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• Explain JAVA code

  - by MIW

  I need some help to explain the meaning from line 5 to line 9. Thanks String words = "Rain Rain go away"; String mutation1, mutation2, mutation3, mutation4; mutation1 = words.toUpperCase(); System.out.println ("** " + mutation1 + " Nursery Rhyme **"); mutation1 = words.concat ("\nCome again another day"); mutation2 = "Johnny Johnny wants to play"; mutation3 = mutation2.replace (mutation2.charAt(5), 'i'); mutation4 = mutation3.substring (7, 27); System.out.print ("\'" + mutation1 + "\n" + mutation4 + "\'\n"); 10.System.out.println ("Title length: " + words.length());

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• Explain a block of crazy JS code inside Sizzle(the CSS selector engine)

  - by Andy Li

  So, here is the function for pre-filtering "CHILD": function(match){ if ( match[1] === "nth" ) { // parse equations like 'even', 'odd', '5', '2n', '3n+2', '4n-1', '-n+6' var test = /(-?)(\d*)n((?:\+|-)?\d*)/.exec( match[2] === "even" && "2n" || match[2] === "odd" && "2n+1" || !/\D/.test( match[2] ) && "0n+" + match[2] || match[2]); // calculate the numbers (first)n+(last) including if they are negative match[2] = (test[1] + (test[2] || 1)) - 0; match[3] = test[3] - 0; } // TODO: Move to normal caching system match[0] = done++; return match; } The code is extracted from line 442-458 of sizzle.js. So, why is the line var test = ..., have the exec inputing a boolean? Or is that really a string? Can someone explain it by splitting it into a few more lines of code?

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• Can anyone explain this snippet of Javascript?

  - by karthick6891

  Can anyone explain the following code? Forget the sine and cosine parts. Is it trying to build a space for the object? objectsInScene = new Array(); for (var i=space; i<180; i+=space) { for (var angle=0; angle<360; angle+=space) { var object = {}; var x = Math.sin(radian*i)*radius; object.x = Math.cos(angle*radian)*x; object.y = Math.cos(radian*i)*radius; object.z = Math.sin(angle*radian)*x; objectsInScene.push(object); } }

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• Explain DLL Dependencies to a lay person

  - by wheaties

  This follows from a previous posting I made about lack of a clean test machine for software installations. I'm doing a bad job of explaining how DLL dependencies work and how some machines might not have the right libraries at the time of installation. The problem is that it's being viewed as a defect with the build process. I'm trying to educate the higher ups that it's not the build process per se but rather the installation process which is to blame. Here's a quote from my boss relating subcontractor work to our work to put it into perspective: I'm not a software person. All I see is that when they hand something to us it just works but when we hand something to the client there's all sorts of problems. There must be something wrong with how you're building the code. It's very easy to see how someone who is smart (scarily smart) could come to the wrong conclusion. So how would you explain the whole DLL dependency issue?

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• Can anyone explain this pience of snippet?

  - by karthick6891

  Can anyone explain the following code,forget the sin and cosine parts..Is it trying to build a space for the object objectsInScene = new Array(); for (var i=space; i<180; i+=space) { for (var angle=0; angle<360; angle+=space) { var object = {}; var x = Math.sin(radian*i)*radius; object.x = Math.cos(angle*radian)*x; object.y = Math.cos(radian*i)*radius; object.z = Math.sin(angle*radian)*x; objectsInScene.push(object); } }

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• Explain this O(n log n) algorithm for the Cat/Egg Throwing Problem

  - by ripper234

  This problem (How many cats you need to throw out of a building in order to determine the maximal floor where such a cat will survive. Quite cruel, actually), has an accepted answer with O(n^3) complexity. The problem is equivalent to this Google Code Jam, which should be solvable for N=2000000000. It seems that the O(n^3) solution is not good enough to solve it. From looking in the solutions page, jdmetz's solution (#2) seems to be O(n log n). I don't quite understand the algorithm. Can someone explain it? Edit

