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Fix FOR UPDATE NOWAIT on updated tuple chains 

If SELECT FOR UPDATE NOWAIT tries to lock a tuple that is concurrently
being updated, it might fail to honor its NOWAIT specification and block
instead of raising an error.

Fix by adding a no-wait flag to EvalPlanQualFetch which it can pass down
to heap_lock_tuple; also use it in EvalPlanQualFetch itself to avoid
blocking while waiting for a concurrent transaction.

Authors: Craig Ringer and Thomas Munro, tweaked by Álvaro
http://www.postgresql.org/message-id/51FB6703.9090801@2ndquadrant.com

Per Thomas Munro in the course of his SKIP LOCKED feature submission,
who also provided one of the isolation test specs.

Backpatch to 9.4, because that's as far back as it applies without
conflicts (although the bug goes all the way back).  To that branch also
backpatch Thomas Munro's new NOWAIT test cases, committed in master by
Heikki as commit 9ee16b49f0 .
This commit is contained in:
Alvaro Herrera 2014-08-27 19:15:18 -04:00
parent 9a2d94892f
commit 1c9701cfe5
9 changed files with 186 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
src/backend/executor/execMain.c
View File

@ -1863,7 +1863,7 @@ EvalPlanQual(EState *estate, EPQState *epqstate,
/*
* Get and lock the updated version of the row; if fail, return NULL.
*/
copyTuple = EvalPlanQualFetch(estate, relation, lockmode,
copyTuple = EvalPlanQualFetch(estate, relation, lockmode, false /* wait */,
tid, priorXmax);
if (copyTuple == NULL)
@ -1922,6 +1922,7 @@ EvalPlanQual(EState *estate, EPQState *epqstate,
* estate - executor state data
* relation - table containing tuple
* lockmode - requested tuple lock mode
* noWait - wait mode to pass to heap_lock_tuple
* *tid - t_ctid from the outdated tuple (ie, next updated version)
* priorXmax - t_xmax from the outdated tuple
*
@ -1934,7 +1935,7 @@ EvalPlanQual(EState *estate, EPQState *epqstate,
* but we use "int" to avoid having to include heapam.h in executor.h.
*/
HeapTuple
EvalPlanQualFetch(EState *estate, Relation relation, int lockmode,
EvalPlanQualFetch(EState *estate, Relation relation, int lockmode, bool noWait,
ItemPointer tid, TransactionId priorXmax)
{
HeapTuple copyTuple = NULL;
@ -1978,14 +1979,23 @@ EvalPlanQualFetch(EState *estate, Relation relation, int lockmode,
/*
* If tuple is being updated by other transaction then we have to
* wait for its commit/abort.
* wait for its commit/abort, or die trying.
*/
if (TransactionIdIsValid(SnapshotDirty.xmax))
{
ReleaseBuffer(buffer);
XactLockTableWait(SnapshotDirty.xmax,
relation, &tuple.t_data->t_ctid,
XLTW_FetchUpdated);
if (noWait)
{
if (!ConditionalXactLockTableWait(SnapshotDirty.xmax))
ereport(ERROR,
(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
errmsg("could not obtain lock on row in relation \"%s\"",
RelationGetRelationName(relation))));
}
else
XactLockTableWait(SnapshotDirty.xmax,
relation, &tuple.t_data->t_ctid,
XLTW_FetchUpdated);
continue; /* loop back to repeat heap_fetch */
}
@ -2012,7 +2022,7 @@ EvalPlanQualFetch(EState *estate, Relation relation, int lockmode,
*/
test = heap_lock_tuple(relation, &tuple,
estate->es_output_cid,
lockmode, false /* wait */ ,
lockmode, noWait,
false, &buffer, &hufd);
/* We now have two pins on the buffer, get rid of one */
ReleaseBuffer(buffer);

2
src/backend/executor/nodeLockRows.c
View File

@ -170,7 +170,7 @@ lnext:
}
/* updated, so fetch and lock the updated version */
copyTuple = EvalPlanQualFetch(estate, erm->relation, lockmode,
copyTuple = EvalPlanQualFetch(estate, erm->relation, lockmode, erm->noWait,
&hufd.ctid, hufd.xmax);
if (copyTuple == NULL)

2
src/include/executor/executor.h
View File

@ -199,7 +199,7 @@ extern TupleTableSlot *EvalPlanQual(EState *estate, EPQState *epqstate,
Relation relation, Index rti, int lockmode,
ItemPointer tid, TransactionId priorXmax);
extern HeapTuple EvalPlanQualFetch(EState *estate, Relation relation,
int lockmode, ItemPointer tid, TransactionId priorXmax);
int lockmode, bool noWait, ItemPointer tid, TransactionId priorXmax);
extern void EvalPlanQualInit(EPQState *epqstate, EState *estate,
Plan *subplan, List *auxrowmarks, int epqParam);
extern void EvalPlanQualSetPlan(EPQState *epqstate,

19
src/test/isolation/expected/nowait-4.out Normal file
View File

@ -0,0 +1,19 @@
Parsed test spec with 2 sessions
starting permutation: s2a s1a s2b s2c s2d s2e s1b s2f
step s2a: SELECT pg_advisory_lock(0);
pg_advisory_lock
step s1a: SELECT * FROM foo WHERE pg_advisory_lock(0) IS NOT NULL FOR UPDATE NOWAIT; <waiting ...>
step s2b: UPDATE foo SET data = data;
step s2c: BEGIN;
step s2d: UPDATE foo SET data = data;
step s2e: SELECT pg_advisory_unlock(0);
pg_advisory_unlock
t
step s1a: <... completed>
error in steps s2e s1a: ERROR: could not obtain lock on row in relation "foo"
step s1b: COMMIT;
step s2f: COMMIT;

