The deadlock can happen if your statement successfully locks a couple of rows and then blocks on a lock on some other row. In that case, you may end up with a FOR KEY SHARE lock on the referenced table. The updated table has a foreign key constraint to another table. Note: While this query will mostly work fine, it still has some correctness issues, particularly on 9.6. The query modifies more than a single row in the target table. pg_stat_activity blocking_activity ON blocking_activity. objsubid IS NOT DISTINCT FROM blocked_locks. objid IS NOT DISTINCT FROM blocked_locks. classid IS NOT DISTINCT FROM blocked_locks. ![]() maxpredlocksperpage (integer) This controls how many rows on a single page can be predicate-locked before the lock is promoted to covering the whole page. This parameter can only be set in the nf file or on the server command line. transactionid IS NOT DISTINCT FROM blocked_locks. The default is -2, which keeps the behavior from previous versions of PostgreSQL. virtualxid IS NOT DISTINCT FROM blocked_locks. tuple IS NOT DISTINCT FROM blocked_locks. relation IS NOT DISTINCT FROM blocked_locks. DATABASE IS NOT DISTINCT FROM blocked_locks. pg_locks blocking_locks ON blocking_locks. pg_stat_activity blocked_activity ON blocked_activity. application_name AS blocking_application FROM pg_catalog. application_name AS blocked_application, blocking_activity. query AS current_statement_in_blocking_process, blocked_activity. Browse other questions tagged postgresql concurrency deadlock database-deadlocks or ask your own question. query AS blocked_statement, blocking_activity. usename AS blocking_user, blocked_activity. usename AS blocked_user, blocking_locks. It can be information which source code line starts transaction or any other information that helps you to match application_name to your code. Setting application_name variable in the begging of each transaction allows you to which logical process blocks another one. granted Here's an alternate view of that same data that includes application_name's A database deadlock is a situation in which two or more transactions are waiting for one another to give up locks. transactionid IS NOT DISTINCT FROM blocked_locks. What is a deadlock then As you can imagine, there are several definitions for a database deadlock, but I like the following for its simplicity. database IS NOT DISTINCT FROM blocked_locks. ![]() query AS current_statement_in_blocking_process FROM pg_catalog. When the application flow does not allow for it, you can still explicitly claim pessimistic locks with a SELECT. Practice advice: in order to avoid deadlocks, just ensure that all of your concurrent transactions lock rows in the same order. My thinking is that the original update statement locks all the rows in the table, but my new update statement will lock fewer rows.ĭoes that make sense? Or does the update statement lock the entire table anyway?īy design, any proper RDBMS does not skip rows that would not change (as that would, for example, evade trigger execution), so updating only the rows that need it is always a good idea to avoid nedless I/O (btw, in PG boolean evaluation is native to the parser, you can simply omit the comparison like you would in C or most other bracketed languages: UPDATE big_table SET bool_col = false WHERE bool_col Īlthough the change may mitigate your deadlock problem, keep in mind that what's likely to be happening is that another transaction is locking the same rows as this one, just in a different order, thus creating a lock stalemate (which the postmaster detects and terminates as in your example).įind out what other process is locking any rows that match that update. To: update big_table set bool_col = false where bool_col != false In the f_big_function() function, I am thinking of changing: update big_table set bool_col = false In the f_big_function() function, I have this SQL statement: update big_table set bool_col = false Īlmost all of the values for the bool_col column in big_table are already set to false before the update statement. (47979,12) in relation "big_table" SQL statement "update big_table set bool_col = false" PL/pgSQL function f_big_function() line 691 at SQL statement Im using C3P0 0.9.0.3 with JDK 1.5, Hibernate 3.2, and Postgres 8.1. Process 74331 waits for ShareLock on transaction 140785551 blocked by process 120481. C3p0-users Apparent deadlock with Postgres after resetting the connection pool. I am getting this deadlock: : ERROR: deadlock detected Detail: Process 120481 waits for ShareLock on transaction 140788861 blocked by process 74331.
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