close to 5,500 non-null values for each column. +Maria Colgan

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• ?12c database ????Adaptive Execution Plans ????????

  - by Liu Maclean(???)

  12c R1 ????SQL??????- Adaptive Execution Plans ????????,???????optimizer ??????(runtime)???????????????, ????????????????????? SQL???????? ????????????, ?????????????????????????????????????????????????????????????adaptive plan ????????????????????????????????????,?????subplan???????????????????? ??????, ???????? ???????????????,?????????, ?????? ???????????????”???”????, ???????????????????buffer ???????  ????????????,?????,??????????????????? ???optimizer ?????????????????????????,?????????????????????????????????????????plan???? ??12C?????????????, ???????????????????,?????? ???????????? ????????????2???: Dynamic Plans????: ???????????????????????;??????,???optimizer??????????subplans??????????????, ???????????????????,?????????????? Reoptimization????: ?Dynamic Plans????,Reoptimization??????????????????????Reoptimization??,?????????????????????????,??reoptimization????? OPTIMIZER_ADAPTIVE_REPORTING_ONLY ???? report-only????????????????TRUE,?????????report-only????,???????????????,??????????????? Dynamic Plans ??????????????,????????????????????????, ?????????????,???????????,????????????????????????????????????????? ?????????????final plan??????????????default plan, ??final plan?default plan???????,????????????? subplan ???????????????,???????????????????????? ??????,???????statistics collector ?buffer???????????statistics collector?????????????????,???????????????????????????? ?????????????????????????????????????????,??????????,?????????????? ???????????,???????buffer???? ???????????????,?????????????????????????????,??????buffer,??????final plan? ????????,???????????????????????,????????????????? ?V$SQL??????IS_RESOLVED_DYNAMIC_PLAN??????????final plan???default plan? ??????dynamic plan ???????SQL PLAN directives?????? declare cursor PLAN_DIRECTIVE_IDS is select directive_id from DBA_SQL_PLAN_DIRECTIVES; begin for z in PLAN_DIRECTIVE_IDS loop DBMS_SPD.DROP_SQL_PLAN_DIRECTIVE(z.directive_id); end loop; end; / explain plan for select /*MALCEAN*/ product_name from oe.order_items o, oe.product_information p where o.unit_price=15 and quantity>1 and p.product_id=o.product_id; select * from table(dbms_xplan.display()); Plan hash value: 1255158658 www.askmaclean.com ------------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 4 | 128 | 7 (0)| 00:00:01 | | 1 | NESTED LOOPS | | | | | | | 2 | NESTED LOOPS | | 4 | 128 | 7 (0)| 00:00:01 | |* 3 | TABLE ACCESS FULL | ORDER_ITEMS | 4 | 48 | 3 (0)| 00:00:01 | |* 4 | INDEX UNIQUE SCAN | PRODUCT_INFORMATION_PK | 1 | | 0 (0)| 00:00:01 | | 5 | TABLE ACCESS BY INDEX ROWID| PRODUCT_INFORMATION | 1 | 20 | 1 (0)| 00:00:01 | ------------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 3 - filter("O"."UNIT_PRICE"=15 AND "QUANTITY">1) 4 - access("P"."PRODUCT_ID"="O"."PRODUCT_ID") alter session set events '10053 trace name context forever,level 1'; OR alter session set events 'trace[SQL_Plan_Directive] disk highest'; select /*MALCEAN*/ product_name from oe.order_items o, oe.product_information p where o.unit_price=15 and quantity>1 and p.product_id=o.product_id; ---------------------------------------------------------------+-----------------------------------+ | Id | Operation | Name | Rows | Bytes | Cost | Time | ---------------------------------------------------------------+-----------------------------------+ | 0 | SELECT STATEMENT | | | | 7 | | | 1 | HASH JOIN | | 4 | 128 | 7 | 00:00:01 | | 2 | NESTED LOOPS | | | | | | | 3 | NESTED LOOPS | | 4 | 128 | 7 | 00:00:01 | | 4 | STATISTICS COLLECTOR | | | | | | | 5 | TABLE ACCESS FULL | ORDER_ITEMS | 4 | 48 | 3 | 00:00:01 | | 6 | INDEX UNIQUE SCAN | PRODUCT_INFORMATION_PK| 1 | | 0 | | | 7 | TABLE ACCESS BY INDEX ROWID | PRODUCT_INFORMATION | 1 | 20 | 1 | 00:00:01 | | 8 | TABLE ACCESS FULL | PRODUCT_INFORMATION | 1 | 20 | 1 | 00:00:01 | ---------------------------------------------------------------+-----------------------------------+ Predicate Information: ---------------------- 1 - access("P"."PRODUCT_ID"="O"."PRODUCT_ID") 5 - filter(("O"."UNIT_PRICE"=15 AND "QUANTITY">1)) 6 - access("P"."PRODUCT_ID"="O"."PRODUCT_ID") ===================================== SPD: BEGIN context at statement level ===================================== Stmt: ******* UNPARSED QUERY IS ******* SELECT /*+ OPT_ESTIMATE (@"SEL$1" JOIN ("P"@"SEL$1" "O"@"SEL$1") ROWS=13.000000 ) OPT_ESTIMATE (@"SEL$1" TABLE "O"@"SEL$1" ROWS=13.000000 ) */ "P"."PRODUCT_NAME" "PRODUCT_NAME" FROM "OE"."ORDER_ITEMS" "O","OE"."PRODUCT_INFORMATION" "P" WHERE "O"."UNIT_PRICE"=15 AND "O"."QUANTITY">1 AND "P"."PRODUCT_ID"="O"."PRODUCT_ID" Objects referenced in the statement PRODUCT_INFORMATION[P] 92194, type = 1 ORDER_ITEMS[O] 92197, type = 1 Objects in the hash table Hash table Object 92197, type = 1, ownerid = 6573730143572393221: No Dynamic Sampling Directives for the object Hash table Object 92194, type = 1, ownerid = 17822962561575639002: No Dynamic Sampling Directives for the object Return code in qosdInitDirCtx: ENBLD =================================== SPD: END context at statement level =================================== ======================================= SPD: BEGIN context at query block level ======================================= Query Block SEL$1 (#0) Return code in qosdSetupDirCtx4QB: NOCTX ===================================== SPD: END context at query block level ===================================== SPD: Return code in qosdDSDirSetup: NOCTX, estType = TABLE SPD: Generating finding id: type = 1, reason = 1, objcnt = 1, obItr = 0, objid = 92197, objtyp = 1, vecsize = 6, colvec = [4, 5, ], fid = 2896834833840853267 SPD: Inserted felem, fid=2896834833840853267, ftype = 1, freason = 1, dtype = 0, dstate = 0, dflag = 0, ver = YES, keep = YES SPD: qosdCreateFindingSingTab retCode = CREATED, fid = 2896834833840853267 SPD: qosdCreateDirCmp retCode = CREATED, fid = 2896834833840853267 SPD: Return code in qosdDSDirSetup: NOCTX, estType = TABLE SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = JOIN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SKIP_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = JOIN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_SCAN SPD: Return code in qosdDSDirSetup: NOCTX, estType = INDEX_FILTER SPD: Generating finding id: type = 1, reason = 1, objcnt = 1, obItr = 0, objid = 92197, objtyp = 1, vecsize = 6, colvec = [4, 5, ], fid = 2896834833840853267 SPD: Modified felem, fid=2896834833840853267, ftype = 1, freason = 1, dtype = 0, dstate = 0, dflag = 0, ver = YES, keep = YES SPD: Generating finding id: type = 1, reason = 1, objcnt = 1, obItr = 0, objid = 92194, objtyp = 1, vecsize = 2, colvec = [1, ], fid = 5618517328604016300 SPD: Modified felem, fid=5618517328604016300, ftype = 1, freason = 1, dtype = 0, dstate = 0, dflag = 0, ver = NO, keep = NO SPD: Generating finding id: type = 1, reason = 1, objcnt = 1, obItr = 0, objid = 92194, objtyp = 1, vecsize = 2, colvec = [1, ], fid = 1142802697078608149 SPD: Modified felem, fid=1142802697078608149, ftype = 1, freason = 1, dtype = 0, dstate = 0, dflag = 0, ver = NO, keep = NO SPD: Generating finding id: type = 1, reason = 2, objcnt = 2, obItr = 0, objid = 92194, objtyp = 1, vecsize = 0, obItr = 1, objid = 92197, objtyp = 1, vecsize = 0, fid = 1437680122701058051 SPD: Modified felem, fid=1437680122701058051, ftype = 1, freason = 2, dtype = 0, dstate = 0, dflag = 0, ver = NO, keep = NO select * from table(dbms_xplan.display_cursor(format=>'report')) ; ????report????adaptive plan Adaptive plan: ------------- This cursor has an adaptive plan, but adaptive plans are enabled for reporting mode only.  The plan that would be executed if adaptive plans were enabled is displayed below. ------------------------------------------------------------------------------------------ | Id  | Operation          | Name                | Rows  | Bytes | Cost (%CPU)| Time     | ------------------------------------------------------------------------------------------ |   0 | SELECT STATEMENT   |                     |       |       |     7 (100)|          | |*  1 |  HASH JOIN         |                     |     4 |   128 |     7   (0)| 00:00:01 | |*  2 |   TABLE ACCESS FULL| ORDER_ITEMS         |     4 |    48 |     3   (0)| 00:00:01 | |   3 |   TABLE ACCESS FULL| PRODUCT_INFORMATION |     1 |    20 |     1   (0)| 00:00:01 | ------------------------------------------------------------------------------------------ SQL> select SQL_ID,IS_RESOLVED_DYNAMIC_PLAN,sql_text from v$SQL WHERE SQL_TEXT like '%MALCEAN%' and sql_text not like '%like%'; SQL_ID IS -------------------------- -- SQL_TEXT -------------------------------------------------------------------------------- 6ydj1bn1bng17 Y select /*MALCEAN*/ product_name from oe.order_items o, oe.product_information p where o.unit_price=15 and quantity>1 and p.product_id=o.product_id ???? explain plan for ????default plan, ??????optimizer???final plan,??V$SQL.IS_RESOLVED_DYNAMIC_PLAN???Y,????????????? DBA_SQL_PLAN_DIRECTIVES?????????????SQL PLAN DIRECTIVES, ???12c? ???MMON?????DML ???column usage??????????,????SMON??? MMON????SGA??PLAN DIRECTIVES??? ?????DBMS_SPD.flush_sql_plan_directive???? select directive_id,type,reason from DBA_SQL_PLAN_DIRECTIVES / DIRECTIVE_ID TYPE REASON ----------------------------------- -------------------------------- ----------------------------- 10321283028317893030 DYNAMIC_SAMPLING JOIN CARDINALITY MISESTIMATE 4757086536465754886 DYNAMIC_SAMPLING JOIN CARDINALITY MISESTIMATE 16085268038103121260 DYNAMIC_SAMPLING JOIN CARDINALITY MISESTIMATE SQL> set pages 9999 SQL> set lines 300 SQL> col state format a5 SQL> col subobject_name format a11 SQL> col col_name format a11 SQL> col object_name format a13 SQL> select d.directive_id, o.object_type, o.object_name, o.subobject_name col_name, d.type, d.state, d.reason 2 from dba_sql_plan_directives d, dba_sql_plan_dir_objects o 3 where d.DIRECTIVE_ID=o.DIRECTIVE_ID 4 and o.object_name in ('ORDER_ITEMS') 