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• Updating records with their subordinates via CTE or subquery

  - by Mike Jolley

  Let's say I have a table with the following columns: Employees Table employeeID int employeeName varchar(50) managerID int totalOrganization int managerID is referential to employeeID. totalOrganization is currently 0 for all records. I'd like to update totalOrganization on each row to the total number of employees under them. So with the following records: employeeID employeeName managerID totalOrganization 1 John Cruz NULL 0 2 Mark Russell 1 0 3 Alice Johnson 1 0 4 Juan Valdez 3 0 The query should update the totalOrganizations to: employeeID employeeName managerID totalOrganization 1 John Cruz NULL 3 2 Mark Russell 1 0 3 Alice Johnson 1 1 4 Juan Valdez 3 0 I know I can get somewhat of an org. chart using the following CTE: WITH OrgChart (employeeID, employeeName,managerID,level) AS ( SELECT employeeID,employeeName,0 as managerID,0 AS Level FROM Employees WHERE managerID IS NULL UNION ALL SELECT Employees.employeeID,Employees.employeeName,Employees.managerID,Level + 1 FROM Employees INNER JOIN OrgChart ON Employees.managerID = OrgChart.employeeID ) SELECT employeeID,employeeName,managerID, level FROM OrgChart; Is there any way to update the Employees table using a stored procedure rather than building some routine outside of SQL to parse through the data?

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• How to nest transactions nicely - &quot;begin transaction&quot; vs &quot;save transaction&quot; and SQL Server

  - by Brian Biales

  Do you write stored procedures that might be used by others?  And those others may or may not have already started a transaction?  And your SP does several things, but if any of them fail, you have to undo them all and return with a code indicating it failed? Well, I have written such code, and it wasn’t working right until I finally figured out how to handle the case when we are already in a transaction, as well as the case where the caller did not start a transaction.  When a problem occurred, my “ROLLBACK TRANSACTION” would roll back not just my nested transaction, but the caller’s transaction as well.  So when I tested the procedure stand-alone, it seemed to work fine, but when others used it, it would cause a problem if it had to rollback.  When something went wrong in my procedure, their entire transaction was rolled back.  This was not appreciated. Now, I knew one could "nest" transactions, but the technical documentation was very confusing.  And I still have not found the approach below documented anywhere.  So here is a very brief description of how I got it to work, I hope you find this helpful. My example is a stored procedure that must figure out on its own if the caller has started a transaction or not.  This can be done in SQL Server by checking the @@TRANCOUNT value.  If no BEGIN TRANSACTION has occurred yet, this will have a value of 0.  Any number greater than zero means that a transaction is in progress.  If there is no current transaction, my SP begins a transaction. But if a transaction is already in progress, my SP uses SAVE TRANSACTION and gives it a name.  SAVE TRANSACTION creates a “save point”.  Note that creating a save point has no effect on @@TRANCOUNT.  So my SP starts with something like this: DECLARE @startingTranCount int SET @startingTranCount = @@TRANCOUNT IF @startingTranCount > 0 SAVE TRANSACTION mySavePointName ELSE BEGIN TRANSACTION -- … Then, when ready to commit the changes, you only need to commit if we started the transaction ourselves: IF @startingTranCount = 0 COMMIT TRANSACTION And finally, to roll back just your changes so far: -- Roll back changes... IF @startingTranCount > 0 ROLLBACK TRANSACTION MySavePointName ELSE ROLLBACK TRANSACTION Here is some code that you can try that will demonstrate how the save points work inside a transaction. This sample code creates a temporary table, then executes selects and updates, documenting what is going on, then deletes the temporary table. if running in SQL Management Studio, set Query Results to: Text for best readability of the results. -- Create a temporary table to test with, we'll drop it at the end. CREATE TABLE #ATable( [Column_A] [varchar](5) NULL ) ON [PRIMARY] GO SET NOCOUNT ON -- Ensure just one row - delete all rows, add one DELETE #ATable -- Insert just one row INSERT INTO #ATable VALUES('000') SELECT 'Before TRANSACTION starts, value in table is: ' AS Note, * FROM #ATable SELECT @@trancount AS CurrentTrancount --insert into a values ('abc') UPDATE #ATable SET Column_A = 'abc' SELECT 'UPDATED without a TRANSACTION, value in table is: ' AS Note, * FROM #ATable BEGIN TRANSACTION SELECT 'BEGIN TRANSACTION, trancount is now ' AS Note, @@TRANCOUNT AS TranCount UPDATE #ATable SET Column_A = '123' SELECT 'Row updated inside TRANSACTION, value in table is: ' AS Note, * FROM #ATable SAVE TRANSACTION MySavepoint SELECT 'Save point MySavepoint created, transaction count now:' as Note, @@TRANCOUNT AS TranCount UPDATE #ATable SET Column_A = '456' SELECT 'Updated after MySavepoint created, value in table is: ' AS Note, * FROM #ATable SAVE TRANSACTION point2 SELECT 'Save point point2 created, transaction count now:' as Note, @@TRANCOUNT AS TranCount UPDATE #ATable SET Column_A = '789' SELECT 'Updated after point2 savepoint created, value in table is: ' AS Note, * FROM #ATable ROLLBACK TRANSACTION point2 SELECT 'Just rolled back savepoint "point2", value in table is: ' AS Note, * FROM #ATable ROLLBACK TRANSACTION MySavepoint SELECT 'Just rolled back savepoint "MySavepoint", value in table is: ' AS Note, * FROM #ATable SELECT 'Both save points were rolled back, transaction count still:' as Note, @@TRANCOUNT AS TranCount ROLLBACK TRANSACTION SELECT 'Just rolled back the entire transaction..., value in table is: ' AS Note, * FROM #ATable DROP TABLE #ATable The output should look like this: Note                                           Column_A ---------------------------------------------- -------- Before TRANSACTION starts, value in table is:  000 CurrentTrancount ---------------- 0 Note                                               Column_A -------------------------------------------------- -------- UPDATED without a TRANSACTION, value in table is:  abc Note                                 TranCount ------------------------------------ ----------- BEGIN TRANSACTION, trancount is now  1 Note                                                Column_A --------------------------------------------------- -------- Row updated inside TRANSACTION, value in table is:  123 Note                                                   TranCount ------------------------------------------------------ ----------- Save point MySavepoint created, transaction count now: 1 Note                                                   Column_A ------------------------------------------------------ -------- Updated after MySavepoint created, value in table is:  456 Note                                              TranCount ------------------------------------------------- ----------- Save point point2 created, transaction count now: 1 Note                                                        Column_A ----------------------------------------------------------- -------- Updated after point2 savepoint created, value in table is:  789 Note                                                     Column_A -------------------------------------------------------- -------- Just rolled back savepoint "point2", value in table is:  456 Note                                                          Column_A ------------------------------------------------------------- -------- Just rolled back savepoint "MySavepoint", value in table is:  123 Note                                                        TranCount ----------------------------------------------------------- ----------- Both save points were rolled back, transaction count still: 1 Note                                                            Column_A --------------------------------------------------------------- -------- Just rolled back the entire transaction..., value in table is:  abc

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• How do I include 2 tables in LocalStorage?

