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• ZooKeeper and RabbitMQ/Qpid together - overkill or a good combination?

  - by Chris Sears

  Greetings, I'm evaluating some components for a multi-data center distributed system. We're going to be using message queues (via either RabbitMQ or Qpid) so agents can make asynchronous requests to other agents without worrying about addressing, routing, load balancing or retransmission. In many cases, the agents will be interacting with components that were not designed for highly concurrent access, so locking and cross-agent coordination will be needed to avoid race conditions. Also, we'd like the system to automatically respond to agent or data center failures. With the above use cases in mind, ZooKeeper seemed like it might be a good fit. But I'm wondering if trying to use both ZK and message queuing is overkill. It seems like what Zookeeper does could be accomplished by my own cluster manager using AMQP messaging, but that would be hard to get really right. On the other hand, I've seen some examples where ZooKeeper was used to implement message queuing, but I think RabbitMQ/Qpid are a more natural fit for that. Has anyone out there used a combination like this? Thanks in advance, -Chris

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• Are we asking too much of transactional memory?

  - by Carl Seleborg

  I've been reading up a lot about transactional memory lately. There is a bit of hype around TM, so a lot of people are enthusiastic about it, and it does provide solutions for painful problems with locking, but you regularly also see complaints: You can't do I/O You have to write your atomic sections so they can run several times (be careful with your local variables!) Software transactional memory offers poor performance [Insert your pet peeve here] I understand these concerns: more often than not, you find articles about STMs that only run on some particular hardware that supports some really nifty atomic operation (like LL/SC), or it has to be supported by some imaginary compiler, or it requires that all accesses to memory be transactional, it introduces type constraints monad-style, etc. And above all: these are real problems. This has lead me to ask myself: what speaks against local use of transactional memory as a replacement for locks? Would this already bring enough value, or must transactional memory be used all over the place if used at all?

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• Must all Concurrent Data Store (CDB) locks be explicitly released when closing a Berkeley DB?

  - by Steve Emmerson

  I have an application that comprises multiple processes each accessing a single Berkeley DB Concurrent Data Store (CDB) database. Each process is single-threaded and does no explicit locking of the database. When each process terminates normally, it calls DB-close() and DB_ENV-close(). When all processes have terminated, there should be no locks on the database. Episodically, however, the database behaves as if some process was holding a write-lock on it even though all processes have terminated normally. Does each process need to explicitly release all locks before calling DB_ENV-close()? If so, how does the process obtain the "locker" parameter for the call to DB_ENV-loc_vec()?

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• How can two threads access a common array of buffers with minimal blocking ? (c#)

  - by Jelly Amma

  Hello, I'm working on an image processing application where I have two threads on top of my main thread: 1 - CameraThread that captures images from the webcam and writes them into a buffer 2 - ImageProcessingThread that takes the latest image from that buffer for filtering. The reason why this is multithreaded is because speed is critical and I need to have CameraThread to keep grabbing pictures and making the latest capture ready to pick up by ImageProcessingThread while it's still processing the previous image. My problem is about finding a fast and thread-safe way to access that common buffer and I've figured that, ideally, it should be a triple buffer (image[3]) so that if ImageProcessingThread is slow, then CameraThread can keep on writing on the two other images and vice versa. What sort of locking mechanism would be the most appropriate for this to be thread-safe ? I looked at the lock statement but it seems like it would make a thread block-waiting for another one to be finished and that would be against the point of triple buffering. Thanks in advance for any idea or advice. J.

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• hibernate versioning parent entity

  - by Priit

  Consider two entities Parent and Child. Child is part of Parent's transient collection Child has a ManyToOne mapping to parent with FetchType.LAZY Both are displayed on the same form to a user. When user saves the data we first update Parent instance and then Child collection (both using merge). Now comes the tricky part. When user modifies only Child property on the form then hibernate dirty checking does not update Parent instance and thus does not increase optimistic locking version number for that entity. I would like to see situation where only Parent is versioned and every time I call merge for Parent then version is always updated even if actual update is not executed in db.