5 order by d.directive_id; DIRECTIVE_ID OBJECT_TYPE OBJECT_NAME COL_NAME TYPE STATE REASON ------------ ------------ ------------- ----------- -------------------------------- ----- ------------------------------------- --- 1.8156E+19 COLUMN ORDER_ITEMS UNIT_PRICE DYNAMIC_SAMPLING NEW SINGLE TABLE CARDINALITY MISESTIMATE 1.8156E+19 TABLE ORDER_ITEMS DYNAMIC_SAMPLING NEW SINGLE TABLE CARDINALITY MISESTIMATE 1.8156E+19 COLUMN ORDER_ITEMS QUANTITY DYNAMIC_SAMPLING NEW SINGLE TABLE CARDINALITY MISESTIMATE DBA_SQL_PLAN_DIRECTIVES????? _BASE_OPT_DIRECTIVE ? _BASE_OPT_FINDING SELECT d.dir_own#, d.dir_id, d.f_id, decode(type, 1, 'DYNAMIC_SAMPLING', 'UNKNOWN'), decode(state, 1, 'NEW', 2, 'MISSING_STATS', 3, 'HAS_STATS', 4, 'CANDIDATE', 5, 'PERMANENT', 6, 'DISABLED', 'UNKNOWN'), decode(bitand(flags, 1), 1, 'YES', 'NO'), cast(d.created as timestamp), cast(d.last_modified as timestamp), -- Please see QOSD_DAYS_TO_UPDATE and QOSD_PLUS_SECONDS for more details -- about 6.5 cast(d.last_used as timestamp) - NUMTODSINTERVAL(6.5, 'day') FROM sys.opt_directive$ d ??dbms_spd??? SQL PLAN DIRECTIVES, SQL PLAN DIRECTIVES???retention ???53?: Package: DBMS_SPD This package provides subprograms for managing Sql Plan Directives(SPD). SPD are objects generated automatically by Oracle server. For example, if server detects that the single table cardinality estimated by optimizer is off from the actual number of rows returned when accessing the table, it will automatically create a directive to do dynamic sampling for the table. When any Sql statement referencing the table is compiled, optimizer will perform dynamic sampling for the table to get more accurate estimate. Notes: DBMSL_SPD is a invoker-rights package. The invoker requires ADMINISTER SQL MANAGEMENT OBJECT privilege for executing most of the subprograms of this package. Also the subprograms commit the current transaction (if any), perform the operation and commit it again. DBA view dba_sql_plan_directives shows all the directives created in the system and the view dba_sql_plan_dir_objects displays the objects that are included in the directives. -- Default value for SPD_RETENTION_WEEKS SPD_RETENTION_WEEKS_DEFAULT CONSTANT varchar2(4) := '53'; | STATE : NEW : Newly created directive. | : MISSING_STATS : The directive objects do not | have relevant stats. | : HAS_STATS : The objects have stats. | : PERMANENT : A permanent directive. Server | evaluated effectiveness and these | directives are useful. | | AUTO_DROP : YES : Directive will be dropped | automatically if not | used for SPD_RETENTION_WEEKS. | This is the default behavior. | NO : Directive will not be dropped | automatically. Procedure: flush_sql_plan_directive This procedure allows manually flushing the Sql Plan directives that are automatically recorded in SGA memory while executing sql statements. The information recorded in SGA are periodically flushed by oracle background processes. This procedure just provides a way to flush the information manually. ????”_optimizer_dynamic_plans”(enable dynamic plans)????????,???TRUE??DYNAMIC PLAN? ???FALSE???????????? ????,Dynamic Plan????????????Nested Loop?Hash Join???case ,????????Nested loop???????????HASH JOIN,?HASH JOIN????????????????? ????????subplan?????,???? pass?? ?join method???,?????STATISTICS COLLECTOR???cardinality?,???????HASH JOIN?????Nested Loop,????????????subplan?????access path; ???????Sales??????????????????,????HASH JOIN,??SUBPLAN??customers?????????;?????Nested Loop,???????cust_id?????Range Scan+Access by Rowid? Cardinality feedback Cardinality feedback????????11.2????,????????re-optimization???;  ???????????,Cardinality feedback?????????????????????????? ???????????????????,?????????????????,??????????Cardinality feedback????????????? ????????????????????????? ??????????????Cardinality feedback ??: ????????,???????????,??????????,????????????????selectivity ??? ????????????: ??????,?????????????????????????????????,??????????????????? ????????????????????????????????????????,?????????????????????????? ?????????,???????????????,?????????? ??????????Cardinality ????,??????join Cardinality ????????? Cardinality feedback???????cursor?,?Cursor???aged out????? SELECT /*+ gather_plan_statistics */ product_name FROM order_items o, product_information p WHERE o.unit_price = 15 AND quantity > 1 AND p.product_id = o.product_id Plan hash value: 1553478007 ---------------------------------------------------------------------------------------------------------------------------------------- | Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | Reads | OMem | 1Mem | Used-Mem | ---------------------------------------------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | | 13 |00:00:00.01 | 24 | 20 | | | | |* 1 | HASH JOIN | | 1 | 4 | 13 |00:00:00.01 | 24 | 20 | 2061K| 2061K| 429K (0)| |* 2 | TABLE ACCESS FULL| ORDER_ITEMS | 1 | 4 | 13 |00:00:00.01 | 7 | 6 | | | | | 3 | TABLE ACCESS FULL| PRODUCT_INFORMATION | 1 | 1 | 288 |00:00:00.01 | 17 | 14 | | | | ---------------------------------------------------------------------------------------------------------------------------------------- SELECT /*+ gather_plan_statistics */ product_name FROM order_items o, product_information p WHERE o.unit_price = 15 AND quantity > 1 AND p.product_id = o.product_id Plan hash value: 1553478007 ------------------------------------------------------------------------------------------------------------------------------- | Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem | ------------------------------------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | | 13 |00:00:00.01 | 24 | | | | |* 1 | HASH JOIN | | 1 | 13 | 13 |00:00:00.01 | 24 | 2061K| 2061K| 413K (0)| |* 2 | TABLE ACCESS FULL| ORDER_ITEMS | 1 | 13 | 13 |00:00:00.01 | 7 | | | | | 3 | TABLE ACCESS FULL| PRODUCT_INFORMATION | 1 | 288 | 288 |00:00:00.01 | 17 | | | | ------------------------------------------------------------------------------------------------------------------------------- Note ----- - statistics feedback used for this statement SQL> select count(*) from v$SQL where SQL_ID='cz0hg2zkvd10y'; COUNT(*) ---------- 2 SQL>select sql_ID,USE_FEEDBACK_STATS FROM V$SQL_SHARED_CURSOR where USE_FEEDBACK_STATS ='Y'; SQL_ID U ------------- - cz0hg2zkvd10y Y ????????Cardinality feedback????,???????????????????????????,????????????order_items???????? ????2??????plan hash value??(??????????),?????2????child cursor??????gather_plan_statistics???actual : A-ROWS  estimate :E-ROWS????????? Automatic Re-optimization ???dynamic plan, Re-optimization???????????????  ?  ??????????????? ????????????????????????????????  ???????????,??????????????, ???????????????????? ???????????  Re-optimization??, ????????????????????? Re-optimization????dynamic plan??????????  dynamic plan????????????????????, ???????????????????? ????,??????????join order ??????????????,?????????????join order????? ??????,????????Re-optimization, ??Re-optimization ??????????????????? ?Oracle database 12c?,join statistics?????????????????????,??????????????????????Re-optimization???????????adaptive cursor sharing????? ????????????????,???????????? ????? ???????statistics collectors ????????????????????Re-optimization??????2?????????????,???????????????? ??????????????Re-optimization?????,?????????????????????? ???v$SQL??????IS_REOPTIMIZABLE?????????????????????Re-optimization,??????????Re-optimization???,?????Re-optimization ,???????reporting????? IS_REOPTIMIZABLE VARCHAR2(1) This columns shows whether the next execution matching this child cursor will trigger a reoptimization. The values are:   Y: If the next execution will trigger a reoptimization R: If the child cursor contains reoptimization information, but will not trigger reoptimization because the cursor was compiled in reporting mode N: If the child cursor has no reoptimization information ??1: select plan_table_output from table (dbms_xplan.display_cursor('gwf99gfnm0t7g',NULL,'ALLSTATS LAST')); SQL_ID  gwf99gfnm0t7g, child number 0 ------------------------------------- SELECT /*+ SFTEST gather_plan_statistics */ o.order_id, v.product_name FROM  orders o,   ( SELECT order_id, product_name FROM order_items o, product_information p     WHERE  p.product_id = o.product_id AND list_price < 50 AND min_price < 40  ) v WHERE o.order_id = v.order_id Plan hash value: 1906736282 ------------------------------------------------------------------------------------------------------------------------------------------- | Id  | Operation             | Name                | Starts | E-Rows | A-Rows |   A-Time   | Buffers | Reads  |  OMem |  1Mem | Used-Mem | ------------------------------------------------------------------------------------------------------------------------------------------- |   0 | SELECT STATEMENT      |                     |      1 |        |    269 |00:00:00.02 |    1336 |     18 |       |       |          | |   1 |  NESTED LOOPS         |                     |      1 |      1 |    269 |00:00:00.02 |    1336 |     18 |       |       |          | |   2 |   MERGE JOIN CARTESIAN|                     |      1 |      4 |   9135 |00:00:00.02 |      34 |     15 |       |       |          | |*  3 |    TABLE ACCESS FULL  | PRODUCT_INFORMATION |      1 |      1 |     87 |00:00:00.01 |      33 |     14 |       |       |          | |   4 |    BUFFER SORT        |                     |     87 |    105 |   9135 |00:00:00.01 |       1 |      1 |  4096 |  4096 | 4096  (0)| |   5 |     INDEX FULL SCAN   | ORDER_PK            |      1 |    105 |    105 |00:00:00.01 |       1 |      1 |       |       |          | |*  6 |   INDEX UNIQUE SCAN   | ORDER_ITEMS_UK      |   9135 |      1 |    269 |00:00:00.01 |    1302 |      3 |       |       |          | ------------------------------------------------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): ---------------------------------------------------    3 - filter(("MIN_PRICE"<40 AND "LIST_PRICE"<50))    6 - access("O"."ORDER_ID"="ORDER_ID" AND "P"."PRODUCT_ID"="O"."PRODUCT_ID") SQL_ID  gwf99gfnm0t7g, child number 1 ------------------------------------- SELECT /*+ SFTEST gather_plan_statistics */ o.order_id, v.product_name FROM  orders o,   ( SELECT order_id, product_name FROM order_items o, product_information p     WHERE  p.product_id = o.product_id AND list_price < 50 AND min_price < 40  ) v WHERE o.order_id = v.order_id Plan hash value: 35479787 -------------------------------------------------------------------------------------------------------------------------------------------- | Id  | Operation              | Name                | Starts | E-Rows | A-Rows |   A-Time   | Buffers | Reads  |  OMem |  1Mem | Used-Mem | -------------------------------------------------------------------------------------------------------------------------------------------- |   0 | SELECT STATEMENT       |                     |      1 |        |    269 |00:00:00.01 |      63 |      3 |       |       |          | |   1 |  NESTED LOOPS          |                     |      1 |    269 |    269 |00:00:00.01 |      63 |      3 |       |       |          | |*  2 |   HASH JOIN            |                     |      1 |    313 |    269 |00:00:00.01 |      42 |      3 |  1321K|  1321K| 1234K (0)| |*  3 |    TABLE ACCESS FULL   | PRODUCT_INFORMATION |      1 |     87 |     87 |00:00:00.01 |      16 |      0 |       |       |          | |   4 |    INDEX FAST FULL SCAN| ORDER_ITEMS_UK      |      1 |    665 |    665 |00:00:00.01 |      26 |      3 |       |       |          | |*  5 |   INDEX UNIQUE SCAN    | ORDER_PK            |    269 |      1 |    269 |00:00:00.01 |      21 |      0 |       |       |          | -------------------------------------------------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): ---------------------------------------------------    2 - access("P"."PRODUCT_ID"="O"."PRODUCT_ID")    3 - filter(("MIN_PRICE"<40 AND "LIST_PRICE"<50))    5 - access("O"."ORDER_ID"="ORDER_ID") Note -----    - statistics feedback used for this statement    SQL> select IS_REOPTIMIZABLE,child_number FROM V$SQL  A where A.SQL_ID='gwf99gfnm0t7g'; IS CHILD_NUMBER -- ------------ Y             0 N             1    1* select child_number,other_xml From v$SQL_PLAN  where SQL_ID='gwf99gfnm0t7g' and other_xml is not nul SQL> / CHILD_NUMBER OTHER_XML ------------ --------------------------------------------------------------------------------            1 <other_xml><info type="cardinality_feedback">yes</info><info type="db_version">1              2.1.0.1</info><info type="parse_schema"><![CDATA["OE"]]></info><info type="plan_              hash">35479787</info><info type="plan_hash_2">3382491761</info><outline_data><hi              nt><![CDATA[IGNORE_OPTIM_EMBEDDED_HINTS]]></hint><hint><![CDATA[OPTIMIZER_FEATUR              ES_ENABLE('12.1.0.1')]]></hint><hint><![CDATA[DB_VERSION('12.1.0.1')]]></hint><h              int><![CDATA[ALL_ROWS]]></hint><hint><![CDATA[OUTLINE_LEAF(@"SEL$F5BB74E1")]]></              hint><hint><![CDATA[MERGE(@"SEL$2")]]></hint><hint><![CDATA[OUTLINE(@"SEL$1")]]>              </hint><hint><![CDATA[OUTLINE(@"SEL$2")]]></hint><hint><![CDATA[FULL(@"SEL$F5BB7              4E1" "P"@"SEL$2")]]></hint><hint><![CDATA[INDEX_FFS(@"SEL$F5BB74E1" "O"@"SEL$2"              ("ORDER_ITEMS"."ORDER_ID" "ORDER_ITEMS"."PRODUCT_ID"))]]></hint><hint><![CDATA[I              NDEX(@"SEL$F5BB74E1" "O"@"SEL$1" ("ORDERS"."ORDER_ID"))]]></hint><hint><![CDATA[              LEADING(@"SEL$F5BB74E1" "P"@"SEL$2" "O"@"SEL$2" "O"@"SEL$1")]]></hint><hint><![C              DATA[USE_HASH(@"SEL$F5BB74E1" "O"@"SEL$2")]]></hint><hint><![CDATA[USE_NL(@"SEL$              F5BB74E1" "O"@"SEL$1")]]></hint></outline_data></other_xml>            0 <other_xml><info type="db_version">12.1.0.1</info><info type="parse_schema"><![C              DATA["OE"]]></info><info type="plan_hash">1906736282</info><info type="plan_hash              _2">2579473118</info><outline_data><hint><![CDATA[IGNORE_OPTIM_EMBEDDED_HINTS]]>              </hint><hint><![CDATA[OPTIMIZER_FEATURES_ENABLE('12.1.0.1')]]></hint><hint><![CD              ATA[DB_VERSION('12.1.0.1')]]></hint><hint><![CDATA[ALL_ROWS]]></hint><hint><![CD              ATA[OUTLINE_LEAF(@"SEL$F5BB74E1")]]></hint><hint><![CDATA[MERGE(@"SEL$2")]]></hi              nt><hint><![CDATA[OUTLINE(@"SEL$1")]]></hint><hint><![CDATA[OUTLINE(@"SEL$2")]]>              </hint><hint><![CDATA[FULL(@"SEL$F5BB74E1" "P"@"SEL$2")]]></hint><hint><![CDATA[              INDEX(@"SEL$F5BB74E1" "O"@"SEL$1" ("ORDERS"."ORDER_ID"))]]></hint><hint><![CDATA              [INDEX(@"SEL$F5BB74E1" "O"@"SEL$2" ("ORDER_ITEMS"."ORDER_ID" "ORDER_ITEMS"."PROD              UCT_ID"))]]></hint><hint><![CDATA[LEADING(@"SEL$F5BB74E1" "P"@"SEL$2" "O"@"SEL$1              " "O"@"SEL$2")]]></hint><hint><![CDATA[USE_MERGE_CARTESIAN(@"SEL$F5BB74E1" "O"@"              SEL$1")]]></hint><hint><![CDATA[USE_NL(@"SEL$F5BB74E1" "O"@"SEL$2")]]></hint></o              utline_data></other_xml> ??2: SELECT /*+gather_plan_statistics*/ * FROM customers WHERE cust_state_province='CA' AND country_id='US'; SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(FORMAT=>'ALLSTATS LAST')); PLAN_TABLE_OUTPUT ------------------------------------- SQL_ID b74nw722wjvy3, child number 0 ------------------------------------- select /*+gather_plan_statistics*/ * from customers where CUST_STATE_PROVINCE='CA' and country_id='US' Plan hash value: 1683234692 -------------------------------------------------------------------------------------------------- | Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | Reads | -------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | | 29 |00:00:00.01 | 17 | 14 | |* 1 | TABLE ACCESS FULL| CUSTOMERS | 1 | 8 | 29 |00:00:00.01 | 17 | 14 | -------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter(("CUST_STATE_PROVINCE"='CA' AND "COUNTRY_ID"='US')) SELECT SQL_ID, CHILD_NUMBER, SQL_TEXT, IS_REOPTIMIZABLE FROM V$SQL WHERE SQL_TEXT LIKE 'SELECT /*+gather_plan_statistics*/%'; SQL_ID CHILD_NUMBER SQL_TEXT I ------------- ------------ ----------- - b74nw722wjvy3 0 select /*+g Y ather_plan_ statistics* / * from cu stomers whe re CUST_STA TE_PROVINCE ='CA' and c ountry_id=' US' EXEC DBMS_SPD.FLUSH_SQL_PLAN_DIRECTIVE; SELECT TO_CHAR(d.DIRECTIVE_ID) dir_id, o.OWNER, o.OBJECT_NAME, o.SUBOBJECT_NAME col_name, o.OBJECT_TYPE, d.TYPE, d.STATE, d.REASON FROM DBA_SQL_PLAN_DIRECTIVES d, DBA_SQL_PLAN_DIR_OBJECTS o WHERE d.DIRECTIVE_ID=o.DIRECTIVE_ID AND o.OWNER IN ('SH') ORDER BY 1,2,3,4,5; DIR_ID OWNER OBJECT_NAME COL_NAME OBJECT TYPE STATE REASON ----------------------- ----- ------------- ----------- ------ ---------------- ----- ------------------------ 1484026771529551585 SH CUSTOMERS COUNTRY_ID COLUMN DYNAMIC_SAMPLING NEW SINGLE TABLE CARDINALITY MISESTIMATE 1484026771529551585 SH CUSTOMERS CUST_STATE_ COLUMN DYNAMIC_SAMPLING NEW SINGLE TABLE CARDINALITY PROVINCE MISESTIMATE 1484026771529551585 SH CUSTOMERS TABLE DYNAMIC_SAMPLING NEW SINGLE TABLE CARDINALITY MISESTIMATE SELECT /*+gather_plan_statistics*/ * FROM customers WHERE cust_state_province='CA' AND country_id='US'; ELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(FORMAT=>'ALLSTATS LAST')); PLAN_TABLE_OUTPUT ------------------------------------- SQL_ID b74nw722wjvy3, child number 1 ------------------------------------- select /*+gather_plan_statistics*/ * from customers where CUST_STATE_PROVINCE='CA' and country_id='US' Plan hash value: 1683234692 ----------------------------------------------------------------------------------------- | Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | ----------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | | 29 |00:00:00.01 | 17 | |* 1 | TABLE ACCESS FULL| CUSTOMERS | 1 | 29 | 29 |00:00:00.01 | 17 | ----------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter(("CUST_STATE_PROVINCE"='CA' AND "COUNTRY_ID"='US')) Note ----- - cardinality feedback used for this statement SELECT SQL_ID, CHILD_NUMBER, SQL_TEXT, IS_REOPTIMIZABLE FROM V$SQL WHERE SQL_TEXT LIKE 'SELECT /*+gather_plan_statistics*/%'; SQL_ID CHILD_NUMBER SQL_TEXT I ------------- ------------ ----------- - b74nw722wjvy3 0 select /*+g Y ather_plan_ statistics* / * from cu stomers whe re CUST_STA TE_PROVINCE ='CA' and c ountry_id=' US' b74nw722wjvy3 1 select /*+g N ather_plan_ statistics* / * from cu stomers whe re CUST_STA TE_PROVINCE ='CA' and c ountry_id=' US' SELECT /*+gather_plan_statistics*/ CUST_EMAIL FROM CUSTOMERS WHERE CUST_STATE_PROVINCE='MA' AND COUNTRY_ID='US'; SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(FORMAT=>'ALLSTATS LAST')); PLAN_TABLE_OUTPUT ------------------------------------- SQL_ID 3tk6hj3nkcs2u, child number 0 ------------------------------------- Select /*+gather_plan_statistics*/ cust_email From customers Where cust_state_province='MA' And country_id='US' Plan hash value: 1683234692 ------------------------------------------------------------------------------- |Id | Operation | Name | Starts|E-Rows|A-Rows| A-Time |Buffers| ------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | | 2 |00:00:00.01| 16 | |*1 | TABLE ACCESS FULL| CUSTOMERS | 1 | 2| 2 |00:00:00.01| 16 | ----------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter(("CUST_STATE_PROVINCE"='MA' AND "COUNTRY_ID"='US')) Note ----- - dynamic sampling used for this statement (level=2) - 1 Sql Plan Directive used for this statement EXEC DBMS_SPD.FLUSH_SQL_PLAN_DIRECTIVE; SELECT TO_CHAR(d.DIRECTIVE_ID) dir_id, o.OWNER, o.OBJECT_NAME, o.SUBOBJECT_NAME col_name, o.OBJECT_TYPE, d.TYPE, d.STATE, d.REASON FROM DBA_SQL_PLAN_DIRECTIVES d, DBA_SQL_PLAN_DIR_OBJECTS o WHERE d.DIRECTIVE_ID=o.DIRECTIVE_ID AND o.OWNER IN ('SH') ORDER BY 1,2,3,4,5; DIR_ID OW OBJECT_NA COL_NAME OBJECT TYPE STATE REASON ------------------- -- --------- ---------- ------- --------------- ------------- ------------------------ 1484026771529551585 SH CUSTOMERS COUNTRY_ID COLUMN DYNAMIC_SAMPLING MISSING_STATS SINGLE TABLE CARDINALITY MISESTIMATE 1484026771529551585 SH CUSTOMERS CUST_STATE_ COLUMN DYNAMIC_SAMPLING MISSING_STATS SINGLE TABLE CARDINALITY PROVINCE MISESTIMATE 1484026771529551585 SH CUSTOMERS TABLE DYNAMIC_SAMPLING MISSING_STATS SINGLE TABLE CARDINALITY MISESTIMATE