  - by Noor

  I've got a table that you can edit, and I've got a simple code saving that list when you're done with editing it. (the tables have the contenteditable on) The problem I've stumbled upon is that if I double click on enter, the table gets divided into two separate tables with the same ID. This causes the code I'm using to set the localStorage to only store one of the tables (I assume the first).. I've thought of different solutions and I wonder if someone could point out the pro's and con's (if the solutions even works that is). Make a loop that checks the page after tables and stores them into an array of localStorage-items.. I'd have to dynamically create a localStorage item for each table. Take the whole div that the tables are in, and store that in the localStorage, when a user revisits the page, the page checks after the items in storage and displays the whole divs. Any suggestions you have that can beat this :).. (but no cache, it has to be with the localStorage!) Thanks

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• XSLT 1.0 count element with the same value in an attribute, and show it

  - by Erick

  I have a variable containing: <col p1="Newman" p2="Paul"/> ... <col p1="Newman" p2="Paolo"/> <col p1="Newman" p2="Paul"/> i wold in output a table with in the first column the value of p2 and in the second the number of time it appear. For each value of p2 should i have only a row. <table> <tr><td>p2</td><td>num</td></tr> <tr><td>Pault</td><td>2</td> ... <tr><td>Paolo</td><td>1</td> </table>

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• Need some tips on my SQL script?

  - by Nano HE

  Hi I plan to create a tale to store the race result like this, Place RaceNumber Gender Name Result 12 0112 Male Mike Lee 1:32:40 16 0117 Female Rose Marry 2:20:40 I confused at the items type definiation. Q1.I am not sure the result can be set to varchar(32) or other type? Q2. and for racenumber, between int(11) and varchar(11), which one is better? Q3. Can I use `UNIQUE KEY` like my way? Q4. Do I need split name to firstName and lastName in my DB table? DROP TABLE IF EXISTS `race_result`; CREATE TABLE IF NOT EXISTS `race_result` ( `id` int(11) NOT NULL auto_increment, `racenumber` int(11) NOT NULL, `gender` enum('male','female') NOT NULL, `name` varchar(16) NOT NULL, `result` varchar(32) NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `racenumber` (`racenumber`,`id`) ) ENGINE=MyISAM AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 AUTO_INCREMENT=3;

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• How come jQuery can't remove this element?

  - by George Edison

  I have a table like this: <table id='inventory_table'> <tr id='no_items_avail'> <td> There are no items in the database. </td> </tr> </table> And I want to get rid of it with jQuery like this: $('#inventory_table tbody tr#no_items_avail').remove(); However it doesn't seem to be working at all. What am I doing wrong? Edit: Also, the row above was originally inserted into the DOM with another jQuery call: $('#inventory_table tbody').append("<tr id='no_items_avail'....... If that helps. And, running: alert($('#no_items_avail').text()); yields "There are no items in the database." as expected.

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• How do I include 2 tables in one LocalStorage item?

  - by Noor

  I've got a table that you can edit, and I've got a simple code saving that list when you're done with editing it. (the tables have the contenteditable on) The problem I've stumbled upon is that if I double click on enter, the table gets divided into two separate tables with the same ID. This causes the code I'm using to set the localStorage to only store one of the tables (I assume the first).. I've thought of different solutions and I wonder if someone could point out the pro's and con's (if the solutions even works that is). Make a loop that checks the page after tables and stores them into an array of localStorage-items.. I'd have to dynamically create a localStorage item for each table. Take the whole div that the tables are in, and store that in the localStorage, when a user revisits the page, the page checks after the items in storage and displays the whole divs. Any suggestions you have that can beat this :).. (but no cache, it has to be with the localStorage!) Thanks

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• Getting mysql row that doesn't conflict with another row

  - by user939951

  I have two tables that link together through an id one is "submit_moderate" and one is "submit_post" The "submit_moderate" table looks like this id moderated_by post 1 James 60 2 Alice 32 3 Tim 18 4 Michael 60 Im using a simple query to get data from the "submit_post" table according to the "submit_moderate" table. $get_posts = mysql_query("SELECT * FROM submit_moderate WHERE moderated_by!='$user'"); $user is the person who is signed in. Now my problem is when I run this query, with the user 'Michael' it will retrieve this 1 James 60 2 Alice 32 3 Tim 18 Now technically this is correct however I don't want to retrieve the first row because 60 is associated with Michael as well as James. Basically I don't want to retrieve that value '60'. I know why this is happening however I can't figure out how to do this. I appreciate any hints or advice I can get.

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• SQL Simple ORDER BY

  - by AeroDroid

  I'm new to SQL and I don't think this question should be hard to answer. I have a high-score table for a game that contains the columns name, score, and rank. I want to know how I can order the table by descending order each time a new score is added so the table can always stay ordered by score. I know this is the wrong way of doing this, but I hope this makes my point kind of clearer. UPDATE `HSTable`.`Highscores` ORDER BY `Highscores`.`score` DESC; What is the correct way of approaching this? One more thing, is there a way I can set it so that the ranking value always stays where it's suppose to be from the SQL, for example, 1st place is always at the top regardless the score? Thanks!

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• SQL: ATER COLUMN to shorter CHAR(n) type

  - by Rising Star

  I'm working with MS SQL SERVER 2003. I want to change a column in one of my tables to have fewer characters in the entries. This is identical to this question: http://stackoverflow.com/questions/2281336/altering-a-table-column-to-accept-more-characters except for the fact that I want fewer characters instead of more. I have a column in one of my tables that holds nine-digit entries. A developer previously working on the table mistakenly set the column to hold ten-digit entries. I need to change the type from CHAR(10) to CHAR(9). Following the instructions from the discussion linked above, I wrote the statement ALTER TABLE [MY_TABLE] ALTER COLUMN [MY_COLUMN] CHAR(9); This returns the error message "String or binary data would be truncated". I see that my nine-digit strings have a space appended to make them ten digits. How do I tell SQL Server to discard the extra space and convert my column to a CHAR(9) type?

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• How to change Zend_Db_Table name within a Model to insert in multiple tables

  - by jwhat

  Using Zend Framework, I've created a Model to insert a record into a database. My question is, after $this->insert($data) how can I switch the active table so that I can insert a record into another table? Here's my code so far: class Model_DbTable_Foo extends Zend_Db_Table_Abstract { protected $_name = 'foo'; public function addFoo($params) { $data = array( 'foo' => $params['foo'], ); $this->insert($data); $foo_id = $this->getAdapter()->lastInsertId(); $data2 = array( 'bar' => $params['bar'] ); // I need to change the Db Table name here. $this->insert($data2); $bar_id = $this->getAdapter()->lastInsertId(); } }

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• Information sent in an HTML form

  - by dedalo

  Hi, I've a HTML file that shows to the user the contents of a database (it is shown as a table). The user can choose one of the rows.When this is done the selection made by the user is sent to a servlet that will work with that information. Imagine that this servlet is going to look for files related to the information chosen by the user. What I'd like to do is to provide the user with the option of also choosing the number of files that are going to be looked for by the servlet. That way the user should be able to choose one of the rows shown in the table and should also be able of typing the numers of files that are to be looked for. So far I'm able to send to the servlet what the user chooses in the table, but I'd like to know if it is possible to attach to this information the number of files requested. Thanks

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• Compute column widths in a HTML-like manner (based on cell contents)

  - by cipak

  Hi, I have a grid of data that I want to export to RTF, PDF etc. using various (and not perfect) PHP converters/generators. What I am missing most is the HTML table automatic adjustment of column widths based on the lengths of strings in the cells (strings contain line breaks which complicate things a bit, as they should be preserved). I need an algorithm that, given the contents of the cells (plain text), a total width of the table and an average width of a character, would return a width for each column. I wouldn't want to reinvent the wheel if something is already available. Of course it can't be perfect if the font is variable width, but an approximation would do just fine. Or maybe it could have a configurable table with widths for each character. Any hint would be appreciated. Thank you.