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• can anyone explain the why the the 1st example gets different results than the following 2

  - by klumsy

  $b = (2,3) $myarray1 = @(,$b,$b) $myarray1[0].length #this will be 1 $myarray1[1].length $myarray2 = @( ,$b ,$b ) $myarray2[0].length #this will be 2 $myarray[1].length $myarray3 = @(,$b ,$b ) $myarray3[0].length #this will be 2 $myarray3[1].length UPDATE I think on #powershell IRC we have worked it out, Here is another example that demonstrates the danger of breaking with the comma on the following line rather than the top line when listing multiple items in an array over multiple lines. $b = (1..20) $a = @( $b, $b ,$b, $b, $b ,$b) for($i=0;$i -lt $a.length;$i++) { $a[$i].length } "--------" $a = @( $b, $b ,$b ,$b, $b ,$b) for($i=0;$i -lt $a.length;$i++) { $a[$i].length } produces 20 20 20 20 20 20 -------- 20 20 20 1 20 20 I'm curious how people will explain this. I think i understand it now, but would have trouble explaining it in a concise understandable fashion, though the above example goes somewhat towards that goal.

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• please explain the dataflow in MVC specially in codeigniter

  - by pokhara

  Dear friends, Can anyone please explain me the object flow in codeigniter MVC ? I can see for example when I put the followong code in controller it works, but i am not being able to figure out which part of this goes in model in vews. I tried several ways but coudn't. When i use the example codes from other it works but myself i am getting confused. Please help $query = $this->db->query("YOUR QUERY"); foreach ($query->result() as $row) { echo $row->title; echo $row->name; echo $row->body; }

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• Can someone explain Kohana 3's routing system?

  - by alex

  In bootstrap.php, where you set routes, I'm having a hard time getting them to work. I read some documentation a while ago that I can't seem to find again that explains them. Here is one of my examples Route::set('products', 'products/(type)', array('type' => '.+')) ->defaults(array( 'controller' => 'articles', 'action' => 'view_product', 'page' => 'shock-absorbers', )); I thought that would mean a request like products/something would load up the articles controller, and the action_view_product method. But I can't get it to work. Can someone please explain to me exactly how they work, and what all the method parameters are?

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• Help me to explain the F# Matrix transpose function

  - by Kev

  There is a Matrix transpose function: let rec transpose = function | (_::_)::_ as M -> List.map List.head M :: transpose (List.map List.tail M) | _ -> [] [[1; 2; 3]; [4; 5; 6]; [7; 8; 9]] |> transpose |> printfn "%A" It works fine. What does ( _ :: _ ) :: _ mean? I don't understand the whole code! Who can explain it? Thank You!

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• Can anybody explain the working of following code...?

  - by Siddhi

  Can anybody explain the working of following code...? interface myInterface{} public class Main { public static void main(String[] args) { System.out.println(new myInterface(){public String toString(){return "myInterfacetoString";}}); System.out.println(new myInterface(){public String myFunction(){return "myInterfacemyFunction";}}); } } Output is... myInterfacetoString primitivedemo.Main$2@9304b1 All answers saying that myInterface in println() statement is anonymous class. But as I already declared it as an interface, why does it allow me to create anonymous class of same name....? again...if these are anonymous classes then class main should allow me to give any name to these anonymous classes..But if try to do so..I'm getting compilation error

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• MySQL query optimization - distinct, order by and limit

