How do Postgres locks work?
Locks or Exclusive Locks or Write Locks prevent users from modifying a row or an entire table. Rows modified by UPDATE and DELETE are then exclusively locked automatically for the duration of the transaction. This prevents other users from changing the row until the transaction is either committed or rolled back.
What is PG lock?
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How does the lock queue work in PostgreSQL?
One other thing to be aware of is that Postgres uses lock queues. If you run an ALTER TABLE command then that command goes into the queue and blocks until all queries on that table are finished, but any SELECT that comes immediately after will be blocked until the ALTER TABLE is finished even if the ALTER TABLE is not yet running.
Do you need to block reads or writes in PostgreSQL?
However, not all DDL commands need to block reads or writes, some only block each other. Whether a transaction can acquire a lock depends on whether its “lock level” conflicts with that of the holder (s) of the lock. The PostgreSQL documentation gives a detailed overview of how different lock levels conflict.
Which is the best lock mode for PostgreSQL?
Explicit Locking 1 13.3.1. Table-level Locks. The list below shows the available lock modes and the contexts in which they are used automatically by PostgreSQL. 2 13.3.2. Row-level Locks. 3 13.3.3. Page-level Locks. 4 13.3.4. Deadlocks. 5 13.3.5. Advisory Locks.
Is the access exclusive lock self-conflicting in PostgreSQL?
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). Conflicts with the ACCESS EXCLUSIVE lock mode only.