From 07aeb1fec571920839822c11851d38ef48952d6c Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Thu, 5 Dec 2013 12:21:55 -0300
Subject: [PATCH] Avoid resetting Xmax when it's a multi with an aborted update
HeapTupleSatisfiesUpdate can very easily "forget" tuple locks while
checking the contents of a multixact and finding it contains an aborted
update, by setting the HEAP_XMAX_INVALID bit. This would lead to
concurrent transactions not noticing any previous locks held by
transactions that might still be running, and thus being able to acquire
subsequent locks they wouldn't be normally able to acquire.
This bug was introduced in commit 1ce150b7bb; backpatch this fix to 9.3,
like that commit.
This change reverts the change to the delete-abort-savept isolation test
in 1ce150b7bb, because that behavior change was caused by this bug.
Noticed by Andres Freund while investigating a different issue reported
by Noah Misch.
---
src/backend/utils/time/tqual.c | 21 +++++++++++++++----
.../expected/delete-abort-savept.out | 13 +++++-------
2 files changed, 22 insertions(+), 12 deletions(-)
diff --git a/src/backend/utils/time/tqual.c b/src/backend/utils/time/tqual.c
index 1ebc5ff8795..e5d0b0a666e 100644
--- a/src/backend/utils/time/tqual.c
+++ b/src/backend/utils/time/tqual.c
@@ -596,13 +596,26 @@ HeapTupleSatisfiesUpdate(HeapTuple htup, CommandId curcid,
if (TransactionIdDidCommit(xmax))
return HeapTupleUpdated;
- /* no member, even just a locker, alive anymore */
+ /*
+ * By here, the update in the Xmax is either aborted or crashed, but
+ * what about the other members?
+ */
+
if (!MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple)))
+ {
+ /*
+ * There's no member, even just a locker, alive anymore, so we can
+ * mark the Xmax as invalid.
+ */
SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
InvalidTransactionId);
-
- /* it must have aborted or crashed */
- return HeapTupleMayBeUpdated;
+ return HeapTupleMayBeUpdated;
+ }
+ else
+ {
+ /* There are lockers running */
+ return HeapTupleBeingUpdated;
+ }
}
if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(tuple)))
diff --git a/src/test/isolation/expected/delete-abort-savept.out b/src/test/isolation/expected/delete-abort-savept.out
index 5b8c4447284..3420cf47d77 100644
--- a/src/test/isolation/expected/delete-abort-savept.out
+++ b/src/test/isolation/expected/delete-abort-savept.out
@@ -23,11 +23,12 @@ key value
step s1svp: SAVEPOINT f;
step s1d: DELETE FROM foo;
step s1r: ROLLBACK TO f;
-step s2l: SELECT * FROM foo FOR UPDATE;
+step s2l: SELECT * FROM foo FOR UPDATE; <waiting ...>
+step s1c: COMMIT;
+step s2l: <... completed>
key value
1 1
-step s1c: COMMIT;
step s2c: COMMIT;
starting permutation: s1l s1svp s1d s1r s2l s2c s1c
@@ -38,12 +39,8 @@ key value
step s1svp: SAVEPOINT f;
step s1d: DELETE FROM foo;
step s1r: ROLLBACK TO f;
-step s2l: SELECT * FROM foo FOR UPDATE;
-key value
-
-1 1
-step s2c: COMMIT;
-step s1c: COMMIT;
+step s2l: SELECT * FROM foo FOR UPDATE; <waiting ...>
+invalid permutation detected
starting permutation: s1l s1svp s1d s2l s1r s1c s2c
step s1l: SELECT * FROM foo FOR KEY SHARE;
--
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