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• MySQL searching using many 'like' operators: is there a better way?

  - by DrAgonmoray

  I have a page that gets all rows from a table in a database, then displays the rows in an HTML table. That works great, but now I want to implement a 'search' feature. There is a searchbox, and search-terms are separated by a space. I am going to make it search three fields for the search terms, 'make' 'model' and 'type.' These three fields are VARCHAR(30). Currently if I wanted to search using 3 terms (say 'cool' 'abc' and '123') my query would look something like this. SELECT * FROM table WHERE make LIKE '%cool%' OR make LIKE '%abc%' OR make LIKE '%123%' OR model LIKE '%cool%' OR model LIKE '%abc%' OR model LIKE '%123%' OR type LIKE '%cool%' OR type LIKE '%abc%' OR type LIKE '%123%' That looks really bad, and it will get even worse if there are more search terms or more fields to search. My question to you: is there a better way to search? If so, what?

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• Help with SQL query

  - by user154301

  Hello, I have list of DateTime values, and for each value I need to fetch something from the database. I would like to do this with one query. I know it's possible to pass a table (list) to the stored procedure, but Im not sure how to write the query itself. Let's say I have the following table: CREATE TABLE Shows( ShowId [int] NOT NULL, StartTime DateTime NOT NULL, EndTime DateTime NOT NULL ) and an array of dates DECLARE @myDateArray MyCustomDateArrayType Now, if I were fetching a single item, I would write a query like this: SELECT * FROM Shows WHERE StartTime > @ArrayItem and @ArrayItem < EndTime where @ArrayItem is an item from @myDateArray . But how do I formulate the query that would fetch the information for all array items? Thanks!

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• How can I use innerHTML without delete the before innerHTML?

  - by Mikelon85

  I want to convert an Array to a HTML table, but innerHTML deletes it writes before. Here is the code: <html><div id="tablaP"></div> function cargar2() { document.getElementById('tablaP').innerHTML= "<table>" var h=1 for (i=0;i<miArray.length;i++){ document.getElementById('tablaP').innerHTML = '<tr>' for (j=0;j<miArray[i].length;j++){ document.getElementById("tablaP").innerHTML = '<td><td>' } document.getElementById('tablaP').innerHTML = '</tr>' h++ } document.getElementById('tablaP').innerHTML = '</table>' }

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• MySQL pivot tables - covert rows to columns

  - by user2723490

  This is the structure of my table: Then I run a query SELECT `date`,`index_name`,`results` FROM `mst_ind` WHERE `index_name` IN ('MSCI EAFE Mid NR USD', 'Alerian MLP PR USD') AND `time_period`='M1' and get a table like How can I convert "index_name" rows to columns like: date | MSCI EAFE Mid NR USD | Alerian MLP PR USD etc In other words I need each column to represent an index and rows to represent date-result. I understand that MySQL doesn't have pivot table functions. What is the easiest way of doing this? I've tried this code, but it generates an error: SELECT `date`, MAX(IF(index_name = 'Alerian MLP PR USD' AND `time_period`='M1', results, NULL)) AS res1, MAX(IF(index_name = 'MSCI EAFE Mid NR USD' AND `time_period`='M1', results, NULL)) AS res2 FROM `mst_ind` GROUP BY `date I need to make the conversion on the query level - not PHP. Please suggest a nice and elegant solution. Thanks!

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• Home ADSL Modem Dropping Packets?

  - by Cody

  I know this is supposed to be a "pro" forum, but I'm hoping someone can help since my ISP isn't doing much to try and fix things. My ISP has given me a DSL modem / Router combo - a ADB / Pirelli P.DG A2100N and I have a 4096 / 767 kbps connection. I use it purely as modem and router, and have the wireless AP feature turned off. I run it to a Ubiquiti Networks Toughswitch and use a Ubiquiti UAP as the wireless access point - although I've ran tests directly wired to the router with nothing else connected, and still see the same issues. I've been having issues where latency suddenly spikes from 8ms to google.com to 250+ if someone does anything on the internet. If I run a speedtest or something, I can see latencies above 3000ms. Regularly when downloading something, even if the speed is throttled to , it can get random drops to 0kbps every few seconds. Online gaming is impossible because I notice the sudden lag-outs in the connection, and video streams or VoIP drop out as well - it's not at all consistent. I managed to find the password to my modem and I don't think I see anything wrong with the settings - but I looked for the logs and found this: Jun 6 17:10:30 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:10:30 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:10:31 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:10:40 user warn kernel: __ratelimit: 63 callbacks suppressed Jun 6 17:10:40 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:10:40 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:10:40 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:10:40 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:10:40 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:10:40 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:22 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:23 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:24 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:24 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:24 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:24 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:24 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:25 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:25 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:25 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:29 user warn kernel: __ratelimit: 15 callbacks suppressed Jun 6 17:11:29 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:29 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:30 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:11:30 user warn kernel: nf_conntrack: table full, dropping packet. Jun 6 17:55:26 user warn kernel: bcmxtmcfg: OAM loopback response not received on VCC 1.1.3 Jun 6 17:55:27 user warn kernel: bcmxtmcfg: OAM loopback response not received on VCC 1.1.4 So, as I understand it, it appears the router is dropping packets? If that's the case, is there anything in the config that I can change? Or should I buy a new router, a new modem, or both?

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• How to prevent samba from holding a file lock after a client disconnects?

  - by Jean-Francois Chevrette

  Here I have a Samba server (Debian 5.0) thats is configured to host Windows XP profiles. Clients connects to this server and work on their profiles directly on the samba share (the profile is not copied locally). Every now and then, a client may not shutdown properly and thus Windows does not free the file locks. When looking at the samba locking table, we can see that many files are still locked even though the client is not connected anymore. In our case, this seems to occur with lockfiles created by Mozilla Thunderbird and Firefox. Here's an example of the samba locking table: # smbstatus -L | grep DENY_ALL | head -n5 Pid Uid DenyMode Access R/W Oplock SharePath Name Time -------------------------------------------------------------------------------------------------- 15494 10345 DENY_ALL 0x3019f RDWR EXCLUSIVE+BATCH /home/CORP/user1 app.profile/user1.thunderbird/parent.lock Mon Nov 22 07:12:45 2010 18040 10454 DENY_ALL 0x3019f RDWR EXCLUSIVE+BATCH /home/CORP/user2 app.profile/user2.thunderbird/parent.lock Mon Nov 22 11:20:45 2010 26466 10056 DENY_ALL 0x3019f RDWR EXCLUSIVE+BATCH /home/CORP/user3 app.profile/user3.firefox/parent.lock Mon Nov 22 08:48:23 2010 We can see that the files were opened by Windows and imposed a DENY_ALL lock. Now when a client reconnects to this share and tries to open those files, samba says that they are locked and denies access. Is there any way to work around this situation or am I missing something? Edit: We would like to avoid disabling file locks on the samba server because there are good reasons to have those enabled.