  - by Manuel Darveau

  I am trying to optimize the following query: select distinct this_.id as y0_ from Rental this_ left outer join RentalRequest rentalrequ1_ on this_.id=rentalrequ1_.rental_id left outer join RentalSegment rentalsegm2_ on rentalrequ1_.id=rentalsegm2_.rentalRequest_id where this_.DTYPE='B' and this_.id<=1848978 and this_.billingStatus=1 and rentalsegm2_.endDate between 1273631699529 and 1274927699529 order by rentalsegm2_.id asc limit 0, 100; This query is done multiple time in a row for paginated processing of records (with a different limit each time). It returns the ids I need in the processing. My problem is that this query take more than 3 seconds. I have about 2 million rows in each of the three tables. Explain gives: +----+-------------+--------------+--------+-----------------------------------------------------+---------------+---------+--------------------------------------------+--------+----------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+--------------+--------+-----------------------------------------------------+---------------+---------+--------------------------------------------+--------+----------------------------------------------+ | 1 | SIMPLE | rentalsegm2_ | range | index_endDate,fk_rentalRequest_id_BikeRentalSegment | index_endDate | 9 | NULL | 449904 | Using where; Using temporary; Using filesort | | 1 | SIMPLE | rentalrequ1_ | eq_ref | PRIMARY,fk_rental_id_BikeRentalRequest | PRIMARY | 8 | solscsm_main.rentalsegm2_.rentalRequest_id | 1 | Using where | | 1 | SIMPLE | this_ | eq_ref | PRIMARY,index_billingStatus | PRIMARY | 8 | solscsm_main.rentalrequ1_.rental_id | 1 | Using where | +----+-------------+--------------+--------+-----------------------------------------------------+---------------+---------+--------------------------------------------+--------+----------------------------------------------+ I tried to remove the distinct and the query ran three times faster. explain without the query gives: +----+-------------+--------------+--------+-----------------------------------------------------+---------------+---------+--------------------------------------------+--------+-----------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+--------------+--------+-----------------------------------------------------+---------------+---------+--------------------------------------------+--------+-----------------------------+ | 1 | SIMPLE | rentalsegm2_ | range | index_endDate,fk_rentalRequest_id_BikeRentalSegment | index_endDate | 9 | NULL | 451972 | Using where; Using filesort | | 1 | SIMPLE | rentalrequ1_ | eq_ref | PRIMARY,fk_rental_id_BikeRentalRequest | PRIMARY | 8 | solscsm_main.rentalsegm2_.rentalRequest_id | 1 | Using where | | 1 | SIMPLE | this_ | eq_ref | PRIMARY,index_billingStatus | PRIMARY | 8 | solscsm_main.rentalrequ1_.rental_id | 1 | Using where | +----+-------------+--------------+--------+-----------------------------------------------------+---------------+---------+--------------------------------------------+--------+-----------------------------+ As you can see, the Using temporary is added when using distinct. I already have an index on all fields used in the where clause. Is there anything I can do to optimize this query? Thank you very much!

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• Please explain this delete top 100 SQL syntax

  - by Patrick

  Basically I want to do this: delete top( 100 ) from table order by id asc but MS SQL doesn't allow order in this position The common solution seems to be this: DELETE table WHERE id IN(SELECT TOP (100) id FROM table ORDER BY id asc) But I also found this method here: delete table from (select top (100) * from table order by id asc) table which has a much better estimated execution plan (74:26). Unfortunately I don't really understand the syntax, please can some one explain it to me? Always interested in any other methods to achieve the same result as well. EDIT: I'm still not getting it I'm afraid, I want to be able to read the query as I read the first two which are practically English. The above queries to me are: delete the top 100 records from table, with the records ordered by id ascending delete the top 100 records from table where id is anyone of (this lot of ids) delete table from (this lot of records) table I can't change the third one into a logical English sentence... I guess what I'm trying to get at is how does this turn into "delete from table (this lot of records)". The 'from' seems to be in an illogical position and the second mention of 'table' is logically superfluous (to me).

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• oracle using index even though there is no filter criteeria specified

  - by Kaushik

  In this query: SELECT WTTEMPLATE.TEMPLATEuID, MAX (WTTRX.VALUEDATE) AS template_last_use_date FROM wttemplate, wttrx WHERE WTTEMPLATE.TEMPLATEID = WTTRX.TEMPLATEID(+) AND WTTEMPLATE.CUSTID = WTTRX.CUSTID GROUP BY WTTEMPLATE.TEMPLATEuID The explain plan shows:index fast full scan using indexes on WTTEMPLATE.TEMPLATEID and (WTTRX.TEMPLATEID,WTTRX.CUSTID). My question is this: I have not specified any filter criteria , so how can it use indexes? It should do full scan...right?

