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peterepetere
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Fix snapshot leak warning for some procedures
The problem arises with the combination of CALL with output parameters and doing a COMMIT inside the procedure. When a CALL has output parameters, the portal uses the strategy PORTAL_UTIL_SELECT instead of PORTAL_MULTI_QUERY. Using PORTAL_UTIL_SELECT causes the portal's snapshot to be registered with the current resource owner (portal->holdSnapshot); see 9ee1cf0 for the reason. Normally, PortalDrop() unregisters the snapshot. If not, then ResourceOwnerRelease() will print a warning about a snapshot leak on transaction commit. A transaction commit normally drops all portals (PreCommit_Portals()), except the active portal. So in case of the active portal, we need to manually release the snapshot to avoid the warning. Reported-by: Prabhat Sahu <[email protected]> Reviewed-by: Jonathan S. Katz <[email protected]>
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3 files changed

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‎src/backend/utils/mmgr/portalmem.c

Lines changed: 12 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -689,13 +689,23 @@ PreCommit_Portals(bool isPrepare)
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/*
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* Do not touch active portals --- this can only happen in the case of
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* a multi-transaction utility command, such as VACUUM.
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* a multi-transaction utility command, such as VACUUM, or a commit in
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* a procedure.
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*
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* Note however that any resource owner attached to such a portal is
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* still going to go away, so don't leave a dangling pointer.
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* still going to go away, so don't leave a dangling pointer. Also
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* unregister any snapshots held by the portal, mainly to avoid
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* snapshot leak warnings from ResourceOwnerRelease().
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*/
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if (portal->status == PORTAL_ACTIVE)
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{
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if (portal->holdSnapshot)
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{
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if (portal->resowner)
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UnregisterSnapshotFromOwner(portal->holdSnapshot,
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portal->resowner);
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portal->holdSnapshot = NULL;
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}
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portal->resowner = NULL;
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continue;
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}

‎src/pl/plpgsql/src/expected/plpgsql_transaction.out

Lines changed: 30 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -463,6 +463,36 @@ SELECT * FROM test2;
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42
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(1 row)
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-- Test transaction in procedure with output parameters. This uses a
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-- different portal strategy and different code paths in pquery.c.
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CREATE PROCEDURE transaction_test10a(INOUT x int)
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LANGUAGE plpgsql
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AS $$
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BEGIN
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x := x + 1;
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COMMIT;
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END;
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$$;
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CALL transaction_test10a(10);
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x
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----
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11
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(1 row)
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CREATE PROCEDURE transaction_test10b(INOUT x int)
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LANGUAGE plpgsql
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AS $$
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BEGIN
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x := x - 1;
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ROLLBACK;
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END;
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$$;
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CALL transaction_test10b(10);
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x
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---
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9
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(1 row)
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DROP TABLE test1;
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DROP TABLE test2;
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DROP TABLE test3;

‎src/pl/plpgsql/src/sql/plpgsql_transaction.sql

Lines changed: 25 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -387,6 +387,31 @@ $$;
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SELECT * FROM test2;
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-- Test transaction in procedure with output parameters. This uses a
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-- different portal strategy and different code paths in pquery.c.
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CREATE PROCEDURE transaction_test10a(INOUT x int)
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LANGUAGE plpgsql
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AS $$
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BEGIN
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x := x + 1;
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COMMIT;
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END;
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$$;
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CALL transaction_test10a(10);
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CREATE PROCEDURE transaction_test10b(INOUT x int)
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LANGUAGE plpgsql
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AS $$
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BEGIN
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x := x - 1;
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ROLLBACK;
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END;
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$$;
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CALL transaction_test10b(10);
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DROP TABLE test1;
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DROP TABLE test2;
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DROP TABLE test3;

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