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• Know more about Enqueue Deadlock Detection

  - by Liu Maclean(???)

  ??? ORACLE ALLSTAR???????????????????,??????? ???????enqueue lock?????????3 ??????,????????????????????????????ora-00060 dead lock??process???3s: SQL> select * from v$version; BANNER ---------------------------------------------------------------- Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bi PL/SQL Release 10.2.0.5.0 - Production CORE 10.2.0.5.0 Production TNS for Linux: Version 10.2.0.5.0 - Production NLSRTL Version 10.2.0.5.0 - Production SQL> select * from global_name; GLOBAL_NAME -------------------------------------------------------------------------------- www.oracledatabase12g.com PROCESS A: set timing on; update maclean1 set t1=t1+1; PROCESS B: update maclean2 set t1=t1+1; PROCESS A: update maclean2 set t1=t1+1; PROCESS B: update maclean1 set t1=t1+1; ??3s? PROCESS A ?? ERROR at line 1: ORA-00060: deadlock detected while waiting for resource Elapsed: 00:00:03.02 ????Process A????????????? 3s,?????????????,??????? ?????????? ???????: SQL> col name for a30 SQL> col value for a5 SQL> col DESCRIB for a50 SQL> set linesize 140 pagesize 1400 SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ 2 FROM SYS.x$ksppi x, SYS.x$ksppcv y 3 WHERE x.inst_id = USERENV ('Instance') 4 AND y.inst_id = USERENV ('Instance') 5 AND x.indx = y.indx 6 AND x.ksppinm='_enqueue_deadlock_scan_secs'; NAME VALUE DESCRIB ------------------------------ ----- -------------------------------------------------- _enqueue_deadlock_scan_secs 0 deadlock scan interval SQL> alter system set "_enqueue_deadlock_scan_secs"=18 scope=spfile; System altered. Elapsed: 00:00:00.01 SQL> startup force; ORACLE instance started. Total System Global Area 851443712 bytes Fixed Size 2100040 bytes Variable Size 738198712 bytes Database Buffers 104857600 bytes Redo Buffers 6287360 bytes Database mounted. Database opened. PROCESS A: SQL> set timing on; SQL> update maclean1 set t1=t1+1; 1 row updated. Elapsed: 00:00:00.06 Process B SQL> update maclean2 set t1=t1+1; 1 row updated. SQL> update maclean1 set t1=t1+1; Process A: SQL> SQL> alter session set events '10704 trace name context forever,level 10:10046 trace name context forever,level 8'; Session altered. SQL> update maclean2 set t1=t1+1; update maclean2 set t1=t1+1 * ERROR at line 1: ORA-00060: deadlock detected while waiting for resource  Elapsed: 00:00:18.05 ksqcmi: TX,90011,4a9 mode=6 timeout=21474836 WAIT #12: nam='enq: TX - row lock contention' ela= 2930070 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114759849120 WAIT #12: nam='enq: TX - row lock contention' ela= 2930636 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114762779801 WAIT #12: nam='enq: TX - row lock contention' ela= 2930439 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114765710430 *** 2012-06-12 09:58:43.089 WAIT #12: nam='enq: TX - row lock contention' ela= 2931698 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114768642192 WAIT #12: nam='enq: TX - row lock contention' ela= 2930428 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114771572755 WAIT #12: nam='enq: TX - row lock contention' ela= 2931408 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114774504207 DEADLOCK DETECTED ( ORA-00060 ) [Transaction Deadlock] The following deadlock is not an ORACLE error. It is a deadlock due to user error in the design of an application or from issuing incorrect ad-hoc SQL. The following information may aid in determining the deadlock: ??????Process A?’enq: TX – row lock contention’ ?????ORA-00060 deadlock detected????3s ??? 18s , ???hidden parameter “_enqueue_deadlock_scan_secs”?????,????????0? ??????????: SQL> alter system set "_enqueue_deadlock_scan_secs"=4 scope=spfile; System altered. Elapsed: 00:00:00.01 SQL> alter system set "_enqueue_deadlock_time_sec"=9 scope=spfile; System altered. Elapsed: 00:00:00.00 SQL> startup force; ORACLE instance started. Total System Global Area 851443712 bytes Fixed Size 2100040 bytes Variable Size 738198712 bytes Database Buffers 104857600 bytes Redo Buffers 6287360 bytes Database mounted. Database opened. SQL> set linesize 140 pagesize 1400 SQL> show parameter dead NAME TYPE VALUE ------------------------------------ -------------------------------- ------------------------------ _enqueue_deadlock_scan_secs integer 4 _enqueue_deadlock_time_sec integer 9 SQL> set timing on SQL> select * from maclean1 for update wait 8; T1 ---------- 11 Elapsed: 00:00:00.01 PROCESS B SQL> select * from maclean2 for update wait 8; T1 ---------- 3 SQL> select * from maclean1 for update wait 8; select * from maclean1 for update wait 8 PROCESS A SQL> select * from maclean2 for update wait 8; select * from maclean2 for update wait 8 * ERROR at line 1: ORA-30006: resource busy; acquire with WAIT timeout expired Elapsed: 00:00:08.00 ???????? ??? select for update wait?enqueue request timeout ?????8s? ,???????”_enqueue_deadlock_scan_secs”=4(deadlock scan interval),?4s???deadlock detected,????Process A????deadlock ???, ??????? ??Process A?????8s?raised??”ORA-30006: resource busy; acquire with WAIT timeout expired”??,??ORA-00060,?????process A???????? ????????”_enqueue_deadlock_time_sec”(requests with timeout <= this will not have deadlock detection)???,?enqueue request time < “_enqueue_deadlock_time_sec”?Server process?????dead lock detection,?????????enqueue request ??????timeout??????