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• Building a maven child project that depends on another projects child project with Bamboo

  - by kosoant

  I have two maven projects Project AAA * AAA-Core * AAA-Other Project BBB * BBB-Core * BBB-AAA-specific I want to create a build plan in Bamboo to build the BBB-AAA-specific project. The plan configuration is such that this project depends on the AAA-Other projec build. Thus everything should work ok. But when I try to run the BBB-AAA-specific Bamboo plan I get an error that states: "Unable to find resource 'foo.bar.AAA:AAA:pom:0.0.1-SNAPSHOT' in repository snapshots (http://foo.bar.com)" What is going on? The bamboo builds for "AAA-Core" and "AAA-Other" work as expected.

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• Can you make a SQL Server Maintenance Subplan run after a previous subplan completes

  - by Adam J.R. Erickson

  I have a maintenance plan to do backups and cleanup of old data. It has three subplans, each with their own schedule. Can I set the schedule of subtask 2 to be "after subtask 1 is complete"?

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• Can someone please explain this lazy evaluation code?

  - by Tejs

  So, this question was just asked on SO: http://stackoverflow.com/questions/2740001/how-to-handle-an-infinite-ienumerable My sample code: public static void Main(string[] args) { foreach (var item in Numbers().Take(10)) Console.WriteLine(item); Console.ReadKey(); } public static IEnumerable<int> Numbers() { int x = 0; while (true) yield return x++; } Can someone please explain why this is lazy evaluated? I've looked up this code in Reflector, and I'm more confused than when I began. Reflector outputs: public static IEnumerable<int> Numbers() { return new <Numbers>d__0(-2); } For the numbers method, and looks to have generated a new type for that expression: [DebuggerHidden] public <Numbers>d__0(int <>1__state) { this.<>1__state = <>1__state; this.<>l__initialThreadId = Thread.CurrentThread.ManagedThreadId; } This makes no sense to me. I would have assumed it was an infinite loop until I put that code together and executed it myself.

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• Image Line Trace Math Help Hard To Explain

  - by Ozzy

  Hi all, sorry for the confusing title, its really hard for me to explain what i want. So i created this image :) Ok so the two RED dots are points on an image. The distance between them isnt important. What I want to do is, Using the coordinates for the two dots, work out the angle of the space between them (as shown by the black line between the red dots) Then once the angle is found, on the last red dot, create two points which cross the angle of the first line. Then from that, scan a Half semicircle and get the coordinates of every pixel of the image that the orange line passes. I dnot know if this makes any sense to you lot so i drew another picture: As you can see in the second picture, my idea is applied to a line drawn on a black canavs. The two red dots are the starting coordinates then at the end of the two dots, a less then half semicircle is created. The part that is orange shows the pixels of the image that should be recorded. I have no clue how to start this, so if anyone has any ideas on how i can or on what i need to do, any help is much appreciated :)

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• Can someone explain me this code ?

  - by VaioIsBorn

  #include <stdio.h> #include <unistd.h> #include <string.h> int good(int addr) { printf("Address of hmm: %p\n", addr); } int hmm() { printf("Win.\n"); execl("/bin/sh", "sh", NULL); } extern char **environ; int main(int argc, char **argv) { int i, limit; for(i = 0; environ[i] != NULL; i++) memset(environ[i], 0x00, strlen(environ[i])); int (*fptr)(int) = good; char buf[32]; if(strlen(argv[1]) <= 40) limit = strlen(argv[1]); for(i = 0; i <= limit; i++) { buf[i] = argv[1][i]; if(i < 36) buf[i] = 0x41; } int (*hmmptr)(int) = hmm; (*fptr)((int)hmmptr); return 0; } I don't really understand the code above, i have it from an online game - i should supply something in the arguments so it would give me shell, but i don't get it how it works so i don't know what to do. So i need someone that would explain it what it does, how it's working and the stuff. Thanks.