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• Lock thread using somthing other than a object

  - by Scott Chamberlain

  when using a lock does the thing you are locking on have to be a object. For example is this legal static DateTime NextCleanup = DateTime.Now; const TimeSpan CleanupInterval = new TimeSpan(1, 0, 0); private static void DoCleanup() { lock ((object)NextCleanup) { if (NextCleanup < DateTime.Now) { NextCleanup = DateTime.Now.Add(CleanupInterval); System.Threading.ThreadPool.QueueUserWorkItem(new System.Threading.WaitCallback(cleanupThread)); } } return; } EDIT-- From reading SLaks' responce I know the above code would be not valid but would this be? static MyClass myClass = new MyClass(); private static void DoCleanup() { lock (myClass) { // } return; }

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• Mixing synchronized() with ReentrantLock.lock()

  - by yarvin

  In Java, do ReentrantLock.lock() and ReetrantLock.unlock() use the same locking mechanism as synchronized()? My guess is "No," but I'm hoping to be wrong. Example: Imagine that Thread 1 and Thread 2 both have access to: ReentrantLock lock = new ReentrantLock(); Thread 1 runs: synchronized (lock) { // blah } Thread 2 runs: lock.lock(); try { // blah } finally { lock.unlock(); } Assume Thread 1 reaches its part first, then Thread 2 before Thread 1 is finished: will Thread 2 wait for Thread 1 to leave the synchronized() block, or will it go ahead and run?

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• HA Proxy Stick-table and tcp-connection configuration

  - by Vladimir

  I am using HA Proxy HA-Proxy version 1.4.18 2011/09/16 I am trying to insert the following into /etc/init.d/haproxy.cfg file # Use General Purpose Couter (gpc) 0 in SC1 as a global abuse counter # Monitors the number of request sent by an IP over a period of 10 seconds stick-table type ip size 1m expire 10s store gpc0,http_req_rate(10s) tcp-request connection track-sc1 src tcp-request connection reject if { src_get_gpc0 gt 0 } # Table definition stick-table type ip size 100k expire 30s store conn_cur(3s) # Allow clean known IPs to bypass the filter tcp-request connection accept if { src -f /etc/haproxy/whitelist.lst } # Shut the new connection as long as the client has already 10 opened tcp-request connection reject if { src_conn_cur ge 10 } tcp-request connection track-sc1 src I get the following error: [ALERT] 256/113143 (4627) : parsing [/etc/haproxy/haproxy.cfg:36] : stick-table: unknown argument 'store'. [ALERT] 256/113143 (4627) : parsing [/etc/haproxy/haproxy.cfg:37] : unknown argument 'connection' after 'tcp-request' in proxy 'http_proxy' [ALERT] 256/113143 (4627) : parsing [/etc/haproxy/haproxy.cfg:38] : unknown argument 'connection' after 'tcp-request' in proxy 'http_proxy' [ALERT] 256/113143 (4627) : parsing [/etc/haproxy/haproxy.cfg:41] : stick-table: unknown argument 'store'. [ALERT] 256/113143 (4627) : parsing [/etc/haproxy/haproxy.cfg:43] : unknown argument 'connection' after 'tcp-request' in proxy 'http_proxy' [ALERT] 256/113143 (4627) : parsing [/etc/haproxy/haproxy.cfg:45] : unknown argument 'connection' after 'tcp-request' in proxy 'http_proxy' [ALERT] 256/113143 (4627) : parsing [/etc/haproxy/haproxy.cfg:46] : unknown argument 'connection' after 'tcp-request' in proxy 'http_proxy' [ALERT] 256/113143 (4627) : Error(s) found in configuration file : /etc/haproxy/haproxy.cfg [WARNING] 256/113143 (4627) : Proxy 'http_proxy': in multi-process mode, stats will be limited to process assigned to the current request. [ALERT] 256/113143 (4627) : Fatal errors found in configuration. [fail] Could you please tell me what is wrong with the code? Thanks!

