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Does PostgreSQL support row level locking?
The lock is held until the transaction commits or rolls back, just like table-level locks. Row-level locks do not affect data querying; they block only writers to the same row. PostgreSQL doesn’t remember any information about modified rows in memory, so there is no limit on the number of rows locked at one time.
The AccessShareLock that is created for read queries like the select statements, and AccessExclusiveLock that is created for operations that modify the whole table. There are several more lock modes in PostgreSQL. ACCESS SHARE — Acquired by queries that only read from a table but do not modify it.
Is there a row level lock in PostgreSQL?
Note that this will lock the entire table and referring to PostgreSQL there is no table level lock that can lock exclusively a specific row. row level lock in all your SELECT that will update your row and this will prevent all those SELECT that will update a row from reading your row !
What happens if you roll back PostgreSQL update?
Else the UPDATE now finds no qualifying row and does nothing, returning no row, so the INSERT also does nothing. If rolled back, lock the row and proceed. There is no potential for a race condition. There is no potential for a deadlock unless you put more writes into the same transaction or otherwise lock more rows than just the one.
When to use access exclusive lock in Postgres?
FOR UPDATE in BLOCK2 before end the first transaction. It will be waiting the first transaction to end and will select right after it. Only an ACCESS EXCLUSIVE lock blocks a SELECT (without FOR UPDATE/SHARE) statement. I am using it in a function to control subsequences and it is great.
What does locking in PostgreSQL mean for transactions?
This prevents them from being locked, modified or deleted by other transactions until the current transaction ends.