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• Can somebody explain this remark in the MSDN CreateMutex() documentation about the bInitialOwner fla

  - by Tom Williams

  The MSDN CreatMutex() documentation (http://msdn.microsoft.com/en-us/library/ms682411%28VS.85%29.aspx) contains the following remark near the end: Two or more processes can call CreateMutex to create the same named mutex. The first process actually creates the mutex, and subsequent processes with sufficient access rights simply open a handle to the existing mutex. This enables multiple processes to get handles of the same mutex, while relieving the user of the responsibility of ensuring that the creating process is started first. When using this technique, you should set the bInitialOwner flag to FALSE; otherwise, it can be difficult to be certain which process has initial ownership. Can somebody explain the problem with using bInitialOwner = TRUE? Earlier in the same documentation it suggests a call to GetLastError() will allow you to determine whether a call to CreateMutext() created the mutex or just returned a new handle to an existing mutex: Return Value If the function succeeds, the return value is a handle to the newly created mutex object. If the function fails, the return value is NULL. To get extended error information, call GetLastError. If the mutex is a named mutex and the object existed before this function call, the return value is a handle to the existing object, GetLastError returns ERROR_ALREADY_EXISTS, bInitialOwner is ignored, and the calling thread is not granted ownership. However, if the caller has limited access rights, the function will fail with ERROR_ACCESS_DENIED and the caller should use the OpenMutex function.

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• Can someone please explain Cursor in android ?

  - by Prabhat

  Can some one explain how the cursor exactly works ? Or the flow of the following part of the code ? I know that this is sub activity and all but I did not understand how Cursor works exactly. final Uri data = Uri.parse("content://contacts/people/"); final Cursor c = managedQuery(data, null, null, null, null); String[] from = new String[] { People.NAME }; int[] to = new int[] { R.id.itemTextView }; SimpleCursorAdapter adapter = new SimpleCursorAdapter(this,R.layout.listitemlayout, c, from, to); ListView lv = (ListView) findViewById(R.id.contactListView); lv.setAdapter(adapter); lv.setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View view, int pos, long id) { c.moveToPosition(pos); int rowId = c.getInt(c.getColumnIndexOrThrow("_id")); Uri outURI = Uri.parse(data.toString() + rowId); Intent outData = new Intent(); outData.setData(outURI); setResult(Activity.RESULT_OK, outData); finish(); } }); Thanks.

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• How to explain to client that you can't give them some of the source

  - by Bo

  We have a number of AS/Flex components that we've built over time and improved upon. They've been turned into components so they can be reused in different projects and save us time. So you can think of them as part of an in-house framework of sorts. We're now realizing that it doesn't make sense to release the source code for these components to the various clients as part of the project, because technically this code isn't really owned by the clients. So my question When a client comes to you, how do you explain to them that you can't give them the full source code for those components. The client doesn't understand the difference, he just expects you to give them all the code for the site that he paid you to do. He doesn't understand that this code has taken you a lot longer to write than what he's paying for his site. But since he doesn't understand, he would get turned off and thinks you're ripping him off or something. How do you handle this situation? What do you tell clients upfront? Do you advertise it on your site from the very beginning? How do you handle their objections so they still hire you? As a side question, how often do you give AS and Flex source code to your clients? In the case when the code doesn't have any in-house components that you reuse in several projects, and in the case when it does have in-house components.