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• MySQL Federated Tables Escaped Table Names

  - by Gordon

  I am trying to use MySQL federated tables. The problem is that the documentation specified at http://dev.mysql.com/doc/refman/5.0/en/federated-use.html says that a federated table should be created using the following format for the CONNECTION parameter: scheme://user_name[:password]@host_name[:port_num]/db_name/tbl_name E.G. CONNECTION='mysql://username:password@hostname:port/database/tablename' CONNECTION='mysql://username@hostname/database/tablename' CONNECTION='mysql://username:password@hostname/database/tablename' The problem is that the table I am trying to connect to has non-standard characters in it and I cannot find the proper way to scape them in the connections tring. For example, a table named `Table (one)` . Which has the space and the parenthesis, requiring backticks surrounding it inside any SQL code. Anyone know the proper way to do this?

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• Float table to bottom of page in Word 2007

  - by Christian W

  Is it possible to float a table to the bottom of a page in Word 2007? I am making a template for revisable documents for work (specs, routines etc) and I want the front page to contain the document title, and a table of revisions. I want to float this table to the bottom of the page. So as I add rows to it, it grows upwards towards the title (which is at top of page, and not middle.) Is this possible?

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• Recover mysql database - mysqldump gives "table <tablename> doesn't exist (1146)"

  - by Matthew

  Backstory Ubuntu died (wouldn't boot) and I couldn't fix it. I booted a live cd to recover the important stuff and saved it to my NAS. One of the things I backed up was /var/lib/mysql. Reinstalled with Linux Mint because I was on Ubuntu 10.0.4 this was a good opportunity to try a new distro (and I don't like Unity). Now I want to recover my old mediawiki, so I shut down mysql daemon, cp -R /media/NAS/Backup/mysql/mediawiki@002d1_19_1 /var/lib/mysql/, set file ownership and permissions correctly, and start mysql back up. Problem Now I'm trying to export the database so I can restore the database, but when I execute the mysqldump I get an error: $ mysqldump -u mediawikiuser -p mediawiki-1_19_1 -c | gzip -9 > wiki.2012-11-15.sql.gz Enter password: mysqldump: Got error: 1146: Table 'mediawiki-1_19_1.archive' doesn't exist when using LOCK TABLES Things I've tried I tried using --skip-lock-tables but I get this: Error: Couldn't read status information for table archive () mysqldump: Couldn't execute 'show create table `archive`': Table 'mediawiki-1_19_1.archive' doesn't exist (1146) I tried logging in to mysql and I can list the tables that should be there, but trying to describe or select from them errors out the same way as the dump: mysql> show tables; +----------------------------+ | Tables_in_mediawiki-1_19_1 | +----------------------------+ | archive | | category | | categorylinks | ... | user_properties | | valid_tag | | watchlist | +----------------------------+ 49 rows in set (0.00 sec) mysql> describe archive; ERROR 1146 (42S02): Table 'mediawiki-1_19_1.archive' doesn't exist I believe mediawiki was installed using innodb and binary data. Am I screwed or is there a way to recover this?

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• Running mysqlimport on a MyISAM table for hours, Data_length stays at 0

  - by Yuriy

  I'm trying to import a fairly large file (5Gb, ~130M records) into a MyISAM table (mysql 5.1.61). It's been running for more than 5 hours now with no errors displayed, and I can see "LOAD DATA INFILE ..." in the process list. However, when I run SHOW TABLE STATUS, "Data_length" for the table being updated is still 0. I wonder if that's normal - if not, I should probably abort the import to see what's wrong. "Update_time" displayed by SHOW TABLE STATUS is up-to-date and changes quickly. Is it normal for "Data_length" to remain zero while mysqlimport is successfully running?

