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Commit3cd9c3b

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Fix CREATE INDEX CONCURRENTLY for the newest prepared transactions.
The purpose of commit8a54e12 was tofix this, and it sufficed when the PREPARE TRANSACTION completed beforethe CIC looked for lock conflicts. Otherwise, things still broke. Asbefore, in a cluster having used CIC while having enabled preparedtransactions, queries that use the resulting index can silently fail tofind rows. It may be necessary to reindex to recover from pastoccurrences; REINDEX CONCURRENTLY suffices. Fix this for future indexbuilds by making CIC wait for arbitrarily-recent prepared transactionsand for ordinary transactions that may yet PREPARE TRANSACTION. As partof that, have PREPARE TRANSACTION transfer locks to its dummy PGPROCbefore it calls ProcArrayClearTransaction(). Back-patch to 9.6 (allsupported versions).Andrey Borodin, reviewed (in earlier versions) by Andres Freund.Discussion:https://postgr.es/m/01824242-AA92-4FE9-9BA7-AEBAFFEA3D0C@yandex-team.ru
1 parentfdd965d commit3cd9c3b

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8 files changed

+362
-36
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8 files changed

+362
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‎contrib/amcheck/t/003_cic_2pc.pl

Lines changed: 188 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,188 @@
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# Copyright (c) 2021, PostgreSQL Global Development Group
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# Test CREATE INDEX CONCURRENTLY with concurrent prepared-xact modifications
5+
use strict;
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use warnings;
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use Config;
9+
use PostgresNode;
10+
use TestLib;
11+
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use Test::Moretests=> 6;
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my ($node,$result);
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#
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# Test set-up
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#
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$node = PostgresNode->new('CIC_2PC_test');
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$node->init;
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$node->append_conf('postgresql.conf','max_prepared_transactions = 10');
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$node->append_conf('postgresql.conf','lock_timeout = 180000');
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$node->start;
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$node->safe_psql('postgres',q(CREATE EXTENSION amcheck));
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$node->safe_psql('postgres',q(CREATE TABLE tbl(i int)));
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#
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# Run 3 overlapping 2PC transactions with CIC
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#
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# We have two concurrent background psql processes: $main_h for INSERTs and
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# $cic_h for CIC. Also, we use non-background psql for some COMMIT PREPARED
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# statements.
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#
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my$main_in ='';
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my$main_out ='';
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my$main_timer = IPC::Run::timeout(180);
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my$main_h =
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$node->background_psql('postgres', \$main_in, \$main_out,
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$main_timer,on_error_stop=> 1);
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$main_in .=q(
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BEGIN;
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INSERT INTO tbl VALUES(0);
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\echo syncpoint1
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);
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pump$main_huntil$main_out =~/syncpoint1/ ||$main_timer->is_expired;
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my$cic_in ='';
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my$cic_out ='';
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my$cic_timer = IPC::Run::timeout(180);
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my$cic_h =
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$node->background_psql('postgres', \$cic_in, \$cic_out,
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$cic_timer,on_error_stop=> 1);
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$cic_in .=q(
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\echo start
58+
CREATE INDEX CONCURRENTLY idx ON tbl(i);
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);
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pump$cic_huntil$cic_out =~/start/ ||$cic_timer->is_expired;
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$main_in .=q(
63+
PREPARE TRANSACTION 'a';
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);