(_enqueue_deadlock_time_sec????5,?timeout<5s),???????????????;??????timeout>”_enqueue_deadlock_time_sec”???,Oracle????????????????????? ??????????: SQL> show parameter dead NAME TYPE VALUE ------------------------------------ -------------------------------- ------------------------------ _enqueue_deadlock_scan_secs integer 4 _enqueue_deadlock_time_sec integer 9 Process A: SQL> set timing on; SQL> select * from maclean1 for update wait 10; T1 ---------- 11 Process B: SQL> select * from maclean2 for update wait 10; T1 ---------- 3 SQL> select * from maclean1 for update wait 10; PROCESS A: SQL> select * from maclean2 for update wait 10; select * from maclean2 for update wait 10 * ERROR at line 1: ORA-00060: deadlock detected while waiting for resource Elapsed: 00:00:06.02 ??????? select for update wait 10?10s??, ?? 10s?????_enqueue_deadlock_time_sec???(9s),??Process A???????? ???????????????6s ???????_enqueue_deadlock_scan_secs?4s ? ???????????,???????????_enqueue_deadlock_scan_secs?????????3???? ??: enqueue lock?????????????? 1. ?????????deadlock detection??3s????, ????????_enqueue_deadlock_scan_secs(deadlock scan interval)???,??????0,????????_enqueue_deadlock_scan_secs?????????3???, ?_enqueue_deadlock_scan_secs=0 ??3s??, ?_enqueue_deadlock_scan_secs=4??6s??,????? 2. ???????_enqueue_deadlock_time_sec(requests with timeout <= this will not have deadlock detection)???,?enqueue request timeout< _enqueue_deadlock_time_sec(????5),?Server process?????????enqueue request timeout>_enqueue_deadlock_time_sec ????_enqueue_deadlock_scan_secs???????, ??request timeout??????select for update wait [TIMEOUT]??? ??: ???10.2.0.1?????????2?hidden parameter , ???patchset 10.2.0.3????? _enqueue_deadlock_time_sec, ?patchset 10.2.0.5??????_enqueue_deadlock_scan_secs? ?????RAC???????????10s, ???????_lm_dd_interval(dd time interval in seconds) ,????????8.0.6???? ???????????????,??????,  ?10g???????60s,?11g???????10s?  ???????11g??_lm_dd_interval?????????????,?????11g??LMD????????????,??????????RAC?LMD?Deadlock Detection???????CPU,???11g?Oracle????Team???LMD????????CPU????: ????????11g?LMD???????,???????11g??? UTS TRACE ????? DD???: SQL> select * from v$version; BANNER -------------------------------------------------------------------------------- Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production PL/SQL Release 11.2.0.3.0 - Production CORE 11.2.0.3.0 Production TNS for Linux: Version 11.2.0.3.0 - Production NLSRTL Version 11.2.0.3.0 - Production SQL> SQL> select * from global_name 2 ; GLOBAL_NAME -------------------------------------------------------------------------------- www.oracledatabase12g.com SQL> alter system set "_lm_dd_interval"=20 scope=spfile; System altered. SQL> startup force; ORACLE instance started. Total System Global Area 1570009088 bytes Fixed Size 2228704 bytes Variable Size 1325403680 bytes Database Buffers 234881024 bytes Redo Buffers 7495680 bytes Database mounted. Database opened. SQL> set linesize 140 pagesize 1400 SQL> show parameter lm_dd NAME TYPE VALUE ------------------------------------ -------------------------------- ------------------------------ _lm_dd_interval integer 20 SQL> select count(*) from gv$instance; COUNT(*) ---------- 2 instance 1: SQL> oradebug setorapid 12 Oracle pid: 12, Unix process pid: 8608, image: [email protected] (LMD0) ? LMD0??? UTS TRACE??RAC???????????? SQL> oradebug event 10046 trace name context forever,level 8:10708 trace name context forever,level 103: trace[rac.*] disk high; Statement processed. Elapsed: 00:00:00.00 SQL> update maclean1 set t1=t1+1; 1 row updated. instance 2: SQL> update maclean2 set t1=t1+1; 1 row updated. SQL> update maclean1 set t1=t1+1; Instance 1: SQL> update maclean2 set t1=t1+1; update maclean2 set t1=t1+1 * ERROR at line 1: ORA-00060: deadlock detected while waiting for resource Elapsed: 00:00:20.51 LMD0???UTS TRACE 2012-06-12 22:27:00.929284 : [kjmpbmsg:process][type 22][msg 0x7fa620ac85a8][from 1][seq 8148.0][len 192] 2012-06-12 22:27:00.929346 : [kjmxmpm][type 22][seq 0.0][msg 0x7fa620ac85a8][from 1] *** 2012-06-12 22:27:00.929 * kjddind: received DDIND msg with subtype x6 * reqp->dd_master_inst_kjxmddi == 1 * kjddind: dump sgh: 2012-06-12 22:27:00.929346*: kjddind: req->timestamp [0.15], kjddt [0.13] 2012-06-12 22:27:00.929346*: >> DDmsg:KJX_DD_REMOTE,TS[0.15],Inst 1->2,ddxid[id1,id2,inst:2097153,31,1],ddlock[0x95023930,829],ddMasterInst 1 2012-06-12 22:27:00.929346*: lock [0x95023930,829], op = [mast] 2012-06-12 22:27:00.929346*: reqp->timestamp [0.15], kjddt [0.13] 2012-06-12 22:27:00.929346*: kjddind: updated local timestamp [0.15] * kjddind: case KJX_DD_REMOTE 2012-06-12 22:27:00.929346*: ADD IO NODE WFG: 0 frame pointer 2012-06-12 22:27:00.929346*: PUSH: type=res, enqueue(0xffffffff.0xffffffff)=0xbbb9af40, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: PROCESS: type=res, enqueue(0xffffffff.0xffffffff)=0xbbb9af40, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: POP: type=res, enqueue(0xffffffff.0xffffffff)=0xbbb9af40, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: kjddopr[TX 0xe000c.0x32][ext 0x5,0x0]: blocking lock 0xbbb9a800, owner 2097154 of inst 2 2012-06-12 22:27:00.929346*: PUSH: type=txn, enqueue(0xffffffff.0xffffffff)=0xbbb9a800, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: PROCESS: type=txn, enqueue(0xffffffff.0xffffffff)=0xbbb9a800, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: ADD NODE TO WFG: type=txn, enqueue(0xffffffff.0xffffffff)=0xbbb9a800, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: POP: type=txn, enqueue(0xffffffff.0xffffffff)=0xbbb9a800, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: kjddopt: converting