19
src/test/isolation/expected/nowait-4_1.out Normal file
View File

@ -0,0 +1,19 @@
Parsed test spec with 2 sessions
starting permutation: s2a s1a s2b s2c s2d s2e s1b s2f
step s2a: SELECT pg_advisory_lock(0);
pg_advisory_lock
step s1a: SELECT * FROM foo WHERE pg_advisory_lock(0) IS NOT NULL FOR UPDATE NOWAIT; <waiting ...>
step s2b: UPDATE foo SET data = data;
step s2c: BEGIN;
step s2d: UPDATE foo SET data = data;
step s2e: SELECT pg_advisory_unlock(0);
pg_advisory_unlock
t
step s1a: <... completed>
error in steps s2e s1a: ERROR: could not serialize access due to concurrent update
step s1b: COMMIT;
step s2f: COMMIT;

37
src/test/isolation/expected/nowait-5.out Normal file
View File

@ -0,0 +1,37 @@
Parsed test spec with 3 sessions
starting permutation: sl1_prep upd_getlock sl1_exec upd_doupdate lk1_doforshare upd_releaselock
step sl1_prep:
PREPARE sl1_run AS SELECT id FROM test_nowait WHERE pg_advisory_lock(0) is not null FOR UPDATE NOWAIT;
step upd_getlock:
SELECT pg_advisory_lock(0);
pg_advisory_lock
step sl1_exec:
BEGIN ISOLATION LEVEL READ COMMITTED;
EXECUTE sl1_run;
SELECT xmin, xmax, ctid, * FROM test_nowait;
<waiting ...>
step upd_doupdate:
BEGIN ISOLATION LEVEL READ COMMITTED;
UPDATE test_nowait SET value = value WHERE id % 2 = 0;
COMMIT;
step lk1_doforshare:
BEGIN ISOLATION LEVEL READ COMMITTED;
SELECT id FROM test_nowait WHERE id % 2 = 0 FOR SHARE;
id
2
step upd_releaselock:
SELECT pg_advisory_unlock(0);
pg_advisory_unlock
t
step sl1_exec: <... completed>
error in steps upd_releaselock sl1_exec: ERROR: could not obtain lock on row in relation "test_nowait"

8
src/test/isolation/isolation_schedule
View File

@ -22,9 +22,11 @@ test: aborted-keyrevoke
test: multixact-no-deadlock
test: multixact-no-forget
test: propagate-lock-delete
test: drop-index-concurrently-1
test: alter-table-1
test: timeouts
test: nowait
test: nowait-2
test: nowait-3
test: nowait-4
test: nowait-5
test: drop-index-concurrently-1
test: alter-table-1
test: timeouts

30
src/test/isolation/specs/nowait-4.spec Normal file
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@ -0,0 +1,30 @@
# Test NOWAIT with an updated tuple chain.
setup
{
CREATE TABLE foo (
id int PRIMARY KEY,
data text NOT NULL
);
INSERT INTO foo VALUES (1, 'x');
}
teardown
{
DROP TABLE foo;
}
session "s1"
setup { BEGIN; }
step "s1a" { SELECT * FROM foo WHERE pg_advisory_lock(0) IS NOT NULL FOR UPDATE NOWAIT; }
step "s1b" { COMMIT; }
session "s2"
step "s2a" { SELECT pg_advisory_lock(0); }
step "s2b" { UPDATE foo SET data = data; }
step "s2c" { BEGIN; }
step "s2d" { UPDATE foo SET data = data; }
step "s2e" { SELECT pg_advisory_unlock(0); }
step "s2f" { COMMIT; }
permutation "s2a" "s1a" "s2b" "s2c" "s2d" "s2e" "s1b" "s2f"

57
src/test/isolation/specs/nowait-5.spec Normal file
View File

@ -0,0 +1,57 @@
# Test NOWAIT on an updated tuple chain
setup
{
DROP TABLE IF EXISTS test_nowait;
CREATE TABLE test_nowait (
id integer PRIMARY KEY,
value integer not null
);
INSERT INTO test_nowait
SELECT x,x FROM generate_series(1,2) x;
}
teardown
{
DROP TABLE test_nowait;
}
session "sl1"
step "sl1_prep" {
PREPARE sl1_run AS SELECT id FROM test_nowait WHERE pg_advisory_lock(0) is not null FOR UPDATE NOWAIT;
}
step "sl1_exec" {
BEGIN ISOLATION LEVEL READ COMMITTED;
EXECUTE sl1_run;
SELECT xmin, xmax, ctid, * FROM test_nowait;
}
teardown { COMMIT; }
# A session that's used for an UPDATE of the rows to be locked, for when we're testing ctid
# chain following.
session "upd"
step "upd_getlock" {
SELECT pg_advisory_lock(0);
}
step "upd_doupdate" {
BEGIN ISOLATION LEVEL READ COMMITTED;
UPDATE test_nowait SET value = value WHERE id % 2 = 0;
COMMIT;
}
step "upd_releaselock" {
SELECT pg_advisory_unlock(0);
}
# A session that acquires locks that sl1 is supposed to avoid blocking on
session "lk1"
step "lk1_doforshare" {
BEGIN ISOLATION LEVEL READ COMMITTED;
SELECT id FROM test_nowait WHERE id % 2 = 0 FOR SHARE;
}
teardown {
COMMIT;
}
permutation "sl1_prep" "upd_getlock" "sl1_exec" "upd_doupdate" "lk1_doforshare" "upd_releaselock"