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• Transpose matrix-style table to 3 columns in Excel

  - by polarbear2k

  I have a matrix-style table in excel where B1:Z1 are column headings and A2:A99 are row headings. I would like to convert this table to a 3 column table (column heading, row heading, cell value). It does not matter in what order the new table is. A B C D A B C A B C 1 H1 H2 H3 1 H1 R1 V1 1 H1 R1 V1 2 R1 V1 V2 V3 => 2 H1 R2 V4 or 2 H2 R1 V2 3 R2 V4 V5 V6 3 H1 R3 V7 3 H3 R1 V3 4 R3 V7 V8 V9 4 H2 R1 V2 4 H1 R2 V4 5 H2 R2 V5 5 H2 R2 V5 6 H2 R3 V8 6 H3 R2 V6 7 H3 R1 V3 7 H1 R3 V7 8 H3 R2 V6 8 H2 R3 V8 9 H3 R3 V9 9 H3 R3 V8 I've been playing around with the OFFSET function to create the whole table but I feel like a combination of TRANSPOSE and V/HLOOKUP is required. Thanks EDIT I have managed to come up with the correct formulas. If the data is in Sheet1 like in my example above, the formulas go in Sheet2: [A1] =IF(ROW() <= COUNTA(Sheet1!$B$1:$Z$1)*COUNTA(Sheet1!$A$2:$A$99), OFFSET(Sheet1!$A$1,0,IF(MOD(ROW(),COUNTA(Sheet1!$B$1:$Z$1))=0,COUNTA(Sheet1!$B$1:$Z$1),MOD(ROW(),COUNTA(Sheet1!$B$1:$Z$1)))),"") [B1] =IF(ROW() <= COUNTA(Sheet1!$B$1:$Z$1)*COUNTA(Sheet1!$A$2:$A$99),OFFSET(Sheet1!$A$1,IF(MOD(ROW(),COUNTA(Sheet1!$A$2:$A$99))=0,COUNTA(Sheet1!$A$2:$A$99),MOD(ROW(),COUNTA(Sheet1!$A$2:$A$99))),0),"") [C1] =IF(ROW() <= COUNTA(Sheet1!$B$1:$Z$1)*COUNTA(Sheet1!$A$2:$A$99),OFFSET(Sheet1!$A$1,IF(MOD(ROW(),COUNTA(Sheet1!$A$2:$A$99))=0,COUNTA(Sheet1!$A$2:$A$99),MOD(ROW(),COUNTA(Sheet1!$A$2:$A$99))),IF(MOD(ROW(),COUNTA(Sheet1!$B$1:$Z$1))=0,COUNTA(Sheet1!$B$1:$Z$1),MOD(ROW(),COUNTA(Sheet1!$B$1:$Z$1)))),"") The formulas are limited to B1:Z1 for the headings and A2:A99 for the rows (these can be increased to their maximums if required). The COUNTA() formula returns the number of cells that actually have values, which limits the number of rows returned to headings*rows. Otherwise the formulas would could go on for infinity because of the MOD function.

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• Question About mk-table-checksum Results