lock 0xbbce92f8 on 'TX' 0x80016.0x5d4,txid [2097154,34]of inst 2 2012-06-12 22:27:00.929346*: PUSH: type=res, enqueue(0xffffffff.0xffffffff)=0xbbce92f8, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: PROCESS: type=res, enqueue(0xffffffff.0xffffffff)=0xbbce92f8, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: ADD NODE TO WFG: type=res, enqueue(0xffffffff.0xffffffff)=0xbbce92f8, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929855 : GSIPC:AMBUF: rcv buff 0x7fa620aa8cd8, pool rcvbuf, rqlen 1102 2012-06-12 22:27:00.929878 : GSIPC:GPBMSG: new bmsg 0x7fa620aa8d48 mb 0x7fa620aa8cd8 msg 0x7fa620aa8d68 mlen 192 dest x100 flushsz -1 2012-06-12 22:27:00.929878*: << DDmsg:KJX_DD_REMOTE,TS[0.15],Inst 2->1,ddxid[id1,id2,inst:2097153,31,1],ddlock[0x95023930,829],ddMasterInst 1 2012-06-12 22:27:00.929878*: lock [0xbbce92f8,287], op = [mast] 2012-06-12 22:27:00.929878*: ADD IO NODE WFG: 0 frame pointer 2012-06-12 22:27:00.929923 : [kjmpbmsg:compl][msg 0x7fa620ac8588][typ p][nmsgs 1][qtime 0][ptime 0] 2012-06-12 22:27:00.929947 : GSIPC:PBAT: flush start. flag 0x79 end 0 inc 4.4 2012-06-12 22:27:00.929963 : GSIPC:PBAT: send bmsg 0x7fa620aa8d48 blen 224 dest 1.0 2012-06-12 22:27:00.929979 : GSIPC:SNDQ: enq msg 0x7fa620aa8d48, type 65521 seq 8325, inst 1, receiver 0, queued 1 012-06-12 22:27:00.929979 : GSIPC:SNDQ: enq msg 0x7fa620aa8d48, type 65521 seq 8325, inst 1, receiver 0, queued 1 2012-06-12 22:27:00.929996 : GSIPC:BSEND: flushing sndq 0xb491dd28, id 0, dcx 0xbc517770, inst 1, rcvr 0 qlen 0 1 2012-06-12 22:27:00.930014 : GSIPC:BSEND: no batch1 msg 0x7fa620aa8d48 type 65521 len 224 dest (1:0) 2012-06-12 22:27:00.930088 : kjbsentscn[0x0.3f72dc][to 1] 2012-06-12 22:27:00.930144 : GSIPC:SENDM: send msg 0x7fa620aa8d48 dest x10000 seq 8325 type 65521 tkts x1 mlen xe00110 2012-06-12 22:27:00.930531 : GSIPC:KSXPCB: msg 0x7fa620aa8d48 status 30, type 65521, dest 1, rcvr 0 WAIT #0: nam='ges remote message' ela= 1372 waittime=80 loop=0 p3=74 obj#=-1 tim=1339554420931640 2012-06-12 22:27:00.931728 : GSIPC:RCVD: ksxp msg 0x7fa620af6490 sndr 1 seq 0.8149 type 65521 tkts 1 2012-06-12 22:27:00.931746 : GSIPC:RCVD: watq msg 0x7fa620af6490 sndr 1, seq 8149, type 65521, tkts 1 2012-06-12 22:27:00.931763 : GSIPC:RCVD: seq update (0.8148)->(0.8149) tp -15 fg 0x4 from 1 pbattr 0x0 2012-06-12 22:27:00.931779 : GSIPC:TKT: collect msg 0x7fa620af6490 from 1 for rcvr 0, tickets 1 2012-06-12 22:27:00.931794 : kjbrcvdscn[0x0.3f72dc][from 1][idx 2012-06-12 22:27:00.931810 : kjbrcvdscn[no bscn dd_master_inst_kjxmddi == 1 * kjddind: dump sgh: NXTIN (nil) 0 wq 0 cvtops x0 0x0.0x0(ext 0x0,0x0)[0000-0000-00000000] inst 1 BLOCKER 0xbbb9a800 5 wq 1 cvtops x28 TX 0xe000c.0x32(ext 0x5,0x0)[20000-0002-00000022] inst 2 BLOCKED 0xbbce92f8 5 wq 2 cvtops x1 TX 0x80016.0x5d4(ext 0x2,0x0)[20000-0002-00000022] inst 2 NXTOUT (nil) 0 wq 0 cvtops x0 0x0.0x0(ext 0x0,0x0)[0000-0000-00000000] inst 1 2012-06-12 22:27:00.932058*: kjddind: req->timestamp [0.15], kjddt [0.15] 2012-06-12 22:27:00.932058*: >> DDmsg:KJX_DD_VALIDATE,TS[0.15],Inst 1->2,ddxid[id1,id2,inst:2097153,31,1],ddlock[0x95023930,829],ddMasterInst 1 2012-06-12 22:27:00.932058*: lock [(nil),0], op = [vald_dd] 2012-06-12 22:27:00.932058*: kjddind: updated local timestamp [0.15] * kjddind: case KJX_DD_VALIDATE *** 2012-06-12 22:27:00.932 * kjddvald called: kjxmddi stuff: * cont_lockp (nil) * dd_lockp 0x95023930 * dd_inst 1 * dd_master_inst 1 * sgh graph: NXTIN (nil) 0 wq 0 cvtops x0 0x0.0x0(ext 0x0,0x0)[0000-0000-00000000] inst 1 BLOCKER 0xbbb9a800 5 wq 1 cvtops x28 TX 0xe000c.0x32(ext 0x5,0x0)[20000-0002-00000022] inst 2 BLOCKED 0xbbce92f8 5 wq 2 cvtops x1 TX 0x80016.0x5d4(ext 0x2,0x0)[20000-0002-00000022] inst 2 NXTOUT (nil) 0 wq 0 cvtops x0 0x0.0x0(ext 0x0,0x0)[0000-0000-00000000] inst 1 POP WFG NODE: lock=(nil) * kjddvald: dump the PRQ: BLOCKER 0xbbb9a800 5 wq 1 cvtops x28 TX 0xe000c.0x32(ext 0x5,0x0)[20000-0002-00000022] inst 2 BLOCKED 0xbbce92f8 5 wq 2 cvtops x1 TX 0x80016.0x5d4(ext 0x2,0x0)[20000-0002-00000022] inst 2 * kjddvald: KJDD_NXTONOD ->node_kjddsg.dinst_kjddnd =1 * kjddvald: ... which is not my node, my subgraph is validated but the cycle is not complete Global blockers dump start:--------------------------------- DUMP LOCAL BLOCKER/HOLDER: block level 5 res [0x80016][0x5d4],[TX][ext 0x2,0x0] ??dead lock!!! ???????11.2.0.3???? RAC LMD???????????”_lm_dd_interval”????????????20s?  ???????10g?_lm_dd_interval???60s,??????Processes?????????????????,????????????Server Process????????60s??????11g?????(??????LMD???????)???????,???????????10s??? Enqueue Deadlock Detection? ?11g??? RAC?LMD???????hidden parameter ????”_lm_dd_interval”???,RAC????????????????,???????????: SQL> col name for a50 SQL> col describ for a60 SQL> col value for a20 SQL> set linesize 140 pagesize 1400 SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ 2 FROM SYS.x$ksppi x, SYS.x$ksppcv y 3 WHERE x.inst_id = USERENV ('Instance') 4 AND y.inst_id = USERENV ('Instance') 5 AND x.indx = y.indx 6 AND x.ksppinm like '_lm_dd%'; NAME VALUE DESCRIB -------------------------------------------------- -------------------- ------------------------------------------------------------ _lm_dd_interval 20 dd time interval in seconds _lm_dd_scan_interval 5 dd scan interval in seconds _lm_dd_search_cnt 3 number of dd search per token get _lm_dd_max_search_time 180 max dd search time per token _lm_dd_maxdump 50 max number of locks to be dumped during dd validation _lm_dd_ignore_nodd FALSE if TRUE nodeadlockwait/nodeadlockblock options are ignored 6 rows selected.

