>From fbe641eeb7eb535c1cac422e3f5962928e3b0362 Mon Sep 17 00:00:00 2001 From: Alvaro Herrera Date: Wed, 4 Dec 2013 17:26:07 -0300 Subject: [PATCH 2/4] Fix improper abort during update chain locking In 247c76a98909, I added some code to do fine-grained checking of MultiXact status of locking/updating transactions when traversing an update chain. There was a thinko in that patch which would have the traversing abort, that is return HeapTupleUpdated, when the other transaction is a committed lock-only. In this case we should ignore it and return success instead. Of course, in the case where there is a committed update, HeapTupleUpdated is the correct return value. A user-visible symptom of this bug is that in REPEATABLE READ and SERIALIZABLE transaction isolation modes spurious serializability errors can occur: ERROR: could not serialize access due to concurrent update In order for this to happen, there needs to be a tuple that's key-share- locked and also updated, and the update must abort; a subsequent transaction trying to acquire a new lock on that tuple would abort with the above error. The reason is that the initial FOR KEY SHARE is seen as committed by the new locking transaction, which triggers this bug. The isolation test added by this commit illustrates the desired behavior. Backpatch to 9.3. --- src/backend/access/heap/heapam.c | 19 ++- .../isolation/expected/multixact-no-forget.out | 122 ++++++++++++++++++++ .../isolation/expected/multixact-no-forget_1.out | 118 +++++++++++++++++++ src/test/isolation/specs/multixact-no-forget.spec | 42 +++++++ 4 files changed, 298 insertions(+), 3 deletions(-) create mode 100644 src/test/isolation/expected/multixact-no-forget.out create mode 100644 src/test/isolation/expected/multixact-no-forget_1.out create mode 100644 src/test/isolation/specs/multixact-no-forget.spec diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c index 64174b6..1a0dd21 100644 --- a/src/backend/access/heap/heapam.c +++ b/src/backend/access/heap/heapam.c @@ -4842,10 +4842,23 @@ test_lockmode_for_conflict(MultiXactStatus status, TransactionId xid, else if (TransactionIdDidCommit(xid)) { /* - * If the updating transaction committed, what we do depends on whether - * the lock modes conflict: if they do, then we must report error to - * caller. But if they don't, we can fall through to lock it. + * The other transaction committed. If it was only a locker, then the + * lock is completely gone now and we can return success; but if it + * was an update, then what we do depends on whether the two lock + * modes conflict. If they conflict, then we must report error to + * caller. But if they don't, we can fall through to allow the current + * transaction to lock the tuple. + * + * Note: the reason we worry about ISUPDATE here is because as soon as + * a transaction ends, all its locks are gone and meaningless, and + * thus we can ignore them; whereas its updates persist. In the + * TransactionIdIsInProgress case, above, we don't need to check + * because we know the lock is still "alive" and thus a conflict needs + * always be checked. */ + if (!ISUPDATE_from_mxstatus(status)) + return HeapTupleMayBeUpdated; + if (DoLockModesConflict(LOCKMODE_from_mxstatus(status), LOCKMODE_from_mxstatus(wantedstatus))) /* bummer */ diff --git a/src/test/isolation/expected/multixact-no-forget.out b/src/test/isolation/expected/multixact-no-forget.out new file mode 100644 index 0000000..20f01a6 --- /dev/null +++ b/src/test/isolation/expected/multixact-no-forget.out @@ -0,0 +1,122 @@ +Parsed test spec with 3 sessions + +starting permutation: s1_lock s2_update s2_abort s3_forkeyshr s1_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s2_abort: ROLLBACK; +step s3_forkeyshr: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s1_commit: COMMIT; + +starting permutation: s1_lock s2_update s2_commit s3_forkeyshr s1_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s2_commit: COMMIT; +step s3_forkeyshr: SELECT * FROM dont_forget FOR KEY SHARE; +value + +2 +step s1_commit: COMMIT; + +starting permutation: s1_lock s2_update s1_commit s3_forkeyshr s2_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s1_commit: COMMIT; +step s3_forkeyshr: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_commit: COMMIT; + +starting permutation: s1_lock s2_update s2_abort s3_fornokeyupd s1_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s2_abort: ROLLBACK; +step s3_fornokeyupd: SELECT * FROM dont_forget FOR UPDATE; +step s1_commit: COMMIT; +step s3_fornokeyupd: <... completed> +value + +1 + +starting permutation: s1_lock s2_update s2_commit s3_fornokeyupd s1_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s2_commit: COMMIT; +step s3_fornokeyupd: SELECT * FROM dont_forget FOR UPDATE; +step s1_commit: COMMIT; +step s3_fornokeyupd: <... completed> +value + +2 + +starting permutation: s1_lock s2_update s1_commit s3_fornokeyupd s2_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s1_commit: COMMIT; +step s3_fornokeyupd: SELECT * FROM dont_forget FOR UPDATE; +step s2_commit: COMMIT; +step s3_fornokeyupd: <... completed> +value + +2 + +starting permutation: s1_lock s2_update s2_abort s3_forupd s1_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s2_abort: ROLLBACK; +step s3_forupd: SELECT * FROM dont_forget FOR NO KEY UPDATE; +value + +1 +step s1_commit: COMMIT; + +starting permutation: s1_lock s2_update s2_commit s3_forupd s1_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s2_commit: COMMIT; +step s3_forupd: SELECT * FROM dont_forget FOR NO KEY UPDATE; +value + +2 +step s1_commit: COMMIT; + +starting permutation: s1_lock s2_update s1_commit s3_forupd s2_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s1_commit: COMMIT; +step s3_forupd: SELECT * FROM dont_forget FOR NO KEY UPDATE; +step s2_commit: COMMIT; +step s3_forupd: <... completed> +value + +2 diff --git a/src/test/isolation/expected/multixact-no-forget_1.out b/src/test/isolation/expected/multixact-no-forget_1.out new file mode 100644 index 0000000..7c0adcf --- /dev/null +++ b/src/test/isolation/expected/multixact-no-forget_1.out @@ -0,0 +1,118 @@ +Parsed test spec with 3 sessions + +starting permutation: s1_lock s2_update s2_abort s3_forkeyshr s1_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s2_abort: ROLLBACK; +step s3_forkeyshr: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s1_commit: COMMIT; + +starting permutation: s1_lock s2_update s2_commit s3_forkeyshr s1_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s2_commit: COMMIT; +step s3_forkeyshr: SELECT * FROM dont_forget FOR KEY SHARE; +value + +2 +step s1_commit: COMMIT; + +starting permutation: s1_lock s2_update s1_commit s3_forkeyshr s2_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s1_commit: COMMIT; +step s3_forkeyshr: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_commit: COMMIT; + +starting permutation: s1_lock s2_update s2_abort s3_fornokeyupd s1_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s2_abort: ROLLBACK; +step s3_fornokeyupd: SELECT * FROM dont_forget FOR UPDATE; +step s1_commit: COMMIT; +step s3_fornokeyupd: <... completed> +value + +1 + +starting permutation: s1_lock s2_update s2_commit s3_fornokeyupd s1_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s2_commit: COMMIT; +step s3_fornokeyupd: SELECT * FROM dont_forget FOR UPDATE; +step s1_commit: COMMIT; +step s3_fornokeyupd: <... completed> +value + +2 + +starting permutation: s1_lock s2_update s1_commit s3_fornokeyupd s2_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s1_commit: COMMIT; +step s3_fornokeyupd: SELECT * FROM dont_forget FOR UPDATE; +step s2_commit: COMMIT; +step s3_fornokeyupd: <... completed> +error in steps s2_commit s3_fornokeyupd: ERROR: could not serialize access due to concurrent update + +starting permutation: s1_lock s2_update s2_abort s3_forupd s1_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s2_abort: ROLLBACK; +step s3_forupd: SELECT * FROM dont_forget FOR NO KEY UPDATE; +value + +1 +step s1_commit: COMMIT; + +starting permutation: s1_lock s2_update s2_commit s3_forupd s1_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s2_commit: COMMIT; +step s3_forupd: SELECT * FROM dont_forget FOR NO KEY UPDATE; +value + +2 +step s1_commit: COMMIT; + +starting permutation: s1_lock s2_update s1_commit s3_forupd s2_commit +step s1_lock: SELECT * FROM dont_forget FOR KEY SHARE; +value + +1 +step s2_update: UPDATE dont_forget SET value = 2; +step s1_commit: COMMIT; +step s3_forupd: SELECT * FROM dont_forget FOR NO KEY UPDATE; +step s2_commit: COMMIT; +step s3_forupd: <... completed> +error in steps s2_commit s3_forupd: ERROR: could not serialize access due to concurrent update diff --git a/src/test/isolation/specs/multixact-no-forget.spec b/src/test/isolation/specs/multixact-no-forget.spec new file mode 100644 index 0000000..c1cfb7c --- /dev/null +++ b/src/test/isolation/specs/multixact-no-forget.spec @@ -0,0 +1,42 @@ +# If transaction A holds a lock, and transaction B does an update, +# make sure we don't forget the lock if B aborts. +setup +{ + CREATE TABLE dont_forget ( + value int + ); + + INSERT INTO dont_forget VALUES (1); +} + +teardown +{ + DROP TABLE dont_forget; +} + +session "s1" +setup { BEGIN; } +step "s1_lock" { SELECT * FROM dont_forget FOR KEY SHARE; } +step "s1_commit" { COMMIT; } + +session "s2" +setup { BEGIN; } +step "s2_update" { UPDATE dont_forget SET value = 2; } +step "s2_abort" { ROLLBACK; } +step "s2_commit" { COMMIT; } + +session "s3" +# try cases with both a non-conflicting lock with s1's and a conflicting one +step "s3_forkeyshr" { SELECT * FROM dont_forget FOR KEY SHARE; } +step "s3_fornokeyupd" { SELECT * FROM dont_forget FOR UPDATE; } +step "s3_forupd" { SELECT * FROM dont_forget FOR NO KEY UPDATE; } + +permutation "s1_lock" "s2_update" "s2_abort" "s3_forkeyshr" "s1_commit" +permutation "s1_lock" "s2_update" "s2_commit" "s3_forkeyshr" "s1_commit" +permutation "s1_lock" "s2_update" "s1_commit" "s3_forkeyshr" "s2_commit" +permutation "s1_lock" "s2_update" "s2_abort" "s3_fornokeyupd" "s1_commit" +permutation "s1_lock" "s2_update" "s2_commit" "s3_fornokeyupd" "s1_commit" +permutation "s1_lock" "s2_update" "s1_commit" "s3_fornokeyupd" "s2_commit" +permutation "s1_lock" "s2_update" "s2_abort" "s3_forupd" "s1_commit" +permutation "s1_lock" "s2_update" "s2_commit" "s3_forupd" "s1_commit" +permutation "s1_lock" "s2_update" "s1_commit" "s3_forupd" "s2_commit" -- 1.7.10.4