  - by stevenmusumeche

  Hello, I have 1 master and 2 slaves. I am using MySQL 5.1.42 on all servers. I am attempting to use mk-table-checksum to verify that their data is in sync, but I am getting unexpected results on one of the slaves. First, I generate the checksums on the master like this: mk-table-checksum h=localhost --databases MYDB --tables {$table_list} --replicate=MYDB.mk_checksum --chunk-size=10M My understanding is that this runs the checksum queries on the master which then propagate via normal replication to the slaves. So, no locking is needed because the slaves will be at the same logical point in time when they run the checksum queries on themselves. Is this correct? Next, to verify that the checksums match, I run this on the master: mk-table-checksum --databases MYDB --replicate=IRC.mk_checksum --replicate-check 1 h=localhost,u=maatkit,p=xxxx If there are any differences, I repair the slaves like this: mk-table-sync --execute --verbose --replicate IRC.mk_checksum h=localhost,u=maatkit,p=xxxx After doing all of this, I repaired both slaves with mk-table-sync. However, everytime I run this sequence (after everything has already been repaired), one slave is perfectly in sync but one slave always has a few tables out of sync. I am 99.999% sure that the data on the slaves matches, since I repaired everything and the tables were not even updated on the master between runs of the checksum script. What would cause a few tables to always show out of sync on only one of the slaves? I am stuck. Here is the output: Differences on h=x.x.x.x,p=...,u=maatkit DB TBL CHUNK CNT_DIFF CRC_DIFF BOUNDARIES IRC product 10 0 1 product_id = 147377 AND product_id < 162085 IRC post_order_survey 0 0 1 1=1 IRC mk_heartbeat 0 0 1 1=1 IRC mailing_list 0 0 1 1=1 IRC honey_pot_log 0 0 1 1=1 IRC product 12 0 1 product_id = 176793 AND product_id < 191501 IRC product 18 0 1 product_id = 265041 IRC orders 26 0 1 order_id = 694472 IRC orders_product 6 0 1 op_id = 935375

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• 'ALTER table' for all tables in a database

  - by BassKozz

  How can I run the following for every table in a database: ALTER table [table_name] type=innodb; I don't want to have to manually run it for each table, but rather run it for all tables in a database. As an aside: If your curious as to why I am running this: http://bugs.mysql.com/bug.php?id=1341 & http://bugs.mysql.com/bug.php?id=1287

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• Dynamically reference a Named Table Column via cell content in Excel

  - by rcphq

  How do I reference an Excel Table column dynamically in Excel 2007? ie: i wanna reference a named column of a named table and what table it is will vary with the value of a cell. I have a Table in Excel (Let's call it Table1). I want to reference one of its columns (Let's call it column1) dynamically from a value in another cell (A1) so that I can achieve the following result: When I change A1, the formula that counts Table1[DynamicallyReferencedColumnName] gets updated to the new reference. I tried using =Count(Table1[INDIRECT("$A$1")]) but Excel says the formula contains an error. Example: A1 = names then the formula would equal Count(Table1[names]). A1 = lastname then the formula would equal Count(Table1[lastname]).

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• A few tables are still out of sync after running mk-table-sync

  - by smusumeche

  I have 1 master and 2 slaves. I am using MySQL 5.1.42 on all servers. I am attempting to use mk-table-checksum to verify that their data is in sync, but I am getting unexpected results on one of the slaves. First, I generate the checksums on the master like this: mk-table-checksum h=localhost --databases MYDB --tables {$table_list} --replicate=MYDB.mk_checksum --chunk-size=10M My understanding is that this runs the checksum queries on the master which then propagate via normal replication to the slaves. So, no locking is needed because the slaves will be at the same logical point in time when they run the checksum queries on themselves. Is this correct? Next, to verify that the checksums match, I run this on the master: mk-table-checksum --databases MYDB --replicate=IRC.mk_checksum --replicate-check 1 h=localhost,u=maatkit,p=xxxx If there are any differences, I repair the slaves like this: mk-table-sync --execute --verbose --replicate IRC.mk_checksum h=localhost,u=maatkit,p=xxxx After doing all of this, I repaired both slaves with mk-table-sync. However, everytime I run this sequence (after everything has already been repaired), one slave is perfectly in sync but one slave always has a few tables out of sync. I am 99.999% sure that the data on the slaves matches, since I repaired everything and the tables were not even updated on the master between runs of the checksum script. What would cause a few tables to always show out of sync on only one of the slaves? I am stuck. Here is the output: Differences on h=x.x.x.x,p=...,u=maatkit DB TBL CHUNK CNT_DIFF CRC_DIFF BOUNDARIES IRC product 10 0 1 product_id = 147377 AND product_id < 162085 IRC post_order_survey 0 0 1 1=1 IRC mk_heartbeat 0 0 1 1=1 IRC mailing_list 0 0 1 1=1 IRC honey_pot_log 0 0 1 1=1 IRC product 12 0 1 product_id = 176793 AND product_id < 191501 IRC product 18 0 1 product_id = 265041 IRC orders 26 0 1 order_id = 694472 IRC orders_product 6 0 1 op_id = 935375