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• .NET Code Evolution

  - by Alois Kraus

  Originally posted on: http://geekswithblogs.net/akraus1/archive/2013/07/24/153504.aspxAt my day job I do look at a lot of code written by other people. Most of the code is quite good and some is even a masterpiece. And there is also code which makes you think WTF… oh it was written by me. Hm not so bad after all. There are many excuses reasons for bad code. Most often it is time pressure followed by not enough ambition (who cares) or insufficient training. Normally I do care about code quality quite a lot which makes me a (perceived) slow worker who does write many tests and refines the code quite a lot because of the design deficiencies. Most of the deficiencies I do find by putting my design under stress while checking for invariants. It does also help a lot to step into the code with a debugger (sometimes also Windbg). I do this much more often when my tests are red. That way I do get a much better understanding what my code really does and not what I think it should be doing. This time I do want to show you how code can evolve over the years with different .NET Framework versions. Once there was  time where .NET 1.1 was new and many C++ programmers did switch over to get rid of not initialized pointers and memory leaks. There were also nice new data structures available such as the Hashtable which is fast lookup table with O(1) time complexity. All was good and much code was written since then. At 2005 a new version of the .NET Framework did arrive which did bring many new things like generics and new data structures. The “old” fashioned way of Hashtable were coming to an end and everyone used the new Dictionary<xx,xx> type instead which was type safe and faster because the object to type conversion (aka boxing) was no longer necessary. I think 95% of all Hashtables and dictionaries use string as key. Often it is convenient to ignore casing to make it easy to look up values which the user did enter. An often followed route is to convert the string to upper case before putting it into the Hashtable. Hashtable Table = new Hashtable(); void Add(string key, string value) { Table.Add(key.ToUpper(), value); } This is valid and working code but it has problems. First we can pass to the Hashtable a custom IEqualityComparer to do the string matching case insensitive. Second we can switch over to the now also old Dictionary type to become a little faster and we can keep the the original keys (not upper cased) in the dictionary. Dictionary<string, string> DictTable = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase); void AddDict(string key, string value) { DictTable.Add(key, value); } Many people do not user the other ctors of Dictionary because they do shy away from the overhead of writing their own comparer. They do not know that .NET has for strings already predefined comparers at hand which you can directly use. Today in the many core area we do use threads all over the place. Sometimes things break in subtle ways but most of the time it is sufficient to place a lock around the offender. Threading has become so mainstream that it may sound weird that in the year 2000 some guy got a huge incentive for the idea to reduce the time to process calibration data from 12 hours to 6 hours by using two threads on a dual core machine. Threading does make it easy to become faster at the expense of correctness. Correct and scalable multithreading can be arbitrarily hard to achieve depending on the problem you are trying to solve. Lets suppose we want to process millions of items with two threads and count the processed items processed by all threads. A typical beginners code might look like this: int Counter; void IJustLearnedToUseThreads() { var t1 = new Thread(ThreadWorkMethod); t1.Start(); var t2 = new Thread(ThreadWorkMethod); t2.Start(); t1.Join(); t2.Join(); if (Counter != 2 * Increments) throw new Exception("Hmm " + Counter + " != " + 2 * Increments); } const int Increments = 10 * 1000 * 1000; void ThreadWorkMethod() { for (int i = 0; i < Increments; i++) { Counter++; } } It does throw an exception with the message e.g. “Hmm 10.222.287 != 20.000.000” and does never finish. The code does fail because the assumption that Counter++ is an atomic operation is wrong. The ++ operator is just a shortcut for Counter = Counter + 1 This does involve reading the counter from a memory location into the CPU, incrementing value on the CPU and writing the new value back to the memory location. When we do look at the generated assembly code we will see only inc dword ptr [ecx+10h] which is only one instruction. Yes it is one instruction but it is not atomic. All modern CPUs have several layers of caches (L1,L2,L3) which try to hide the fact how slow actual main memory accesses are. Since cache is just another word for redundant copy it can happen that one CPU does read a value from main memory into the cache, modifies it and write it back to the main memory. The problem is that at least the L1 cache is not shared between CPUs so it can happen that one CPU does make changes to values which did change in meantime in the main memory. From the exception you can see we did increment the value 20 million times but half of the changes were lost because we did overwrite the already changed value from the other thread. This is a very common case and people do learn to protect their  data with proper locking.   void Intermediate() { var time = Stopwatch.StartNew(); Action acc = ThreadWorkMethod_Intermediate; var ar1 = acc.BeginInvoke(null, null); var ar2 = acc.BeginInvoke(null, null); ar1.AsyncWaitHandle.WaitOne(); ar2.AsyncWaitHandle.WaitOne(); if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Intermediate did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Intermediate() { for (int i = 0; i < Increments; i++) { lock (this) { Counter++; } } } This is better and does use the .NET Threadpool to get rid of manual thread management. It does give the expected result but it can result in deadlocks because you do lock on this. This is in general a bad idea since it can lead to deadlocks when other threads use your class instance as lock object. It is therefore recommended to create a private object as lock object to ensure that nobody else can lock your lock object. When you read more about threading you will read about lock free algorithms. They are nice and can improve performance quite a lot but you need to pay close attention to the CLR memory model. It does make quite weak guarantees in general but it can still work because your CPU architecture does give you more invariants than the CLR memory model. For a simple counter there is an easy lock free alternative present with the Interlocked class in .NET. As a general rule you should not try to write lock free algos since most likely you will fail to get it right on all CPU architectures. void Experienced() { var time = Stopwatch.StartNew(); Task t1 = Task.Factory.StartNew(ThreadWorkMethod_Experienced); Task t2 = Task.Factory.StartNew(ThreadWorkMethod_Experienced); t1.Wait(); t2.Wait(); if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Experienced did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Experienced() { for (int i = 0; i < Increments; i++) { Interlocked.Increment(ref Counter); } } Since time does move forward we do not use threads explicitly anymore but the much nicer Task abstraction which was introduced with .NET 4 at 2010. It is educational to look at the generated assembly code. The Interlocked.Increment method must be called which does wondrous things right? Lets see: lock inc dword ptr [eax] The first thing to note that there is no method call at all. Why? Because the JIT compiler does know very well about CPU intrinsic functions. Atomic operations which do lock the memory bus to prevent other processors to read stale values are such things. Second: This is the same increment call prefixed with a lock instruction. The only reason for the existence of the Interlocked class is that the JIT compiler can compile it to the matching CPU intrinsic functions which can not only increment by one but can also do an add, exchange and a combined compare and exchange operation. But be warned that the correct usage of its methods can be tricky. If you try to be clever and look a the generated IL code and try to reason about its efficiency you will fail. Only the generated machine code counts. Is this the best code we can write? Perhaps. It is nice and clean. But can we make it any faster? Lets see how good we are doing currently. Level Time in s IJustLearnedToUseThreads Flawed Code Intermediate 1,5 (lock) Experienced 0,3 (Interlocked.Increment) Master 0,1 (1,0 for int[2]) That lock free thing is really a nice thing. But if you read more about CPU cache, cache coherency, false sharing you can do even better. int[] Counters = new int[12]; // Cache line size is 64 bytes on my machine with an 8 way associative cache try for yourself e.g. 64 on more modern CPUs void Master() { var time = Stopwatch.StartNew(); Task t1 = Task.Factory.StartNew(ThreadWorkMethod_Master, 0); Task t2 = Task.Factory.StartNew(ThreadWorkMethod_Master, Counters.Length - 1); t1.Wait(); t2.Wait(); Counter = Counters[0] + Counters[Counters.Length - 1]; if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Master did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Master(object number) { int index = (int) number; for (int i = 0; i < Increments; i++) { Counters[index]++; } } The key insight here is to use for each core its own value. But if you simply use simply an integer array of two items, one for each core and add the items at the end you will be much slower than the lock free version (factor 3). Each CPU core has its own cache line size which is something in the range of 16-256 bytes. When you do access a value from one location the CPU does not only fetch one value from main memory but a complete cache line (e.g. 16 bytes). This means that you do not pay for the next 15 bytes when you access them. This can lead to dramatic performance improvements and non obvious code which is faster although it does have many more memory reads than another algorithm. So what have we done here? We have started with correct code but it was lacking knowledge how to use the .NET Base Class Libraries optimally. Then we did try to get fancy and used threads for the first time and failed. Our next try was better but it still had non obvious issues (lock object exposed to the outside). Knowledge has increased further and we have found a lock free version of our counter which is a nice and clean way which is a perfectly valid solution. The last example is only here to show you how you can get most out of threading by paying close attention to your used data structures and CPU cache coherency. Although we are working in a virtual execution environment in a high level language with automatic memory management it does pay off to know the details down to the assembly level. Only if you continue to learn and to dig deeper you can come up with solutions no one else was even considering. I have studied particle physics which does help at the digging deeper part. Have you ever tried to solve Quantum Chromodynamics equations? Compared to that the rest must be easy ;-). Although I am no longer working in the Science field I take pride in discovering non obvious things. This can be a very hard to find bug or a new way to restructure data to make something 10 times faster. Now I need to get some sleep ….

