If MERGE attempts an UPDATE or DELETE on a table with BEFORE ROW
triggers, or a cross-partition UPDATE (with or without triggers), and
a concurrent UPDATE or DELETE happens, the merge code would fail.
In some cases this would lead to a crash, while in others it would
cause the wrong merge action to be executed, or no action at all. The
immediate cause of the crash was the trigger code calling
ExecGetUpdateNewTuple() as part of the EPQ mechanism, which fails
because during a merge ri_projectNew is NULL, since merge has its own
per-action projection information, which ExecGetUpdateNewTuple() knows
nothing about.
Fix by arranging for the trigger code to exit early, returning the
TM_Result and TM_FailureData information, if a concurrent modification
is detected, allowing the merge code to do the necessary EPQ handling
in its own way. Similarly, prevent the cross-partition update code
from doing any EPQ processing for a merge, allowing the merge code to
work out what it needs to do.
This leads to a number of simplifications in nodeModifyTable.c. Most
notably, the ModifyTableContext->GetUpdateNewTuple() callback is no
longer needed, and mergeGetUpdateNewTuple() can be deleted, since
there is no longer any requirement for get-update-new-tuple during a
merge. Similarly, ModifyTableContext->cpUpdateRetrySlot is no longer
needed. Thus ExecGetUpdateNewTuple() and the retry_slot handling of
ExecCrossPartitionUpdate() can be restored to how they were in v14,
before the merge code was added, and ExecMergeMatched() no longer
needs any special-case handling for cross-partition updates.
While at it, tidy up ExecUpdateEpilogue() a bit, making it handle
recheckIndexes locally, rather than passing it in as a parameter,
ensuring that it is freed properly. This dates back to when it was
split off from ExecUpdate() to support merge.
Per bug #17809 from Alexander Lakhin, and follow-up investigation of
bug #17792, also from Alexander Lakhin.
Back-patch to v15, where MERGE was introduced, taking care to preserve
backwards-compatibility of the trigger API in v15 for any extensions
that might use it.
Discussion:
https://postgr.es/m/17809-9e6650bef133f0fe%40postgresql.orghttps://postgr.es/m/17792-0f89452029662c36%40postgresql.org
step delete_tg: DELETE FROM target_tg t WHERE t.key = 1;
step c1: COMMIT;
step update2_tg: UPDATE target_tg t SET val = t.val || ' updated by update2_tg' WHERE t.key = 1;
step select2_tg: SELECT * FROM target_tg;
key|val
---+---
(0 rows)
@ -45,32 +68,72 @@ step c2: COMMIT;
starting permutation: delete c1 merge2 select2 c2
step delete: DELETE FROM target t WHERE t.key = 1;
step c1: COMMIT;
step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2a' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
step delete_pa: DELETE FROM target_pa t WHERE t.key = 1;
step c1: COMMIT;
step merge2_pa: MERGE INTO target_pa t USING (SELECT 1 as key, 'merge2_pa' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
step delete_tg: DELETE FROM target_tg t WHERE t.key = 1;
step c1: COMMIT;
s2: NOTICE: Insert: (1,merge2_tg)
step merge2_tg: MERGE INTO target_tg t USING (SELECT 1 as key, 'merge2_tg' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
step delete: DELETE FROM target t WHERE t.key = 1;
step c1: COMMIT;
step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2a' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
step merge_delete2: MERGE INTO target t USING (SELECT 1 as key, 'merge_delete2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN DELETE;
step delete_tg: DELETE FROM target_tg t WHERE t.key = 1;
step c1: COMMIT;
s2: NOTICE: Insert: (1,merge_delete2_tg)
step merge_delete2_tg: MERGE INTO target_tg t USING (SELECT 1 as key, 'merge_delete2_tg' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN DELETE;
step delete_tg: DELETE FROM target_tg t WHERE t.key = 1;
step update2_tg: UPDATE target_tg t SET val = t.val || ' updated by update2_tg' WHERE t.key = 1; <waiting ...>
step c1: COMMIT;
step update2_tg: <... completed>
step select2_tg: SELECT * FROM target_tg;
key|val
---+---
(0 rows)
@ -92,26 +168,69 @@ step c2: COMMIT;