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• Use Excel Table Column in ComboBox Input Range property

  - by V7L

  I asked this in StackOverflow and was redirected here. Apologies for redundancy. I have an Excel worksheet with a combo box on Sheet1 that is populated via its Input Range property from a Dynamic Named Range on Sheet2. It works fine and no VBA is required. My data on Sheet2 is actually in an Excel Table (all data is in the XLS file, no external data sources). For clarity, I wanted to use a structured table reference for the combo box's Input Range, but cannot seem to find a syntax that works, e.g. myTable[[#Data],[myColumn3]] I cannot find any indications that the combo box WILL accept structured table references, though I cannot see why it wouldn't. So, two part question: 1. Is is possible to use a table column reference in the combo box input range property (not using VBA) and 2. HOW?

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• table alias (or 'symlink') in mysql

  - by andreash

  Hi there, in MySQL5.1, is there a way to make one table accessible by two different names? I'm thinking about somethink like a symlink on linux filesystems. I know theres the CREATE VIEW myview AS SELECT * FrOM mytable thing, but I don't only need to SELECT from both names, but also delete etc ... You might ask why I want to do this? It's about getting a commercial, closed-source app to work, which is crappily programmed (usually, the table names are all lower-case, but occasionally, they use capitalized names for the same table ...). Oh, that would be another idea: Is there a way to tell MySQL not to care about capitalization of table names (like on Windows filesystems?)? that would also do the trick ... Thanks for your insight! A.

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• Dropping duplicate|redundant Unique Constraint from FILESTREAM table

  - by electricsk8

  I have a table with a FILESTREAM column, and it has two unique constraints specified for the same FILESTREAM column, ie: ALTER TABLE [dbo].[TableName] ADD CONSTRAINT [UQ_TableName_33C4988760FC61CA] UNIQUE NONCLUSTERED ([GUID_Column]); GO ALTER TABLE [dbo].[TableName] ADD CONSTRAINT [UQ_TableName_33C49887145C0A3F] UNIQUE NONCLUSTERED ([GUID_Column]); GO I'd like to drop one of the unique constraints, as they are duplicates. However, when I try and drop one of the two duplicate constraints, I receive the following error. "A table with FILESTREAM column(s) must have a non-NULL unique ROWGUID column." Anyone know how to remove one of the two constraints?

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• Table 'mysql.host' doesn't exist

  - by eriktm

  100913 10:21:29 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql /usr/local/mysql/libexec/mysqld: Table 'mysql.plugin' doesn't exist 100913 10:21:29 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it. 100913 10:21:29 [ERROR] Fatal error: Can't open and lock privilege tables: Table 'mysql.host' doesn't exist 100913 10:21:29 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended This is the output from the log-file for mysqld I get when I try to start mysqld with the mysqld_safe command. I tried to run mysql_upgrade to correct the first error, but this command seems to require the server to be started, which is my original problem. Next, it says that the table mysql.host does not exist. I was unable to figure out what this is caused by.

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• Unexpected behaviour in a Lotus Notes programmable table