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• explain notifier.c from the Linux kernel

  - by apollon

  I'm seeking to fully understand the following code snippet from kernel/notifier.c. I have read and built simple link lists and think I get the construct from K&R's C programming. The second line below which begins with the 'int' appears to be two items together which is unclear. The first is the (*notifier_call) which I believe has independent but related significance with the second containing a 'notifier block' term. Can you explain how it works in detail? I understand that there is a function pointer and multiple subscribers possible. But I lack the way to tie these facts together, and could use a primer or key so I exactly understand how the code works. The third line looks to contain the linking structure, or recursive nature. Forgive my terms, and correct them as fit as I am a new student of computer science terminology. struct notifier_block { int (*notifier_call)(struct notifier_block *, unsigned long, void *); struct notifier_block *next; int priority; };

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• MySQL Query performance - huge difference in time

  - by Damo

  I have a query that is returning in vastly different amounts of time between 2 datasets. For one set (database A) it returns in a few seconds, for the other (database B)....well I haven't waited long enough yet, but over 10 minutes. I have dumped both of these databases to my local machine where I can reproduce the issue running MySQL 5.1.37. Curiously, database B is smaller than database A. A stripped down version of the query that reproduces the problem is: SELECT * FROM po_shipment ps JOIN po_shipment_item psi USING (ship_id) JOIN po_alloc pa ON ps.ship_id = pa.ship_id AND pa.UID_items = psi.UID_items JOIN po_header ph ON pa.hdr_id = ph.hdr_id LEFT JOIN EVENT_TABLE ev0 ON ev0.TABLE_ID1 = ps.ship_id AND ev0.EVENT_TYPE = 'MAS0' LEFT JOIN EVENT_TABLE ev1 ON ev1.TABLE_ID1 = ps.ship_id AND ev1.EVENT_TYPE = 'MAS1' LEFT JOIN EVENT_TABLE ev2 ON ev2.TABLE_ID1 = ps.ship_id AND ev2.EVENT_TYPE = 'MAS2' LEFT JOIN EVENT_TABLE ev3 ON ev3.TABLE_ID1 = ps.ship_id AND ev3.EVENT_TYPE = 'MAS3' LEFT JOIN EVENT_TABLE ev4 ON ev4.TABLE_ID1 = ps.ship_id AND ev4.EVENT_TYPE = 'MAS4' LEFT JOIN EVENT_TABLE ev5 ON ev5.TABLE_ID1 = ps.ship_id AND ev5.EVENT_TYPE = 'MAS5' WHERE ps.eta >= '2010-03-22' GROUP BY ps.ship_id LIMIT 100; The EXPLAIN query plan for the first database (A) that returns in ~2 seconds is: +----+-------------+-------+--------+----------------------------------------------------------------------------------------------------------------------------------------+----------------------------------+---------+------------------------------+------+----------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+--------+----------------------------------------------------------------------------------------------------------------------------------------+----------------------------------+---------+------------------------------+------+----------------------------------------------+ | 1 | SIMPLE | ps | range | PRIMARY,IX_ETA_DATE | IX_ETA_DATE | 4 | NULL | 174 | Using where; Using temporary; Using filesort | | 1 | SIMPLE | ev0 | ref | IX_EVENT_ID_EVENT_TYPE | IX_EVENT_ID_EVENT_TYPE | 36 | UNIVIS_PROD.ps.ship_id,const | 1 | | | 1 | SIMPLE | ev1 | ref | IX_EVENT_ID_EVENT_TYPE | IX_EVENT_ID_EVENT_TYPE | 36 | UNIVIS_PROD.ps.ship_id,const | 1 | | | 1 | SIMPLE | ev2 | ref | IX_EVENT_ID_EVENT_TYPE | IX_EVENT_ID_EVENT_TYPE | 36 | UNIVIS_PROD.ps.ship_id,const | 1 | | | 1 | SIMPLE | ev3 | ref | IX_EVENT_ID_EVENT_TYPE | IX_EVENT_ID_EVENT_TYPE | 36 | UNIVIS_PROD.ps.ship_id,const | 1 | | | 1 | SIMPLE | ev4 | ref | IX_EVENT_ID_EVENT_TYPE | IX_EVENT_ID_EVENT_TYPE | 36 | UNIVIS_PROD.ps.ship_id,const | 1 | | | 1 | SIMPLE | ev5 | ref | IX_EVENT_ID_EVENT_TYPE | IX_EVENT_ID_EVENT_TYPE | 36 | UNIVIS_PROD.ps.ship_id,const | 1 | | | 1 | SIMPLE | psi | ref | PRIMARY,IX_po_shipment_item_po_shipment1,FK_po_shipment_item_po_shipment1 | IX_po_shipment_item_po_shipment1 | 4 | UNIVIS_PROD.ps.ship_id | 1 | | | 1 | SIMPLE | pa | ref | IX_po_alloc_po_shipment_item2,IX_po_alloc_po_details_old,FK_po_alloc_po_shipment1,FK_po_alloc_po_shipment_item1,FK_po_alloc_po_header1 | FK_po_alloc_po_shipment1 | 4 | UNIVIS_PROD.psi.ship_id | 5 | Using where | | 1 | SIMPLE | ph | eq_ref | PRIMARY,IX_HDR_ID | PRIMARY | 4 | UNIVIS_PROD.pa.hdr_id | 1 | | +----+-------------+-------+--------+----------------------------------------------------------------------------------------------------------------------------------------+----------------------------------+---------+------------------------------+------+----------------------------------------------+ The EXPLAIN query plan for the second database (B) that returns in 600 seconds is: +----+-------------+-------+--------+----------------------------------------------------------------------------------------------------------------------------------------+----------------------------------+---------+--------------------------------+------+----------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+--------+----------------------------------------------------------------------------------------------------------------------------------------+----------------------------------+---------+--------------------------------+------+----------------------------------------------+ | 1 | SIMPLE | ps | range | PRIMARY,IX_ETA_DATE | IX_ETA_DATE | 4 | NULL | 38 | Using where; Using temporary; Using filesort | | 1 | SIMPLE | psi | ref | PRIMARY,IX_po_shipment_item_po_shipment1,FK_po_shipment_item_po_shipment1 | IX_po_shipment_item_po_shipment1 | 4 | UNIVIS_DEV01.ps.ship_id | 1 | | | 1 | SIMPLE | ev0 | ref | IX_EVENT_ID_EVENT_TYPE | IX_EVENT_ID_EVENT_TYPE | 36 | UNIVIS_DEV01.psi.ship_id,const | 1 | | | 1 | SIMPLE | ev1 | ref | IX_EVENT_ID_EVENT_TYPE | IX_EVENT_ID_EVENT_TYPE | 36 | UNIVIS_DEV01.psi.ship_id,const | 1 | | | 1 | SIMPLE | ev2 | ref | IX_EVENT_ID_EVENT_TYPE | IX_EVENT_ID_EVENT_TYPE | 36 | UNIVIS_DEV01.ps.ship_id,const | 1 | | | 1 | SIMPLE | ev3 | ref | IX_EVENT_ID_EVENT_TYPE | IX_EVENT_ID_EVENT_TYPE | 36 | UNIVIS_DEV01.psi.ship_id,const | 1 | | | 1 | SIMPLE | ev4 | ref | IX_EVENT_ID_EVENT_TYPE | IX_EVENT_ID_EVENT_TYPE | 36 | UNIVIS_DEV01.psi.ship_id,const | 1 | | | 1 | SIMPLE | ev5 | ref | IX_EVENT_ID_EVENT_TYPE | IX_EVENT_ID_EVENT_TYPE | 36 | UNIVIS_DEV01.ps.ship_id,const | 1 | | | 1 | SIMPLE | pa | ref | IX_po_alloc_po_shipment_item2,IX_po_alloc_po_details_old,FK_po_alloc_po_shipment1,FK_po_alloc_po_shipment_item1,FK_po_alloc_po_header1 | IX_po_alloc_po_shipment_item2 | 4 | UNIVIS_DEV01.ps.ship_id | 4 | Using where | | 1 | SIMPLE | ph | eq_ref | PRIMARY,IX_HDR_ID | PRIMARY | 4 | UNIVIS_DEV01.pa.hdr_id | 1 | | +----+-------------+-------+--------+----------------------------------------------------------------------------------------------------------------------------------------+----------------------------------+---------+--------------------------------+------+----------------------------------------------+ When database B is running I can look at the MySQL Administrator and the state remains at "Copying to tmp table" indefinitely. Database A also has this state but for only a second or so. There are no differences in the table structure, indexes, keys etc between these databases (I have done show create tables and diff'd them). The sizes of the tables are: database A: po_shipment 1776 po_shipment_item 1945 po_alloc 36298 po_header 71642 EVENT_TABLE 1608 database B: po_shipment 463 po_shipment_item 470 po_alloc 3291 po_header 56149 EVENT_TABLE 1089 Some points to note: Removing the WHERE clause makes the query return < 1 sec. Removing the GROUP BY makes the query return < 1 sec. Removing ev5, ev4, ev3 etc makes the query get faster for each one removed. Can anyone suggest how to resolve this issue? What have I missed? Many Thanks.

