Error Deadlock Detected Postgresql
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Psqlexception Error Deadlock Detected
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Postgres Deadlock Detected Sharelock
them; it only takes a minute: Sign up PostgreSQL : deadlock detected up vote 4 down vote favorite 1 Now, I'm using PostgresSQL for my database system and faced deadlock problem from PL/SQL function. Please find the SQL statement in postgres deadlock query the code block. (Just example) BEGIN UPDATE accounts SET balance = 0 WHERE acct_name like 'A%'; UPDATE accounts SET balance = balance + 100 WHERE acct_name like '%A'; EXCEPTION WHEN OTHERS THEN RAISE NOTICE SQLERRM; END; I've found that the deadlock occurred during this statement was running. But i'm not sure that there were other statements trying to update this table in the same time (Rather not cause I didn't found any statement which trying to update this table postgresql deadlock timeout in my logging system). So, is it possible that the deadlock was occurred within this statement ? As i know, if we blocked whole statement with BEGIN/END. There will be the same transaction and should not be locked by itself. Thanks in advance, Stoper postgresql deadlock share|improve this question edited Apr 9 '12 at 18:02 Mosty Mostacho 28.5k85689 asked Apr 9 '12 at 17:55 Sathapanic Sriprom 751414 Do you have any triggers on accounts? Also do you use explicit locking? –strkol Apr 9 '12 at 18:08 By default, a transaction can observe changes committed by other transactions. For more information, see Transaction Isolation from the PostgreSQL documentation. –Joey Adams Apr 9 '12 at 18:13 @strkol Yes I have, but statement in that trigger is not related to this table. For the explicit locking is also yes. –Sathapanic Sriprom Apr 9 '12 at 18:35 add a comment| 3 Answers 3 active oldest votes up vote 7 down vote accepted This is not a PL/SQL function. Looks like PL/pgSQL. There is definitely some other process competing for the same resource. That is the nature of a deadlock. A function like you display can never deadlock itself. See comment by @kgrittn below, who is an expert on concurrency in PostgreSQL. Your version of PostgreSQL is missing. Modern versions raise a detailed error message. Both processes that compete for resources are listed i
with deadlocks in PostgreSQL, and provides a general workflow to handle deadlock bugs and details on how to get information from PostgresSQL. If you need a gentler introduction, take a
Postgres Sharelock
look at the first article in this series. Debugging a deadlock - postgres deadlock_timeout a workflow If you have to deal with a deadlock in a complex application, usually you'll have a
Postgres Sharelock On Transaction
defect that appears in time-dependent, load-dependent and user-dependent way. It's all too easy to get lost in hypotheses! To avoid that try to work in a scientific way and follow http://stackoverflow.com/questions/10077441/postgresql-deadlock-detected a strategy. One such strategy is described below: look at Postgres logs first and try to get a rough idea of what is going on; determine what was going on at the exact time the deadlock happened. If you have a Web application, which page(s) were being loaded or submitted? If there are background jobs, were they running? If you have http://www.moioli.net/progetti/postgres-deadlocks-debugging-guidelines/ an API, were there clients using it? etc. Check all available logs as thoroughly as possible around the time the deadlock happened; if at all possible, try to trigger the problem in a reproducible way using information collected above. This might even be impossible in some cases, yet every effort should be taken to have the problem happening again predictably or you will not be able to validate any solution! based on information collected above, determine what transactions were in progress, what queries were completed before the deadlock and what queries were running at the time of the deadlock. In a big codebase this can be daunting, and ORMs such as Hibernate complicate things a lot by issuing automatically generated queries behind the scenes, yet you must, at some point, determine the active set of queries to have any chance; prototyping might help. You can, for example, attempt to write one or more test cases that exercise relevant code paths in your application and run them concurrently in order to better isolate affected components - see if you
deadlock error in my logs. It took me some time to figure out the exact situation that was causing this deadlock, and so I decided to share what I've http://elioxman.blogspot.com/2013/02/postgres-deadlock.html learned. What better way to do that than through a blog. Without further ado, let's dive in. The general setting we are talking about is Java, Spring-Data, Hibernate, Postgres, though the main issue is the Postgres https://www.postgresql.org/message-id/43132ED4.9000107@mediaroot.de DB. Let's start with the error. This would look something like that: ERROR: deadlock detected DETAIL: Process 552 waits for ExclusiveLock on tuple (0,3) of relation 16393 of database 12002; blocked by process 4924. Process 4924 deadlock detected waits for ShareLock on transaction 689; blocked by process 552. HINT: See server log for query details. Usually for me a deadlock error is a bad way to start the day. These are usually hard to reproduce, and not simple to solve. After reading a little about the different locks in Postgres and when they are used I came up with the following simple scenario which reproduces this error: Given 2 error deadlock detected tables, Parent and Child, we will try to add two children to the same parent from two different processes. After each insert we will also try to update the name of the parent. (Assume the Parent has columns: ID, Name, and the Child has columns: ID, Parent_ID, Name) Process 1: BEGIN; INSERT INTO "Child" VALUES (1, 1, 'CHILD_A'); SELECT * from pg_sleep(5); UPDATE "Parent" SET "Name"='Parent_B' WHERE "ID"=1; END; Process 2: BEGIN; INSERT INTO "Child" VALUES (2, 1, 'CHILD_B'); SELECT * from pg_sleep(5); UPDATE "Parent" SET "Name"='Parent_C' WHERE "ID"=1; END; Running these two simultaneously would result in the error above. At first it seems a little weird that this scenario gives a deadlock. I would just expect one of the processes to fail when trying to update the Parent row. The deadlock comes from the fact that when inserting a new row to the Child table, Postres acquires a RowShareLock on the Parent row (because of the foreign key). The insert from the second process also acquires a RowShareLock on the same row (acquiring two RowShareLocks is fine). When both processes come to the update statement, things become interesting. An update required a RowExclusiveLock. This lock conflicts with the RowShareLock, and so each process waits for the second one to release the Ro
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