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• Utility that helps in file locking - expert tips wanted

  - by maix

  I've written a subclass of file that a) provides methods to conveniently lock it (using fcntl, so it only supports unix, which is however OK for me atm) and b) when reading or writing asserts that the file is appropriately locked. Now I'm not an expert at such stuff (I've just read one paper [de] about it) and would appreciate some feedback: Is it secure, are there race conditions, are there other things that could be done better … Here is the code: from fcntl import flock, LOCK_EX, LOCK_SH, LOCK_UN, LOCK_NB class LockedFile(file): """ A wrapper around `file` providing locking. Requires a shared lock to read and a exclusive lock to write. Main differences: * Additional methods: lock_ex, lock_sh, unlock * Refuse to read when not locked, refuse to write when not locked exclusivly. * mode cannot be `w` since then the file would be truncated before it could be locked. You have to lock the file yourself, it won't be done for you implicitly. Only you know what lock you need. Example usage:: def get_config(): f = LockedFile(CONFIG_FILENAME, 'r') f.lock_sh() config = parse_ini(f.read()) f.close() def set_config(key, value): f = LockedFile(CONFIG_FILENAME, 'r+') f.lock_ex() config = parse_ini(f.read()) config[key] = value f.truncate() f.write(make_ini(config)) f.close() """ def __init__(self, name, mode='r', *args, **kwargs): if 'w' in mode: raise ValueError('Cannot open file in `w` mode') super(LockedFile, self).__init__(name, mode, *args, **kwargs) self.locked = None def lock_sh(self, **kwargs): """ Acquire a shared lock on the file. If the file is already locked exclusively, do nothing. :returns: Lock status from before the call (one of 'sh', 'ex', None). :param nonblocking: Don't wait for the lock to be available. """ if self.locked == 'ex': return # would implicitly remove the exclusive lock return self._lock(LOCK_SH, **kwargs) def lock_ex(self, **kwargs): """ Acquire an exclusive lock on the file. :returns: Lock status from before the call (one of 'sh', 'ex', None). :param nonblocking: Don't wait for the lock to be available. """ return self._lock(LOCK_EX, **kwargs) def unlock(self): """ Release all locks on the file. Flushes if there was an exclusive lock. :returns: Lock status from before the call (one of 'sh', 'ex', None). """ if self.locked == 'ex': self.flush() return self._lock(LOCK_UN) def _lock(self, mode, nonblocking=False): flock(self, mode | bool(nonblocking) * LOCK_NB) before = self.locked self.locked = {LOCK_SH: 'sh', LOCK_EX: 'ex', LOCK_UN: None}[mode] return before def _assert_read_lock(self): assert self.locked, "File is not locked" def _assert_write_lock(self): assert self.locked == 'ex', "File is not locked exclusively" def read(self, *args): self._assert_read_lock() return super(LockedFile, self).read(*args) def readline(self, *args): self._assert_read_lock() return super(LockedFile, self).readline(*args) def readlines(self, *args): self._assert_read_lock() return super(LockedFile, self).readlines(*args) def xreadlines(self, *args): self._assert_read_lock() return super(LockedFile, self).xreadlines(*args) def __iter__(self): self._assert_read_lock() return super(LockedFile, self).__iter__() def next(self): self._assert_read_lock() return super(LockedFile, self).next() def write(self, *args): self._assert_write_lock() return super(LockedFile, self).write(*args) def writelines(self, *args): self._assert_write_lock() return super(LockedFile, self).writelines(*args) def flush(self): self._assert_write_lock() return super(LockedFile, self).flush() def truncate(self, *args): self._assert_write_lock() return super(LockedFile, self).truncate(*args) def close(self): self.unlock() return super(LockedFile, self).close() (the example in the docstring is also my current use case for this) Thanks for having read until down here, and possibly even answering :)

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• Mysql: Order Results by number of matching rows in Second Table.

  - by KyleT

  I'm not sure the best way to word this question so bear with me. Table A has following columns: id name description Table B has the following columns: id a_id(foreign key to Table A) ip_address date Basically Table B contains a row for each time a user views a row from Table A. My question is how do I sort Table A results, based on the number of matching rows in Table B. i.e SELECT * FROM TableA ORDER BY (SELECT COUNT(*) FROM TableB where TableB.a_id = TableA.id) Thank you!

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• java UnitilsException: Executed scripts table "PUBLIC"."DBMAINTAIN_SCRIPTS" doesn't exist yet or is invalid [closed]

  - by Philippe

  I want use Unitils for testing my JAVA program, i have following error message "UnitilsException: Executed scripts table "PUBLIC"."DBMAINTAIN_SCRIPTS" doesn't exist yet or is invalid" My table is into an DDL file, and table is not created Could you says me if dataSetStructureGenerator.xsd.dirName=src/test/resources/dataset-schema properties is still active in unitils 3.3 ? My EMPLOYEE table is not created and DBMAINTAIN_SCRIPTS not created too Where is my mistake ? My DDL file SET REFERENTIAL_INTEGRITY FALSE; SET DATABASE COLLATION "French"; SET SCHEMA PUBLIC; CREATE TABLE DBMAINTAIN_SCRIPTS (FILE_NAME VARCHAR2(150), FILE_LAST_MODIFIED_AT INTEGER, CHECKSUM VARCHAR2(50), EXECUTED_AT VARCHAR2(20), SUCCEEDED INTEGER); CREATE TABLE EMPLOYEES(ID IDENTITY NOT NULL,NAME VARCHAR(20),TITLE VARCHAR(20),SALARY DOUBLE,NI INTEGER NOT NULL) My unitils properties file # comments documenting these unitils configuration properties removed for # brevity. look for commenting in unitils-default.properties in the root of the # unitils jar if needed. unitils.modules=database,dbunit,easymock,inject unitils.module.hibernate.enabled=false unitils.module.spring.enabled=false # these placeholders are set in avaje.properties #gere la configuration DBUNIT database.driverClassName=org.hsqldb.jdbcDriver database.url=jdbc:hsqldb:mem:unitils-example database.schemaNames=PUBLIC database.userName=SA database.password= database.dialect=hsqldb # unitils will construct the test database using the ddl file found in this # directory dbMaintainer.fileScriptSource.scripts.location=src/main/resources updateDataBaseSchema.enabled=true sequenceUpdater.sequencevalue.lowestacceptable=100 dataSetStructureGenerator.xsd.dirName=src/test/resources/dataset-schema #dbMaintainer.autoCreateExecutedScriptsTable property to true

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• Power Pivot - Average time per item

  - by Username

  I'm trying to calculate on average, how long it takes to make each item. Here is the data table: Date Item Quantity Operator 01/01/2014 Item1 3 John 01/01/2014 Item2 5 John 02/01/2014 Item1 7 Bob 02/01/2014 Item2 4 John 03/01/2014 Item1 2 Bob 07/01/2014 Item2 3 John On 01/01/2014 John made 3 of Item 1 and 5 of Item 2. If we only had the first 2 rows we can guess that it takes 0.375 days to make Item 1 and 0.625 days to make Item 2. I want to be able to calculate this on average using all the data and taking in to account the operators obviously working on different items. Thank you

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