starting permutation: delete merge2 c1 select2 c2
step delete: DELETE FROM target t WHERE t.key = 1;
step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2a' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val; <waiting ...>
step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val; <waiting ...>
step merge_delete: MERGE INTO target t USING (SELECT 1 as key) s ON s.key = t.key WHEN MATCHED THEN DELETE;
step merge2: MERGE INTO target t USING (SELECT 1 as key, 'merge2a' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val; <waiting ...>
step delete_pa: DELETE FROM target_pa t WHERE t.key = 1;
step merge2_pa: MERGE INTO target_pa t USING (SELECT 1 as key, 'merge2_pa' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val; <waiting ...>
step delete_tg: DELETE FROM target_tg t WHERE t.key = 1;
step merge2_tg: MERGE INTO target_tg t USING (SELECT 1 as key, 'merge2_tg' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val; <waiting ...>
step delete: DELETE FROM target t WHERE t.key = 1;
step merge_delete2: MERGE INTO target t USING (SELECT 1 as key, 'merge_delete2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN DELETE; <waiting ...>
step delete_tg: DELETE FROM target_tg t WHERE t.key = 1;
step merge_delete2_tg: MERGE INTO target_tg t USING (SELECT 1 as key, 'merge_delete2_tg' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN DELETE; <waiting ...>
CREATE TABLE target (key int primary key, val text);
INSERT INTO target VALUES (1, 'setup1');
CREATE TABLE target_pa (key int primary key, val text) PARTITION BY LIST (key);
CREATE TABLE target_pa1 PARTITION OF target_pa FOR VALUES IN (1);
CREATE TABLE target_pa2 PARTITION OF target_pa FOR VALUES IN (2);
INSERT INTO target_pa VALUES (1, 'setup1');
CREATE TABLE target_tg (key int primary key, val text);
CREATE FUNCTION target_tg_trig_fn() RETURNS trigger LANGUAGE plpgsql AS
$$
BEGIN
IF tg_op = 'INSERT' THEN
RAISE NOTICE 'Insert: %', NEW;
RETURN NEW;
ELSIF tg_op = 'UPDATE' THEN
RAISE NOTICE 'Update: % -> %', OLD, NEW;
RETURN NEW;
ELSE
RAISE NOTICE 'Delete: %', OLD;
RETURN OLD;
END IF;
END
$$;
CREATE TRIGGER target_tg_trig BEFORE INSERT OR UPDATE OR DELETE ON target_tg
FOR EACH ROW EXECUTE FUNCTION target_tg_trig_fn();
INSERT INTO target_tg VALUES (1, 'setup1');
}
teardown
{
DROP TABLE target;
DROP TABLE target_pa;
DROP TABLE target_tg;
DROP FUNCTION target_tg_trig_fn;
}
session "s1"
@ -20,7 +48,8 @@ setup
BEGIN ISOLATION LEVEL READ COMMITTED;
}
step "delete" { DELETE FROM target t WHERE t.key = 1; }
step "merge_delete" { MERGE INTO target t USING (SELECT 1 as key) s ON s.key = t.key WHEN MATCHED THEN DELETE; }
step "delete_pa" { DELETE FROM target_pa t WHERE t.key = 1; }
step "delete_tg" { DELETE FROM target_tg t WHERE t.key = 1; }
step "c1" { COMMIT; }
session "s2"
@ -28,23 +57,40 @@ setup
{
BEGIN ISOLATION LEVEL READ COMMITTED;
}
step "update1" { UPDATE target t SET val = t.val || ' updated by update1' WHERE t.key = 1; }
step "merge2" { MERGE INTO target t USING (SELECT 1 as key, 'merge2a' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val; }
step "update2" { UPDATE target t SET val = t.val || ' updated by update2' WHERE t.key = 1; }
step "update2_pa" { UPDATE target_pa t SET val = t.val || ' updated by update2_pa' WHERE t.key = 1; }
step "update2_tg" { UPDATE target_tg t SET val = t.val || ' updated by update2_tg' WHERE t.key = 1; }
step "merge2" { MERGE INTO target t USING (SELECT 1 as key, 'merge2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val; }
step "merge2_pa" { MERGE INTO target_pa t USING (SELECT 1 as key, 'merge2_pa' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val; }
step "merge2_tg" { MERGE INTO target_tg t USING (SELECT 1 as key, 'merge2_tg' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val; }
step "merge_delete2" { MERGE INTO target t USING (SELECT 1 as key, 'merge_delete2' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN DELETE; }
step "merge_delete2_tg" { MERGE INTO target_tg t USING (SELECT 1 as key, 'merge_delete2_tg' as val) s ON s.key = t.key WHEN NOT MATCHED THEN INSERT VALUES (s.key, s.val) WHEN MATCHED THEN DELETE; }
Dean Rasheed
3 years ago