![]() ![]() #Postgres deadlock update#EXCLUSIVE ( ExclusiveLock)Ĭonflicts with the ROW SHARE, ROW EXCLUSIVE, SHARE UPDATE EXCLUSIVE, SHARE, SHARE ROW EXCLUSIVE, EXCLUSIVE, and ACCESS EXCLUSIVE lock modes. This mode protects a table against concurrent data changes, and is self-exclusive so that only one session can hold it at a time.Īcquired by CREATE TRIGGER and some forms of ALTER TABLE. SHARE ROW EXCLUSIVE ( ShareRowExclusiveLock)Ĭonflicts with the ROW EXCLUSIVE, SHARE UPDATE EXCLUSIVE, SHARE, SHARE ROW EXCLUSIVE, EXCLUSIVE, and ACCESS EXCLUSIVE lock modes. This mode protects a table against concurrent data changes.Īcquired by CREATE INDEX (without CONCURRENTLY). SHARE ( ShareLock)Ĭonflicts with the ROW EXCLUSIVE, SHARE UPDATE EXCLUSIVE, SHARE ROW EXCLUSIVE, EXCLUSIVE, and ACCESS EXCLUSIVE lock modes. #Postgres deadlock full#This mode protects a table against concurrent schema changes and VACUUM runs.Īcquired by VACUUM (without FULL), ANALYZE, CREATE INDEX CONCURRENTLY, CREATE STATISTICS, COMMENT ON, REINDEX CONCURRENTLY, and certain ALTER INDEX and ALTER TABLE variants (for full details see the documentation of these commands). ![]() SHARE UPDATE EXCLUSIVE ( ShareUpdateExclusiveLock)Ĭonflicts with the SHARE UPDATE EXCLUSIVE, SHARE, SHARE ROW EXCLUSIVE, EXCLUSIVE, and ACCESS EXCLUSIVE lock modes. In general, this lock mode will be acquired by any command that modifies data in a table. The commands UPDATE, DELETE, and INSERT acquire this lock mode on the target table (in addition to ACCESS SHARE locks on any other referenced tables). ROW EXCLUSIVE ( RowExclusiveLock)Ĭonflicts with the SHARE, SHARE ROW EXCLUSIVE, EXCLUSIVE, and ACCESS EXCLUSIVE lock modes. The SELECT FOR UPDATE and SELECT FOR SHARE commands acquire a lock of this mode on the target table(s) (in addition to ACCESS SHARE locks on any other tables that are referenced but not selected FOR UPDATE/FOR SHARE). ROW SHARE ( RowShareLock)Ĭonflicts with the EXCLUSIVE and ACCESS EXCLUSIVE lock modes. In general, any query that only reads a table and does not modify it will acquire this lock mode. The SELECT command acquires a lock of this mode on referenced tables. Table-Level Lock Modes ACCESS SHARE ( AccessShareLock)Ĭonflicts with the ACCESS EXCLUSIVE lock mode only. Notice in particular that some lock modes are self-conflicting (for example, an ACCESS EXCLUSIVE lock cannot be held by more than one transaction at a time) while others are not self-conflicting (for example, an ACCESS SHARE lock can be held by multiple transactions). For example, it might acquire ACCESS EXCLUSIVE lock and later acquire ACCESS SHARE lock on the same table.) Non-conflicting lock modes can be held concurrently by many transactions. (However, a transaction never conflicts with itself. Two transactions cannot hold locks of conflicting modes on the same table at the same time. The only real difference between one lock mode and another is the set of lock modes with which each conflicts (see Table 13.2). ![]() To some extent the names reflect the typical usage of each lock mode - but the semantics are all the same. Remember that all of these lock modes are table-level locks, even if the name contains the word “ row” the names of the lock modes are historical. You can also acquire any of these locks explicitly with the command LOCK. You should start to consider upgrading.Ī deadlock situation involving VACUUM should have been fixed in 8.3.1.The list below shows the available lock modes and the contexts in which they are used automatically by PostgreSQL. The deadlock to the server log (Itagaki Takahiro)Īlso, version 8.3 will meet its end of life in February 2013. When reporting a deadlock, report the text of all queries involved in In particular this improvement in version 8.4 should be interesting for you ( quoting the release notes): ![]() #Postgres deadlock manual#The manual provides the basic strategy to solve most cases in the chapter about deadlocks.Īs for version 8.3: consider upgrading to a more recent version. If all your clients access resources in a synchronized order, deadlocks cannot occur. To alleviate deadlocks, you can do a number of things. Remove the EXCEPTION block from your plpgsql function, if you don't get the information in the db log and try again. The fact that you catch the error may prevent Postgres from giving you the full details. Both processes that compete for resources are listed in detail with standard logging settings. Modern versions raise a detailed error message. See comment by below, who is an expert on concurrency in PostgreSQL. A function like you display can never deadlock itself. There is definitely some other process competing for the same resource. ![]()
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