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doc: clarify when row-level locks are released

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They are released just like table-level locks.  Also clean up wording.

Reported-by: me@sillymon.ch

Discussion: https://postgr.es/m/158074944048.1095.4309647363871637715@wrigleys.postgresql.org

Backpatch-through: 9.5
This commit is contained in:
Bruce Momjian 2020-03-31 17:27:32 -04:00
parent ce5d82f2d0
commit 6e727a13cb
1 changed files with 6 additions and 3 deletions
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9
doc/src/sgml/mvcc.sgml
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@ -1035,9 +1035,9 @@ ERROR: could not serialize access due to read/write dependencies among transact
</tip> </tip>
<para> <para>
Once acquired, a lock is normally held till end of transaction. But if a Once acquired, a lock is normally held until the end of the transaction. But if a
lock is acquired after establishing a savepoint, the lock is released lock is acquired after establishing a savepoint, the lock is released
immediately if the savepoint is rolled back to. This is consistent with immediately if the savepoint is rolled back. This is consistent with
the principle that <command>ROLLBACK</> cancels all effects of the the principle that <command>ROLLBACK</> cancels all effects of the
commands since the savepoint. The same holds for locks acquired within a commands since the savepoint. The same holds for locks acquired within a
<application>PL/pgSQL</> exception block: an error escape from the block <application>PL/pgSQL</> exception block: an error escape from the block
@ -1174,7 +1174,10 @@ ERROR: could not serialize access due to read/write dependencies among transact
conflicting locks on the same row, even in different subtransactions; conflicting locks on the same row, even in different subtransactions;
but other than that, two transactions can never hold conflicting locks but other than that, two transactions can never hold conflicting locks
on the same row. Row-level locks do not affect data querying; they on the same row. Row-level locks do not affect data querying; they
block only <emphasis>writers and lockers</emphasis> to the same row. block only <emphasis>writers and lockers</emphasis> to the same
row. Row-level locks are released at transaction end or during
savepoint rollback, just like table-level locks.
</para> </para>
<variablelist> <variablelist>