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• x.gif in Apache logs

  - by T. Stone

  I manage a Django site where we host the media on a subdomain. There shouldn't be any requests for media to the main domain. However I keep seeing these requests for "x.gif" showing up in the access logs on the domain that's handled by WSGI (not the media domain). Can anyone explain what this is? X.X.X.X - - [08/Mar/2010:10:04:00 -1000] "GET / HTTP/1.1" 200 3724 X.X.X.X - - [08/Mar/2010:10:04:10 -1000] "GET /x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:04:10 -1000] "GET /x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:04:10 -1000] "GET /x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:04:10 -1000] "GET /x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:04:51 -1000] "GET /x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:04:52 -1000] "GET /x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:04:52 -1000] "GET /x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:04:52 -1000] "GET /x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:04:56 -1000] "GET /contact/ HTTP/1.1" 200 7196 X.X.X.X - - [08/Mar/2010:10:04:58 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:04:58 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:00 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:00 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:00 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:00 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:01 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:01 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:01 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:01 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:02 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:02 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:02 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:02 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:03 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:03 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:03 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:04 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:04 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:04 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:04 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:05 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:05 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:05 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:05 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:06 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:06 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:06 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653 X.X.X.X - - [08/Mar/2010:10:05:06 -1000] "GET /contact/x.gif HTTP/1.1" 404 2653

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• Windows Server 2003 Terminal Server does not give out all available licenses

  - by Erwin Blonk

  I installed the Terminal Server role in Windows Server 2003 Standard 64-bits. Still, only 2 connections are allowed. The License Manager says that there are 10 Device CALs available, which is correct, and that none are given out. For good measure I let the server reboot, to no effect. Before this, there was another server (same Windows, except that it is 32 bits) active as a licensing server. I removed the role first and then then added it to the new server. I then removed the Terminal Server Licensing Server component off the old one and added it to the new one. After that, I added to licenses. When that didn't give the required result, I rebooted to new server. Still, the new server, with licenses and all, acts as if it has the 2 license RDP. The server are all stand-alone, there is no active directory been set up. Both servers are in different workgroups. Update (4/12/10): The server has changed the entries in the Terminal Server Licensing a few times. After installing the licenses it added an entry of which the exact phrasing I forgot but it was about temporary Windows 2003 device licenses. Later it added Windows Server 2003 - TS Per Device CAL. The temporary held 2 licenses (standard RDP licenses, I think) and the other 10. At some point, seemingly unrelated from the testing we did, it used a licenses from the new pool. This morning, 2 licenses were used from the pool of 10 and only 1 from the temporary/RDP pool (I wish I had screenshots to show, it changed every few hours oir so it seems). Although I had already activated the server over the internet, and re-activated it, I decided to go through the whole procedure by phone. Long story short, here is what it says now: Existing Windows 2000 Server, type:built-in [no licenses used, I add for for sake of being complete] Windows Server 2003 - Terminal Server Per Device CAL Token, type:open [none of 10 used] Windows Server 2003 - TS Per Device CAL, type:open [3 of 10 used] As I tried to explain, this is the end result after a few changes, most of which I can't directly connect to any action from my part. Only going to the activation procedure by phone seemed to directly effect the TS, resulting in the above configuration. Still, it is impossible to connect with more than 3 people, which is 1 up from the 2 that could connect yesterday. TS does say 7 licenses are avaible. Yet it won't give them out.

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• Win7 playback of dvr-ms files stutters

  - by Jim Lynn

  I've just had to install Windows 7 on my Media Center machine because my Vista installation had a faulty drive. I've got the latest drivers that I can find - Intel 945GM integrated Graphics, Realtek audio drivers. Things are working OK with one exception. Playback of old recordings, from dvr-ms format files, is choppy. The picture freezes for a fraction of a second, then quickly catches up. The sound is uninterrupted and doesn't pause. These freezes happen once every 5 seconds or so. It's very regular. Playback of Live TV from the digital tuner is perfectly smooth. DVD playback is perfectly smooth. As an experiment, I used the MPEG editing package VideoReDo to create a small test file in three different formats. This program takes the raw MPEG streams and repackages them into the desired container. I took the same clip and created three files in three formats: dvr-ms (Microsoft's old recorded TV format); mpg (standard MPEG); and ts (raw MPEG transport stream of the kind often produced by PVRs). When these three files are played back under Windows 7, the mpg and ts files play smoothly, but the dvr-ms file stutters. The last piece of data I have is that two other Windows 7 machines can play back dvr-ms files smoothly with no stuttering. One is a netbook, with less grunt than the media centre. So there must be something specific about my Media Center machine that's causing the problem. Does anyone have any idea where I can look now? I don't know much about AV software, codecs, filter graphs etc. but I suspect that's where the problem lies. Rendering the video isn't the problem, but extracting the streams is. How would I go about diagnosing the problem? Edited to add: I just used the GraphStudio tool to look at the filter graph on the offending PC. The filter graph it uses by default for dvr-ms looks identical to the other machines, and, interestingly, when I play the files using GraphStudio they run smoothly. Under Windows Media Player and Windows Media Center they stutter. I'd like to see the filter graph for WMP but GraphStudio won't show it. It looks like WMP and WMC are using a different decoding path to GraphStudio. Edited again to add: Today I purchased a new HDTV. The same Media Center driving the TV at 1080p is now playing back the old Recorded TV files smoothly, without stuttering. So whatever the cause of the original problem, using a different resolution seems to have removed the problem. It might also explain why nobody else has had this problem. I doubt many people use Media Centre with a 14in portable TV.

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• Setting up a transparent SSL proxy

  - by badunk

  I've got a linux box set up with 2 network cards to inspect traffic going through port 80. One card is used to go out to the internet, the other one is hooked up to a networking switch. The point is to be able to inspect all HTTP and HTTPS traffic on devices hooked up to that switch for debugging purposes. I've written the following rules for iptables: nat -A PREROUTING -i eth1 -p tcp -m tcp --dport 80 -j DNAT --to-destination 192.168.2.1:1337 -A PREROUTING -i eth1 -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 1337 -A POSTROUTING -s 192.168.2.0/24 -o eth0 -j MASQUERADE On 192.168.2.1:1337, I've got a transparent http proxy using Charles (http://www.charlesproxy.com/) for recording. Everything's fine for port 80, but when I add similar rules for port 443 (SSL) pointing to port 1337, I get an error about invalid message through Charles. I've used SSL proxying on the same computer before with Charles (http://www.charlesproxy.com/documentation/proxying/ssl-proxying/), but have been unsuccessful with doing it transparently for some reason. Some resources I've googled say its not possible - I'm willing to accept that as an answer if someone can explain why. As a note, I have full access to the described set up including all the clients hooked up to the subnet - so I can accept self-signed certs by Charles. The solution doesn't have to be Charles-specific since in theory, any transparent proxy will do. Thanks! Edit: After playing with it a little, I was able to get it working for a specific host. When I modify my iptables to the following (and open 1338 in charles for reverse proxy): nat -A PREROUTING -i eth1 -p tcp -m tcp --dport 80 -j DNAT --to-destination 192.168.2.1:1337 -A PREROUTING -i eth1 -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 1337 -A PREROUTING -i eth1 -p tcp -m tcp --dport 443 -j DNAT --to-destination 192.168.2.1:1338 -A PREROUTING -i eth1 -p tcp -m tcp --dport 443 -j REDIRECT --to-ports 1338 -A POSTROUTING -s 192.168.2.0/24 -o eth0 -j MASQUERADE I am able to get a response, but with no destination host. In the reverse proxy, if I just specify that everything from 1338 goes to a specific host that I wanted to hit, it performs the hand shake properly and I can turn on SSL proxying to inspect the communication. The setup is less than ideal because I don't want to assume everything from 1338 goes to that host - any idea why the destination host is being stripped? Thanks again

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• How to connect SAN from CentOS through two iSCSI Targets