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• Is there a way to delay compilation of a stored procedure's execution plan?

  - by Ian Henry

  (At first glance this may look like a duplicate of http://stackoverflow.com/questions/421275 or http://stackoverflow.com/questions/414336, but my actual question is a bit different) Alright, this one's had me stumped for a few hours. My example here is ridiculously abstracted, so I doubt it will be possible to recreate locally, but it provides context for my question (Also, I'm running SQL Server 2005). I have a stored procedure with basically two steps, constructing a temp table, populating it with very few rows, and then querying a very large table joining against that temp table. It has multiple parameters, but the most relevant is a datetime "@MinDate." Essentially: create table #smallTable (ID int) insert into #smallTable select (a very small number of rows from some other table) select * from aGiantTable inner join #smallTable on #smallTable.ID = aGiantTable.ID inner join anotherTable on anotherTable.GiantID = aGiantTable.ID where aGiantTable.SomeDateField > @MinDate If I just execute this as a normal query, by declaring @MinDate as a local variable and running that, it produces an optimal execution plan that executes very quickly (first joins on #smallTable and then only considers a very small subset of rows from aGiantTable while doing other operations). It seems to realize that #smallTable is tiny, so it would be efficient to start with it. This is good. However, if I make that a stored procedure with @MinDate as a parameter, it produces a completely inefficient execution plan. (I am recompiling it each time, so it's not a bad cached plan...at least, I sure hope it's not) But here's where it gets weird. If I change the proc to the following: declare @LocalMinDate datetime set @LocalMinDate = @MinDate --where @MinDate is still a parameter create table #smallTable (ID int) insert into #smallTable select (a very small number of rows from some other table) select * from aGiantTable inner join #smallTable on #smallTable.ID = aGiantTable.ID inner join anotherTable on anotherTable.GiantID = aGiantTable.ID where aGiantTable.SomeDateField > @LocalMinDate Then it gives me the efficient plan! So my theory is this: when executing as a plain query (not as a stored procedure), it waits to construct the execution plan for the expensive query until the last minute, so the query optimizer knows that #smallTable is small and uses that information to give the efficient plan. But when executing as a stored procedure, it creates the entire execution plan at once, thus it can't use this bit of information to optimize the plan. But why does using the locally declared variables change this? Why does that delay the creation of the execution plan? Is that actually what's happening? If so, is there a way to force delayed compilation (if that indeed is what's going on here) even when not using local variables in this way? More generally, does anyone have sources on when the execution plan is created for each step of a stored procedure? Googling hasn't provided any helpful information, but I don't think I'm looking for the right thing. Or is my theory just completely unfounded? Edit: Since posting, I've learned of parameter sniffing, and I assume this is what's causing the execution plan to compile prematurely (unless stored procedures indeed compile all at once), so my question remains -- can you force the delay? Or disable the sniffing entirely? The question is academic, since I can force a more efficient plan by replacing the select * from aGiantTable with select * from (select * from aGiantTable where ID in (select ID from #smallTable)) as aGiantTable Or just sucking it up and masking the parameters, but still, this inconsistency has me pretty curious.

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