doc:  clarify when row-level locks are released
They are released just like table-level locks.  Also clean up wording.
(Uses wording "rolled back to".)
Reported-by:
Discussion:
Backpatch-through: 9.5
@@ -1039,7 +1039,7 @@ ERROR: could not serialize access due to read/write dependencies among transact
</tip>
<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
immediately if the savepoint is rolled back to. This is consistent with
the principle that <command>ROLLBACK</command> cancels all effects of the
@@ -1178,7 +1178,10 @@ ERROR: could not serialize access due to read/write dependencies among transact
conflicting locks on the same row, even in different subtransactions;
but other than that, two transactions can never hold conflicting locks
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>
<variablelist>