  - by garconcn

  I had asked the similar question before. This time I want to use subnet for two iSCSI Targets, hence I start a new question. I have an old Promise VTrak M500i SAN Server. It comes with 2 iSCSI ports. I want to connect to two LUNs on the SAN server through two separate Targets from CentOS 5.7 64bits server. My network setup is as follows: CentOS server: Management network - 192.168.1.1 Storage network 1 - 192.168.5.2 Storage network 2 - 192.168.6.2 Promise SAN server: Management network - 192.168.1.2 iSCSI Port 1 - 192.168.5.1 iSCSI Port 2 - 192.168.6.1 I have two Logical Drives on this SAN and they are mapped as follows: Index Initiator Name LUN Mapping 0 iqn.2011-11:backup (LD0,0) 1 iqn.2011-11:template (LD1,1) Basically, I want the traffic to iqn.2011-11:backup LUN 0 through 192.168.5.1 network the traffic to iqn.2011-11:template LUN 1 through 192.168.6.1 network I don't use MPIO, just want to separate the traffic to avoid traffic jam. How do I achieve this? I am new to SAN stuff, please explain as much detail as you can. Thank you. The following are what I am doing now. After mapping the LUN to my pre-defined Initiators, the CentOS server can discover both Targets. [root@centos ~]# iscsiadm -m discovery -t sendtargets -p 192.168.5.1 192.168.5.1:3260,1 iscsi-1 192.168.6.1:3260,2 iscsi-1 [root@centos ~]# iscsiadm -m discovery -t sendtargets -p 192.168.6.1 192.168.6.1:3260,2 iscsi-1 192.168.5.1:3260,1 iscsi-1 [root@centos ~]# /etc/init.d/iscsi start iscsid is stopped Starting iSCSI daemon: [ OK ] [ OK ] Setting up iSCSI targets: Logging in to [iface: default, target: iscsi-1, portal: 192.168.6.1,3260] Logging in to [iface: default, target: iscsi-1, portal: 192.168.5.1,3260] Login to [iface: default, target: iscsi-1, portal: 192.168.6.1,3260] successful. Login to [iface: default, target: iscsi-1, portal: 192.168.5.1,3260] successful. [ OK ] [root@centos ~]# iscsiadm -m session tcp: [1] 192.168.6.1:3260,2 iscsi-1 tcp: [2] 192.168.5.1:3260,1 iscsi-1 When I check the LUN mapping on the SAN server for the two Logical Drives, both LUNs are connected through Port0-192.168.5.2 with the Initiator defined in CentOS. Assigned Initiator List: Initiator Name Alias IP Address LUN iqn.2011-11.centos centos.mydomain.com Port0-192.168.5.2 0 Initiator Name Alias IP Address LUN iqn.2011-11.centos centos.mydomain.com Port1-192.168.5.2 1 I assume the following is what I want: Initiator Name Alias IP Address LUN iqn.2011-11.backup centos.mydomain.com Port0-192.168.5.2 0 Initiator Name Alias IP Address LUN iqn.2011-11.template centos.mydomain.com Port0-192.168.6.2 1

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• Real server, Multiple IP Addresses, HyperV Virtual Server, How to partition IPs across real and Virtual NICs

  - by Steven_W

  This is a slightly difficult problem to explain without same basic background information - I'll try and refine the question later as necessary Originally, I have a single hosted server (Win 2008R2) with the following range of 8 IP addresses. - Single NIC - IP: x.x.128.72 -> x.x.128.79 - Subnet: x.x.255.192 - GW: x.x.128.65 After installing Hyper-V and setting up a single virtual server on the same box, I then wanted to assign one of the IP addresses to the virtual server, leaving everything else running normally. -- Firstly, I tried using the "External" network, but (even after setting IPs on the "Virtual Adapter" similar to Here but struggled to get networking running at all. I needed to keep the server running (otherwise I would have spent more time pursuing this approach) Q1 ... Was this a sensible thing to do ? Should I have carried on down this route ? -- I then decided to try different approach - Set the HyperV network to "Internal" (visible to Management OS) - Physical NIC - IP: x.x.128.72 -> x.x.128.75 - Subnet: x.x.255.192 - GW: x.x.128.65 - Virtual NIC - IP: x.x.128.78 - Subnet: x.x.255.252 - GW: x.x.128.72 ... { The same as the IP of the physical NIC ) - Virtual OS-NIC - IP: x.x.128.77 - Subnet: x.x.255.252 - GW: x.x.128.78 ... { The same as the IP of the host virtual-NIC ) -- Surprisingly enough, this approach actually worked, and I was able to connect from all the following: - Internet to/from physical NIC (x.x.128.72) - physical NIC (x.x.128.72) to virtual-OS-NIC (x.x.128.77) e.g. testing via ping + FTP - Internet to/from virtual-OS-NIC (x.x.128.72) -- The problem I have is that this approach seems to only last for a short while (a few hours). After this time, it seems that I lose the ability to connect from Virtual-OS-NIC to/from the internet (but I can still connect from the host-OS to the virtual-OS and from the host-OS to the internet) I have re-tested this a couple of times with the same results ... I leave the server on for a few hours (e.g. overnight), and when I come back in the morning, the Virtual-OS loses the ability to route to the internet -- I'm not quite sure what to look at next (or whether I'm going about this completely the wrong way ) One "possible relevant item" is that the host-OS is also running RRAS (Routing and Remote Access), but this is only to run a simple VPN -- Q2 - Wheat should I be looking at next ? (Any good references / recommendations of what to try) Would appreciate any thoughts or comments (even if you tell me I'm going about this the wrong way)

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• NTPD seems to delete all network interfaces

  - by Aurelin

  We have a couple of virtual interfaces configured on eth0 on a CentOS, and every now and then, they went down seemingly out of the blue. Now after going through the log files, I found out that apparently ntpd deletes all eth0 interfaces, and that dhclient automatically brings eth0 back up. The virtual interfaces, however, stay down which causes several of our websites to be inaccessible. Can someone explain to me why ntpd deletes interfaces? Can / should that be turned off, or can / should I configure dhclient to bring the virtual interfaces back up automatically, too? EDIT// The log files that I should've posted : Nov 12 13:10:28 raptor dhclient[20048]: DHCPREQUEST on eth0 to 255.255.255.255 port 67 (xid=0x6a825e97) Nov 12 13:10:42 raptor dhclient[20048]: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 8 (xid=0x24554092) Nov 12 13:10:42 raptor dhclient[20048]: DHCPOFFER from 96.126.108.78 Nov 12 13:10:42 raptor dhclient[20048]: DHCPREQUEST on eth0 to 255.255.255.255 port 67 (xid=0x24554092) Nov 12 13:10:42 raptor dhclient[20048]: DHCPACK from 96.126.108.78 (xid=0x24554092) Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #31 eth0, 50.116.50.97#123, interface stats: received=3255, sent=3256, dropped=0, active_time=1559394 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #32 eth0:0, 50.116.53.56#123, interface stats: received=3, sent=0, dropped=0, active_time=1559391 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #33 eth0:1, 66.175.211.192#123, interface stats: received=2, sent=0, dropped=0, active_time=1559389 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #34 eth0:2, 50.116.53.95#123, interface stats: received=3, sent=0, dropped=0, active_time=1559387 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #35 eth0:3, 97.107.132.32#123, interface stats: received=2, sent=0, dropped=0, active_time=1559385 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #36 eth0:4, 50.116.56.201#123, interface stats: received=2, sent=0, dropped=0, active_time=1559383 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #37 eth0:5, 66.175.212.121#123, interface stats: received=2, sent=0, dropped=0, active_time=1559381 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #38 eth0:6, 66.175.215.137#123, interface stats: received=2, sent=0, dropped=0, active_time=1559379 secs Nov 12 13:10:44 raptor NET[1573]: /sbin/dhclient-script : updated /etc/resolv.conf Nov 12 13:10:44 raptor dhclient[20048]: bound to 50.116.50.97 -- renewal in 32692 seconds. Nov 12 13:10:45 raptor ntpd[2109]: Listening on interface #39 eth0, 50.116.50.97#123 Enabled The eth0 config : DEVICE="eth0" ONBOOT="yes" BOOTPROTO="dhcp" IPV6INIT="no" IPADDR=50.116.50.97 NETMASK=255.255.255.0 GATEWAY=50.116.50.1 And the virtual interfaces (I posted the first one only, they look the same for the most part) : # Configuration for eth0:0 DEVICE=eth0:0 BOOTPROTO=none # This line ensures that the interface will be brought up during boot. ONBOOT=yes # eth0:0 IPADDR=50.116.53.56 NETMASK=255.255.255.0

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• Best Practise: DNS and VPN (with private network IPs)

  - by ribx

  I am trying to find the best solution for my DNS problem. We are running several services in our company that you can reach only over VPN. Other services, that are reachable through the internet got the domain ... At the moment all services inside the VPN network go by .local... These have an VPN IP of the private network 192.168.252.0/24. Clients reach from Linux over OSX to Windows. I can think of 4 possibilities to implement a DNS infrastructure: Most common: an internal DNS Server, that is pushed by the VPN. But this has several drawbacks: your DNS responses are limited to the speed of the VPN Connection and your own DNS server. Because of very complex websites, this can increase the time for a page to load quite a lot. Also: we have several VPNs that are not connected to each other and all of them have their own DNS server. Several DNS servers locally. These have to be configured by hand. And you have to use some third party tool like dnsmasq. If you start a DNS request, you ask your locally running DNS server, which decides which server to ask for which domain name. One college of mine uses such a solution with this OSX (I am sorry, I don't remember the name of the application). You use your domain hoster. Most of them have APIs available to manipulate your DNS entries. So you could pull your private network informations to your domain hoster. I am not sure whether they all accept private network IPs. But I guess there will be some problems in the same way as in number 4. The one we currently use, because it's for us the most logical choice: we forward the sub domain *.local.. to our own public DNS Server. This works quite good for some public DNS Servers like Google. But most ISPs do not forward the answers. Or don't do that always. Like my ISP sends me a positive result of the a DNS request of a *.local.. domain only every 10th time I make a nslookup. (Can someone explain this?) Here the real Question: Is there another solution we were not thinking about? Or: What of these methods do you use?

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• Why Does Wireless Gear Degrade Over Time?