  - by Mark B

  I'm designing a workflow database in Lotus Notes 6.0.3 (soon upgrading to 8.5), and my OS is Windows XP. I have recently tried converting a tabbed table into a programmable one. This was so that I could control which tab was displayed to the user when it was opened, so that they were presented with the most appropriate one for that document's progress through the workflow. That part of it works! One of the tabs features a radio button that controls visibility of the next tab, and a pair of cascading dialogue boxes. One contains the static list "Person":"Team", and the other has a formula based on the first: view:=@If(PeerReview = "Team"; "GroupNames"; "GroupMembers"); @Unique(@DbColumn(""; ""; view; 1)) The dialogue boxes have the property "Refresh fields on keyword change" selected. The behaviour that I wasn't expecting is this. If the radio button is set to "Yes" and a value is selected in one of the dialogue boxes, the table opens the next tab. If the radio button is set to "No" and a value is selected in one of the dialogue boxes, the entire table is hidden. I can duplicate the latter by switching off the "Refresh fields on keyword change" property on the dialogue boxes and instead pressing F9 after selecting a value. I have no idea why the former occurs, though. The table is called "RFCInfo", and I have a field on the form called "$RFCInfo" which is editable, hidden from all users who aren't me and initially set by a Postopen script, which I can post if necessary - it's essentially a Select Case statement that looks at a particular item value and returns the name of the table row relating to that value. Can anyone offer any pointers?

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• Open table cache in MySQL

  - by vvanscherpenseel

  I have my open table cache set to 1800 and I have a total of 1112 tables. MySQL Tuning Primer reports that 100% of my table cache is used yet my table cache hit rate is 5%. I understand that this happens due to concurrent connections all opening tables. I think I should raise the cache limit. I understand that the cache size is limited by the file descriptor limit of my operating system, but are there any other practical limitations I should be aware of? Searching Google or this very website yields mostly posts explaining the connection-factor or come up with indecisive answers. My question: can I safely increase the open table cache limit? Is there a maximum?

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• Deleting Duplicates in MySQL

  - by elmaso

  Query was this: CREATE TABLE `query` ( `id` int(11) NOT NULL auto_increment, `searchquery` varchar(255) NOT NULL default '', `datetime` int(11) NOT NULL default '0', PRIMARY KEY (`id`) ) ENGINE=MyISAM first I want to drop the table with: ALTER TABLE `querynew` DROP `id` and then delete the double entries.. I tried it with: INSERT INTO `querynew` SELECT DISTINCT * FROM `query` but with no success.. :( and with ALTER TABLE query ADD UNIQUE ( searchquery ) - is it possible to save the queries only one time?

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• SQL Server CTE referred in self joins slow

  - by Kharlos Dominguez

  Hello, I have written a table-valued UDF that starts by a CTE to return a subset of the rows from a large table. There are several joins in the CTE. A couple of inner and one left join to other tables, which don't contain a lot of rows. The CTE has a where clause that returns the rows within a date range, in order to return only the rows needed. I'm then referencing this CTE in 4 self left joins, in order to build subtotals using different criterias. The query is quite complex but here is a simplified pseudo-version of it WITH DataCTE as ( SELECT [columns] FROM table INNER JOIN table2 ON [...] INNER JOIN table3 ON [...] LEFT JOIN table3 ON [...] ) SELECT [aggregates_columns of each subset] FROM DataCTE Main LEFT JOIN DataCTE BananasSubset ON [...] AND Product = 'Bananas' AND Quality = 100 LEFT JOIN DataCTE DamagedBananasSubset ON [...] AND Product = 'Bananas' AND Quality < 20 LEFT JOIN DataCTE MangosSubset ON [...] GROUP BY [ I have the feeling that SQL Server gets confused and calls the CTE for each self join, which seems confirmed by looking at the execution plan, although I confess not being an expert at reading those. I would have assumed SQL Server to be smart enough to only perform the data retrieval from the CTE only once, rather than do it several times. I have tried the same approach but rather than using a CTE to get the subset of the data, I used the same select query as in the CTE, but made it output to a temp table instead. The version referring the CTE version takes 40 seconds. The version referring the temp table takes between 1 and 2 seconds. Why isn't SQL Server smart enough to keep the CTE results in memory? I like CTEs, especially in this case as my UDF is a table-valued one, so it allowed me to keep everything in a single statement. To use a temp table, I would need to write a multi-statement table valued UDF, which I find a slightly less elegant solution. Did some of you had this kind of performance issues with CTE, and if so, how did you get them sorted? Thanks, Kharlos

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