  - by bahamat

  I saw this originally posted on slashdot, but their comment format is not conducive to actually getting a correct answer. Having directly experienced this phenomenon myself, I'm now asking here where I think I can actually get an educated answer. Here's the original question verbatim: Lately I have replaced several home wireless routers because the signal strength has been found to be degraded. These devices, when new (2+ years ago) would cover an entire house. Over the years, the strength seems to decrease to a point where it might only cover one or two rooms. Of the three that I have replaced for friends, I have not found a common brand, age, etc. It just seems that after time, the signal strength decreases. I know that routers are cheap and easy to replace but I'm curious what actually causes this. I would have assumed that the components would either work or not work; we would either have a full signal or have no signal. I am not an electrical engineer and I can't find the answer online so I'm reaching out to you. Can someone explain how a transmitter can slowly go bad? Common (incorrect, but repeated) answers from slashdot include: Back then your neighbors didn't have wifi, now they do. They drowning you out. I don't think this is likely because replacing the access point with a new one and using the same frequencies solves the problem. Older devices had low transmit power. Crank that baby. As mentioned by a FreeBSD wireless developer this violates regulations and can physically damage the equipment. It was also mentioned that higher power in one direction is not necessarily reciprocated. This shows higher bars, but not necessarily a better connection. Manufacturers make cheap crap designed to wear out. This one actually may be legitimate although it is overly broad. What specifically causes damage over time? Heat? Excessive power? So can anyone provide an informed answer on this? Is there any way to fix these older access points?

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• libvirt qemu/kvm migration problem

  - by Panda

  I am using kvm and libvirt on my Dell server. Now i am trying to migrate one virtual machine from a physical server to another. However, I failed everytime. In virsh on physicalServer1, I typed: virsh # migrate virtualmachine1 qemu+ssh://username@physicalServer2/system error: operation failed: migration to 'tcp:physicalServer2:49163' failed: migration failed Then I searched FAQ part on libvirt.org. It says: error: operation failed: migration to '...' failed: migration failed This is an error often encountered when trying to migrate with QEMU/KVM. This typically happens with plain migration, when the source VM cannot connect to the destination host. You will want to make sure your hosts are properly configured for migration (see the migration section of this FAQ) I managed to ssh physicalServer2 from a shell on virtualmachine1 so the above red part did not explain my failure. I also open ports on physicalServer2, iptables -L shows following information: Chain INPUT (policy ACCEPT) target prot opt source destination ACCEPT udp -- anywhere anywhere udp dpt:domain ACCEPT tcp -- anywhere anywhere tcp dpt:domain ACCEPT udp -- anywhere anywhere udp dpt:bootps ACCEPT tcp -- anywhere anywhere tcp dpt:bootps ACCEPT udp -- anywhere anywhere udp dpt:domain ACCEPT tcp -- anywhere anywhere tcp dpt:domain ACCEPT udp -- anywhere anywhere udp dpt:bootps ACCEPT tcp -- anywhere anywhere tcp dpt:bootps ACCEPT tcp -- anywhere anywhere state NEW tcp dpts:49152:49215 Chain FORWARD (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere 192.168.122.0/24 state RELATED,ESTABLISHED ACCEPT all -- 192.168.122.0/24 anywhere ACCEPT all -- anywhere anywhere REJECT all -- anywhere anywhere reject-with icmp-port-unreachable REJECT all -- anywhere anywhere reject-with icmp-port-unreachable ACCEPT all -- anywhere 192.168.122.0/24 state RELATED,ESTABLISHED ACCEPT all -- 192.168.122.0/24 anywhere ACCEPT all -- anywhere anywhere REJECT all -- anywhere anywhere reject-with icmp-port-unreachable REJECT all -- anywhere anywhere reject-with icmp-port-unreachable Chain OUTPUT (policy ACCEPT) target prot opt source destination The /var/log/libvirt/qemu/virtualmachine1.log on physicalServer2: 2011-05-06 13:37:30.708: starting up LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/sbin:/sbin:/bin QEMU_AUDIO_DRV=none /usr/bin/kvm -S -M pc-0.14 -enable-kvm -m 2048 -smp 1,sockets=1,cores=1,threads=1 -name openjudge-test -uuid a8c704bc-a4f9-90db-3e57-40e60b00aac1 -nodefconfig -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/virtualmachine1.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=readline -rtc base=utc -boot c -drive file=/media/nfs/virtualmachine1.img,if=none,id=drive-ide0-0-0,format=raw -device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0 -drive if=none,media=cdrom,id=drive-ide0-1-0,readonly=on,format=raw -device ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -netdev tap,fd=20,id=hostnet0 -device rtl8139,netdev=hostnet0,id=net0,mac=00:16:36:8a:22 :a0,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -usb -vnc 127.0.0.1:2 -vga cirrus -incoming tcp:0.0.0.0:49163 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4 char device redirected to /dev/pts/0 2011-05-06 13:37:30.915: shutting down The /var/log/libvirt/qemu/virtualmachine1.log on physicalServer1 is empty. Both physical servers are using Ubuntu 11.04. The libvirt and kvm used are installed by apt-get. The libvirt version is 0.8.8.

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• Forward all traffic through an ssh tunnel

  - by Eamorr

  I hope someone can follow this and I'll explain as best I can. I'm trying to forward all traffic from port 6999 on x.x.x.224, through an ssh tunnel, and onto port 7000 on x.x.x.218. Here is some ASCII art: |browser|-----|Squid on x.x.x.224|------|ssh tunnel|------<satellite link>-----|Squid on x.x.x.218|-----|www| 3128 6999 7000 80 When I remove the ssh tunnel, everything works fine. The idea is to turn off encryption on the ssh tunnel (to save bandwidth) and turn on maximum compression (to save more bandwidth). This is because it's a satellite link. Here's the ssh tunnel I've been using: ssh -C -f -C -o CompressionLevel=9 -o Cipher=none [email protected] -L 7000:172.16.1.224:6999 -N The trouble is, I don't know how to get data from Squid on x.x.x.224 into the ssh tunnel? Am I going about this the wrong way? Should I create an ssh tunnel on x.x.x.218? I use iptables to stop squid on x.x.x.224 from reading port 80, but to feed from port 6999 instead (i.e. via the ssh tunnel). Do I need another iptables rule? Any comments greatly appreciated. Many thanks in advance, Regarding Eduardo Ivanec's question, here is a netstat -i any port 7000 -nn dump from x.x.x.218: 14:42:15.386462 IP 172.16.1.224.40006 > 172.16.1.218.7000: Flags [S], seq 2804513708, win 14600, options [mss 1460,sackOK,TS val 86702647 ecr 0,nop,wscale 4], length 0 14:42:15.386690 IP 172.16.1.218.7000 > 172.16.1.224.40006: Flags [R.], seq 0, ack 2804513709, win 0, length 0 Update 2: When I run the second command, I get the following error in my browser: ERROR The requested URL could not be retrieved The following error was encountered while trying to retrieve the URL: http://109.123.109.205/index.php Zero Sized Reply Squid did not receive any data for this request. Your cache administrator is webmaster. Generated Fri, 01 Jul 2011 16:06:06 GMT by remote-site (squid/2.7.STABLE9) remote-site is 172.16.1.224 When I do a tcpdump -i any port 7000 -nn I get the following: root@remote-site:~# tcpdump -i any port 7000 -nn tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on any, link-type LINUX_SLL (Linux cooked), capture size 65535 bytes channel 2: open failed: connect failed: Connection refused channel 2: open failed: connect failed: Connection refused channel 2: open failed: connect failed: Connection refused channel 2: open failed: connect failed: Connection refused channel 2: open failed: connect failed: Connection refused channel 2: open failed: connect failed: Connection refused channel 2: open failed: connect failed: Connection refused channel 2: open failed: connect failed: Connection refused channel 2: open failed: connect failed: Connection refused channel 2: open failed: connect failed: Connection refused channel 2: open failed: connect failed: Connection refused

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• Ubuntu Natty: 32-bit userland, 64-bit kernel?

  - by dsimcha

  I'm trying to manually install a 64-bit kernel for 32-bit Ubuntu. I have my reasons for doing so, but they're too complicated to explain here. Prior to Natty, this worked fine. Now, on Natty, I get the following error message when I try doing it the same way: dsimcha@dsimcha-laptop:~$ sudo dpkg -i --force-architecture linux-image-2.6.38-8-server_2.6.38-8.42_amd64.deb [sudo] password for dsimcha: dpkg: error processing linux-image-2.6.38-8-server_2.6.38-8.42_amd64.deb (--install): cannot access archive: No such file or directory Errors were encountered while processing: linux-image-2.6.38-8-server_2.6.38-8.42_amd64.deb dsimcha@dsimcha-laptop:~$ cd Downloads/ dsimcha@dsimcha-laptop:~/Downloads$ sudo dpkg -i --force-architecture linux-image-2.6.38-8-server_2.6.38-8.42_amd64.deb dpkg: warning: overriding problem because --force enabled: package architecture (amd64) does not match system (i386) (Reading database ... 159153 files and directories currently installed.) Preparing to replace linux-image-2.6.38-8-server:amd64 2.6.38-8.42 (using linux-image-2.6.38-8-server_2.6.38-8.42_amd64.deb) ... Done. Unpacking replacement linux-image-2.6.38-8-server:amd64 ... Examining /etc/kernel/postrm.d . run-parts: executing /etc/kernel/postrm.d/initramfs-tools 2.6.38-8-server /boot/vmlinuz-2.6.38-8-server run-parts: executing /etc/kernel/postrm.d/zz-update-grub 2.6.38-8-server /boot/vmlinuz-2.6.38-8-server dpkg: dependency problems prevent configuration of linux-image-2.6.38-8-server:amd64: linux-image-2.6.38-8-server:amd64 depends on initramfs-tools (>= 0.36ubuntu6). linux-image-2.6.38-8-server:amd64 depends on coreutils | fileutils (>= 4.0); however: Package coreutils:amd64 is not installed. linux-image-2.6.38-8-server:amd64 depends on module-init-tools (>= 3.3-pre11-4ubuntu3); however: linux-image-2.6.38-8-server:amd64 depends on wireless-crda; however: dpkg: error processing linux-image-2.6.38-8-server:amd64 (--install): dependency problems - leaving unconfigured Errors were encountered while processing: linux-image-2.6.38-8-server:amd64 When I try the dependencies manually, I get, for example: dsimcha@dsimcha-laptop:~/Downloads$ sudo dpkg -i --force-architecture coreutils_8.5-1ubuntu6_amd64.deb dpkg: warning: overriding problem because --force enabled: package architecture (amd64) does not match system (i386) dpkg: error processing coreutils_8.5-1ubuntu6_amd64.deb (--install): coreutils:amd64 8.5-1ubuntu6 (Multi-Arch: no) is not co-installable with coreutils:i386 8.5-1ubuntu6 (Multi-Arch: no) which is currently installed Errors were encountered while processing: coreutils_8.5-1ubuntu6_amd64.deb Has anyone had any success installing 64-bit kernels on 32-bit Natty? If so, how can this be done?

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• Apache Simple Configuration Issue: Setting up per-user directory permission denied problem

  - by Huckphin

  Hello. I am just getting Apache 2.2 running on Fedora 13 Beta 64-bit. I am running into issues setting my per-user directory. The goal is to make localhost/~user map to /home/~user/public_html. I think that I have the permissions right because I have 755 to /home/~user, and I have 755 to /home/~user/public_html/ and I have 777 for all contents inside of /home/~user/public_html/ recursively set. My mod_userdir configuration looks like this: <IfModule mod_userdir.c> # # UserDir is disabled by default since it can confirm the presence # of a username on the system (depending on home directory # permissions). # UserDir disabled root UserDir enabled huckphin # # To enable requests to /~user/ to serve the user's public_html # directory, remove the "UserDir disabled" line above, and uncomment # the following line instead: # UserDir public_html The error that I am seeing in the error log is this: [Sat May 15 09:54:29 2010] [error] [client 127.0.0.1] (13)Permission denied: access to /~huckphin/index.html denied When I login as the apache user, I know that /~huckphin does not exist, and this is not what I want. I want it to be accessing ~huckphin, not /~huckphin. What do I need to change on my configuration for this to work? [Added after comments] Hi Andol, thank you for your suggestions. So, first off, you said that you assume that I have the userdir module enabled, but I am not sure what that means exactly. That could be part of the problem. I do have the Module loaded, using the LoadModule directive. I have this: LoadModule userdir_module modules/mod_userdir.so I also did a find on where mod_userdir is, and I found it located here: [huckphin@crhyner-workbox]/% find / . -name '*mod_userdir.so*' 2> /dev/null /usr/lib64/lighttpd/mod_userdir.so /usr/lib64/httpd/modules/mod_userdir.so Is there something else I need to enable? Also, my directory configuration was mentioned. I have uncommented the default configuration given. I have not looked into what all of the configurations mean, and this could probably explain the issue. Here is the Directory that I have for the user directories: <Directory "/home/*/public_html"> AllowOverride FileInfo AuthConfig Limit Options MultiViews Indexes SymLinksIfOwnerMatch IncludesNoExec <Limit GET POST OPTIONS> Order allow,deny Allow from all </Limit> <LimitExcept GET POST OPTIONS> Order deny,allow Deny from all </LimitExcept> </Directory>

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• Having trouble Getting "RTSP over HTTP"

  - by Muhammad Adeel Zahid

  There is an axis camera that is connected to our site (camba.tv) through axis one click connection component (which acts as proxy). We can communicate with this camera only through http by setting the proxy to our OCCC server's address. If we want to get RTSP streams (h.264) we are only left with "RTSP over HTTP" option. For this I have followed axis VAPIX 3 documentation section 3.3. I issue requests through fiddler but don't get any response. But when i put the URL (axrtsphttp://1.00408CBEA38B/axis-media/media.amp) in windows media player (with proxy set to OCCC server 212.78.237.156:3128) the player is able to get RTSP stream over HTTP after logging in. I have created a request trace of communication between camera and windows media player through wireshark and the request that brings the stream looks like http://1.00408cbea38b/axis-media/media.amp HTTP/1.1 x-sessioncookie: 619 User-Agent: Axis AMC Host: 1.00408CBEA38B Proxy-Connection: Keep-Alive Pragma: no-cache Authorization: Digest username="root",realm="AXIS_00408CBEA38B",nonce="000a8b40Y0100409c13ac7e6cceb069289041d8feb1691",uri="/axis-media/media.amp",cnonce="9946e2582bd590418c9b70e1b17956c7",nc=00000001,response="f3cab86fc84bfe33719675848e7fdc0a",qop="auth" HTTP/1.0 200 OK Content-Type: application/x-rtsp-tunnelled Date: Tue, 02 Nov 2010 11:45:23 GMT RTSP/1.0 200 OK CSeq: 1 Content-Type: application/sdp Content-Base: rtsp://1.00408CBEA38B/axis-media/media.amp/ Date: Tue, 02 Nov 2010 11:45:23 GMT Content-Length: 410 v=0 o=- 1288698323798001 1288698323798001 IN IP4 1.00408CBEA38B s=Media Presentation e=NONE c=IN IP4 0.0.0.0 b=AS:50000 t=0 0 a=control:* a=range:npt=0.000000- m=video 0 RTP/AVP 96 b=AS:50000 a=framerate:30.0 a=transform:1,0,0;0,1,0;0,0,1 a=control:trackID=1 a=rtpmap:96 H264/90000 a=fmtp:96 packetization-mode=1; profile-level-id=420029; sprop-parameter-sets=Z0IAKeNQFAe2AtwEBAaQeJEV,aM48gA== RTSP/1.0 200 OK CSeq: 2 Session: 3F4763D8; timeout=60 Transport: RTP/AVP/TCP;unicast;interleaved=0-1;ssrc=060922C6;mode="PLAY" Date: Tue, 02 Nov 2010 11:45:24 GMT RTSP/1.0 200 OK CSeq: 3 Session: 3F4763D8 Range: npt=0- RTP-Info: url=rtsp://1.00408CBEA38B/axis-media/media.amp/trackID=1;seq=7392;rtptime=4190934902 Date: Tue, 02 Nov 2010 11:45:24 GMT [Binary Stream Content] But when i copy this request to fiddler, I only get 200 status code with content-type set to application/x-rtsp-tunneled and there is no stream data. The only thing i do different with stream is to use Basic in authorization header instead of Digest and I do not get 401 (Un authorized) status code. Can anyone explain what's happening here? How can I write request sequences to get stream in fiddler? If it is needed, I can upload the wireshark request dump somewhere.

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• Windows 7 playback of dvr-Microsoft files stutters

  - by Jim Lynn

  I've just had to install Windows 7 on my Media Center machine because my Vista installation had a faulty drive. I've got the latest drivers that I can find - Intel 945GM integrated Graphics, Realtek audio drivers. Things are working OK with one exception. Playback of old recordings, from dvr-Microsoft format files, is choppy. The picture freezes for a fraction of a second, then quickly catches up. The sound is uninterrupted and doesn't pause. These freezes happen once every 5 seconds or so. It's very regular. Playback of Live TV from the digital tuner is perfectly smooth. DVD playback is perfectly smooth. As an experiment, I used the MPEG editing package VideoReDo to create a small test file in three different formats. This program takes the raw MPEG streams and repackages them into the desired container. I took the same clip and created three files in three formats: dvr-Microsoft (Microsoft's old recorded TV format); mpg (standard MPEG); and ts (raw MPEG transport stream of the kind often produced by PVRs). When these three files are played back under Windows 7, the mpg and ts files play smoothly, but the dvr-Microsoft file stutters. The last piece of data I have is that two other Windows 7 machines can play back dvr-Microsoft files smoothly with no stuttering. One is a netbook, with less grunt than the media centre. So there must be something specific about my Media Center machine that's causing the problem. Does anyone have any idea where I can look now? I don't know much about AV software, codecs, filter graphs etc. but I suspect that's where the problem lies. Rendering the video isn't the problem, but extracting the streams is. How would I go about diagnosing the problem? Edited to add: I just used the GraphStudio tool to look at the filter graph on the offending PC. The filter graph it uses by default for dvr-Microsoft looks identical to the other machines, and, interestingly, when I play the files using GraphStudio they run smoothly. Under Windows Media Player and Windows Media Center they stutter. I'd like to see the filter graph for Windows Media Player but GraphStudio won't show it. It looks like Windows Media Player and WMC are using a different decoding path to GraphStudio. Edited again to add: Today I purchased a new HDTV. The same Media Center driving the TV at 1080p is now playing back the old Recorded TV files smoothly, without stuttering. So whatever the cause of the original problem, using a different resolution seems to have removed the problem. It might also explain why nobody else has had this problem. I doubt many people use Media Centre with a 14in portable TV.

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• How Do I Restrict Repository Access via WebSVN?

  - by kaybenleroll

  I have multiple subversion repositories which are served up through Apache 2.2 and WebDAV. They are all located in a central place, and I used this debian-administration.org article as the basis (I dropped the use of the database authentication for a simple htpasswd file though). Since then, I have also started using WebSVN. My issue is that not all users on the system should be able to access the different repositories, and the default setup of WebSVN is to allow anyone who can authenticate. According to the WebSVN documentation, the best way around this is to use subversion's path access system, so I looked to create this, using the AuthzSVNAccessFile directive. When I do this though, I keep getting "403 Forbidden" messages. My files look like the following: I have default policy settings in a file: <Location /svn/> DAV svn SVNParentPath /var/lib/svn/repository Order deny,allow Deny from all </Location> Each repository gets a policy file like below: <Location /svn/sysadmin/> Include /var/lib/svn/conf/default_auth.conf AuthName "Repository for sysadmin" require user joebloggs jimsmith mickmurphy </Location> The default_auth.conf file contains this: SVNParentPath /var/lib/svn/repository AuthType basic AuthUserFile /var/lib/svn/conf/.dav_svn.passwd AuthzSVNAccessFile /var/lib/svn/conf/svnaccess.conf I am not fully sure why I need the second SVNParentPath in default_auth.conf, but I just added that today as I was getting error messages as a result of adding the AuthzSVNAccessFile directive. With a totally permissive access file [/] joebloggs = rw the system worked fine (and was essentially unchanged), but as I soon as I start trying to add any kind of restrictions such as [sysadmin:/] joebloggs = rw instead, I get the 'Permission denied' errors again. The log file entries are: [Thu May 28 10:40:17 2009] [error] [client 89.100.219.180] Access denied: 'joebloggs' GET websvn:/ [Thu May 28 10:40:20 2009] [error] [client 89.100.219.180] Access denied: 'joebloggs' GET svn:/sysadmin What do I need to do to get this to work? Have configured apache wrong, or is my understanding of the svnaccess.conf file incorrect? If I am going about this the wrong way, I have no particular attachment to my overall approach, so feel free to offer alternatives as well. UPDATE (20090528-1600): I attempted to implement this answer, but I still cannot get it to work properly. I know most of the configuration is correct, as I have added [/] joebloggs = rw at the start and 'joebloggs' then has all the correct access. When I try to go repository-specific though, doing something like [/] joebloggs = rw [sysadmin:/] mickmurphy = rw then I got a permission denied error for mickmurphy (joebloggs still works), with an error similar to what I already had previously [Thu May 28 10:40:20 2009] [error] [client 89.100.219.180] Access denied: 'mickmurphy' GET svn:/sysadmin Also, I forgot to explain previously that all my repositories are underneath /var/lib/svn/repository UPDATE (20090529-1245): Still no luck getting this to work, but all the signs seem to be pointing to the issue being with path-access control in subversion not working properly. My assumption is that I have not conf

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• Why is my cron daemon is being killed every few minutes? OpenVZ?

  - by user113215

  As of about a week ago, my cron daemon refuses to stay running. I'm using Debian 6. Running something like pgrep cron shows that the daemon isn't running. I start the service with service cron start or /etc/init.d/cron start and it launches, but it disappears from the running process list after a few minutes (varying anywhere between 1 - 30 minutes before the process is killed again). Using strace -f service cron start, I can see that the process is being killed for some reason: nanosleep({56, 0}, 0x7fffa7184c80) = 0 stat("crontabs", {st_mode=S_IFDIR|S_ISVTX|0730, st_size=4096, ...}) = 0 stat("/etc/crontab", {st_mode=S_IFREG|0644, st_size=1100, ...}) = 0 stat("/etc/cron.d", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 stat("/etc/cron.d/php5", {st_mode=S_IFREG|0644, st_size=475, ...}) = 0 stat("/etc/cron.d/anacron", {st_mode=S_IFREG|0644, st_size=244, ...}) = 0 rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0 rt_sigaction(SIGCHLD, NULL, {0x4036f0, [CHLD], SA_RESTORER|SA_RESTART, 0x2b0e8465f230}, 8) = 0 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0 nanosleep({60, 0}, <unfinished ...> +++ killed by SIGKILL +++ There's nothing relevant in /var/log/syslog, /var/log/messages, /var/log/auth.log, or /var/log/kern.log to explain why the the process is dying. The system has about 500 MB of free memory, and cat /proc/loadavg returns 0.10 0.21 0.45 so resources shouldn't be the issue. I also tried removing and reinstalling the cron package using apt-get. What else should I check? How do I find out what's killing my crond? Edit: I'm on a virtual machine under OpenVZ (and as such, I have no swap). With cron running, free -m reports: total used free shared buffers cached Mem: 1024 465 558 0 0 0 -/+ buffers/cache: 465 558 Swap: 0 0 0 My OpenVZ User Beancounters via cat /proc/user_beancounters: Version: 2.5 uid resource held maxheld barrier limit failcnt 172087: kmemsize 8275718 25561636 51200000 51200000 0 lockedpages 0 968 2048 2048 0 privvmpages 113442 266465 262200 262200 3740757 shmpages 788 4004 128000 128000 0 dummy 0 0 0 0 0 numproc 39 98 600 600 0 physpages 50521 208434 0 9223372036854775807 0 vmguarpages 0 0 512000 512000 0 oomguarpages 50521 208447 512000 512000 0 numtcpsock 7 323 4096 4096 0 numflock 7 64 2048 2048 0 numpty 1 4 32 32 0 numsiginfo 0 23 1024 1024 0 tcpsndbuf 137984 17878480 20480000 20480000 0 tcprcvbuf 114688 6983504 20480000 20480000 0 othersockbuf 162960 1074440 20480000 20480000 0 dgramrcvbuf 0 24208 10240000 10240000 0 numothersock 101 353 2048 2048 0 dcachesize 459171 747444 10240000 10240000 0 numfile 1010 4221 50000 50000 0 dummy 0 0 0 0 0 dummy 0 0 0 0 0 dummy 0 0 0 0 0 numiptent 39 424 2048 2048 0

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• How can I centralise MySQL data between 3 or more geographically separate servers?

  - by Andy Castles

  To explain the background to the question: We have a home-grown PHP application (for running online language-learning courses) running on a Linux server and using MySQL on localhost for saving user data (e.g. results of tests taken, marks of submitted work, time spent on different pages in the courses, etc). As we have students from different geographic locations we currently have 3 virtual servers hosted close to those locations (Spain, UK and Hong Kong) and users are added to the server closest to them (they access via different URLs, e.g. europe.domain.com, uk.domain.com and asia.domain.com). This works but is an administrative nightmare as we have to remember which server a particular user is on, and users can only connect to one server. We would like to somehow centralise the information so that all users are visible on any of the servers and users could connect to any of the 3 servers. The question is, what method should we use to implement this. It must be an issue that that lots of people have encountered but I haven't found anything conclusive after a fair bit of Googling around. The closest I have seen to solutions are: something like master-master replication, but I have read so many posts suggesting that this is not a good idea as things like auto_increment fields can break. circular replication, this sounded perfect but to quote from O'Reilly's High Performance MySQL, "In general, rings are brittle and best avoided" We're not against rewriting code in the application to make it work with whatever solution is required but I am not sure if replication is the correct thing to use. Thanks, Andy P.S. I should add that we experimented with writes to a central database and then using reads from a local database but the response time between the different servers for writing was pretty bad and it's also important that written data is available immediately for reading so if replication is too slow this could cause out-of-date data to be returned. Edit: I have been thinking about writing my own rudimentary replication script which would involve something like having each user given a server ID to say which is his "home server", e.g. users in asia would be marked as having the Hong Kong server as their own server. Then the replication scripts (which would be a PHP script set to run as a cron job reasonably frequently, e.g. every 15 minutes or so) would run independently on each of the servers in the system. They would go through the database and distribute any information about users with the "home server" set to the server that the script is running on to all of the other databases in the system. They would also need to suck new information which has been added to any of the other databases on the system where the "home server" flag is the server where the script is running. I would need to work out the details and build in the logic to deal with conflicts but I think it would be possible, however I wanted to make sure that there is not a correct solution for this already out there as it seems like it must be a problem that many people have already come across.

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• Apache2 return 404 for proxy requests before reaching WSGI

  - by Alejandro Mezcua

  I have a Django app running under Apache2 and mod_wsgi and, unfortunately, lots of requests trying to use the server as a proxy. The server is responding OK with 404 errors but the errors are generated by the Django (WSGI) app, which causes a high CPU usage. If I turn off the app and let Apache handle the response directly (send a 404), the CPU usage drops to almost 0 (mod_proxy is not enabled). Is there a way to configure Apache to respond directly to this kind of requests with an error before the request hits the WSGI app? I have seen that maybe mod_security would be an option, but I'd like to know if I can do it without it. EDIT. I'll explain it a bit more. In the logs I have lots of connections trying to use the server as a web proxy (e.g. connections like GET http://zzz.zzz/ HTTP/1.1 where zzz.zzz is an external domain, not mine). This requests are passed on to mod_wsgi which then return a 404 (as per my Django app). If I disable the app, as mod_proxy is disabled, Apache returns the error directly. What I'd finally like to do is prevent Apache from passing the request to the WSGI for invalid domains, that is, if the request is a proxy request, directly return the error and not execute the WSGI app. EDIT2. Here is the apache2 config, using VirtualHosts files in sites-enabled (i have removed email addresses and changed IPs to xxx, change the server alias to sample.sample.xxx). What I'd like is for Apache to reject any request that doesn't go to sample.sample.xxx with and error, that is, accept only relative requests to the server or fully qualified only to the actual ServerAlias. default: <VirtualHost *:80> ServerAdmin [email protected] ServerName X.X.X.X ServerAlias X.X.X.X DocumentRoot /var/www/default <Directory /> Options FollowSymLinks AllowOverride None </Directory> <Directory /var/www/> Options FollowSymLinks AllowOverride None Order allow,deny allow from all </Directory> ErrorDocument 404 "404" ErrorDocument 403 "403" ErrorDocument 500 "500" ErrorLog ${APACHE_LOG_DIR}/error.log LogLevel warn CustomLog ${APACHE_LOG_DIR}/access.log combined </VirtualHost> actual host: <VirtualHost *:80> ErrorDocument 404 "404" ErrorDocument 403 "403" ErrorDocument 500 "500" WSGIScriptAlias / /var/www/sample.sample.xxx/django.wsgi ServerAdmin [email protected] ServerAlias sample.sample.xxx ServerName sample.sample.xxx CustomLog /var/www/sample.sample.xxx/log/sample.sample.xxx-access.log combined Alias /robots.txt /var/www/sample.sample.xxx/static/robots.txt Alias /favicon.ico /var/www/sample.sample.xxx/static/favicon.ico AliasMatch ^/([^/]*\.css) /var/www/sample.sample.xxx/static/$1 Alias /static/ /var/www/sample.sample.xxx/static/ Alias /media/ /var/www/sample.sample.xxx/media/ <Directory /var/www/sample.sample.xxx/static/> Order deny,allow Allow from all </Directory> <Directory /var/www/sample.sample.xxx/media/> Order deny,allow Allow from all </Directory> </VirtualHost>

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• Dual booting Windows 7 & 8.1, using the Windows 8 Startup Options Menu, when Windows 8.1 is already installed and you want to add Windows 7

  - by Josh

  There are many excellent guides out there that explain how to dual-boot Windows 7 & 8. However, they are written for people starting with a Windows 7 installation and add a Windows 8 installation to separate partition. From what I'm reading, following this procedure will result in Windows 8 installing and configuring the Startup Options Menu with an option to boot Windows 7 & 8. However, in my situation I have a Windows 8.1 machine that I want to install Windows 7 on, and enable dual-boot, where I can use the Startup Options Menu to select the OS to boot. I haven't been able to determine how to do this. From everything I've been able to find, it looks like if I install Windows 7, it is going to take over the boot loader process, and I won't have access to the Windows 8 "Startup Options Menu." This answer suggests I boot to VHD, but notes a drawback: You can't do this if the C:\drive is encrypted using ANY encryption shceme. Be that BitLocker or 3rd party. The location of the .VHD file you are booting to must reside on an unencrypted volume. Well, that's a bummer, because that's exactly what I wanted to do--I wanted my Windows 7 partition to be encrypted, and my Windows 8 partition to also be encrypted. The idea being that when OS was booted, it was completely locked out from accessing data on the other OS's partition. At this point, I'm thinking my only option is to install Windows 7, and then re-install Windows 8, which will give me the dual-boot option... am I right? Or is there a way to make this work. I'm thinking that I would need to figure out a process like this: Configure the Windows Startup Options Menu with a "blank" entry for Windows 7, pointing to an empty partition Insert the Windows 7 installation media, install Windows 7, and somehow restrict it to that partition (i.e., prevent it from "taking over" from the Startup Options Menu" Is this possible, and if so, how can I accomplish this? My concern is that if I simply install Windows 7 to a separate partition, Windows 7 will take over the entire boot process and I won't be able to get to my Windows 8 installation any more.

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