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$main_in .=q(
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BEGIN;
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INSERT INTO tbl VALUES(0);
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\echo syncpoint2
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);
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pump$main_huntil$main_out =~/syncpoint2/ ||$main_timer->is_expired;
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$node->safe_psql('postgres',q(COMMIT PREPARED 'a';));
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$main_in .=q(
76+
PREPARE TRANSACTION 'b';
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BEGIN;
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INSERT INTO tbl VALUES(0);
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\echo syncpoint3
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);
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pump$main_huntil$main_out =~/syncpoint3/ ||$main_timer->is_expired;
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$node->safe_psql('postgres',q(COMMIT PREPARED 'b';));
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$main_in .=q(
86+
PREPARE TRANSACTION 'c';
87+
COMMIT PREPARED 'c';
88+
);
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$main_h->pump_nb;
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$main_h->finish;
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$cic_h->finish;
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$result =$node->psql('postgres',q(SELECT bt_index_check('idx',true)));
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is($result,'0','bt_index_check after overlapping 2PC');
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#
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# Server restart shall not change whether prepared xact blocks CIC
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#
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$node->safe_psql(
103+
'postgres',q(
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BEGIN;
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INSERT INTO tbl VALUES(0);
106+
PREPARE TRANSACTION 'spans_restart';
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BEGIN;
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CREATE TABLE unused ();
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PREPARE TRANSACTION 'persists_forever';
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));
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$node->restart;
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my$reindex_in ='';
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my$reindex_out ='';
115+
my$reindex_timer = IPC::Run::timeout(180);
116+
my$reindex_h =
117+
$node->background_psql('postgres', \$reindex_in, \$reindex_out,
118+
$reindex_timer,on_error_stop=> 1);
119+
$reindex_in .=q(
120+
\echo start
121+
DROP INDEX CONCURRENTLY idx;
122+
CREATE INDEX CONCURRENTLY idx ON tbl(i);
123+
);
124+
pump$reindex_huntil$reindex_out =~/start/ ||$reindex_timer->is_expired;
125+
126+
$node->safe_psql('postgres',"COMMIT PREPARED 'spans_restart'");
127+
$reindex_h->finish;
128+
$result =$node->psql('postgres',q(SELECT bt_index_check('idx',true)));
129+
is($result,'0','bt_index_check after 2PC and restart');
130+
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132+
#
133+
# Stress CIC+2PC with pgbench
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#
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136+
# Fix broken index first
137+
$node->safe_psql('postgres',q(REINDEX TABLE tbl;));
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# Run background pgbench with CIC. We cannot mix-in this script into single
140+
# pgbench: CIC will deadlock with itself occasionally.
141+
my$pgbench_out ='';
142+
my$pgbench_timer = IPC::Run::timeout(180);
143+
my$pgbench_h =$node->background_pgbench(
144+
'--no-vacuum --client=1 --transactions=100',
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{
146+
'002_pgbench_concurrent_cic'=>q(
147+
DROP INDEX CONCURRENTLY idx;
148+
CREATE INDEX CONCURRENTLY idx ON tbl(i);
149+
SELECT bt_index_check('idx',true);
150+
)
151+
},
152+
\$pgbench_out,
153+
$pgbench_timer);
154+
155+
# Run pgbench.
156+
$node->pgbench(
157+
'--no-vacuum --client=5 --transactions=100',
158+
0,
159+
[qr{actually processed}],
160+
[qr{^$}],
161+
'concurrent INSERTs w/ 2PC',
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{
163+
'002_pgbench_concurrent_2pc'=>q(
164+
BEGIN;
165+
INSERT INTO tbl VALUES(0);
166+
PREPARE TRANSACTION 'c:client_id';
167+
COMMIT PREPARED 'c:client_id';
168+
),
169+
'002_pgbench_concurrent_2pc_savepoint'=>q(
170+
BEGIN;
171+
SAVEPOINT s1;
172+
INSERT INTO tbl VALUES(0);
173+
PREPARE TRANSACTION 'c:client_id';
174+
COMMIT PREPARED 'c:client_id';
175+
)
176+
});
177+
178+
$pgbench_h->pump_nb;
179+
$pgbench_h->finish();
180+
$result =
181+
($Config{osname}eq"MSWin32")
182+
? ($pgbench_h->full_results)[0]
183+
:$pgbench_h->result(0);
184+
is($result, 0,"pgbench with CIC works");
185+
186+
# done
187+
$node->stop;
188+
done_testing();

‎src/backend/access/transam/twophase.c

Lines changed: 60 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -459,14 +459,24 @@ MarkAsPreparingGuts(GlobalTransaction gxact, TransactionId xid, const char *gid,
459459
proc->pgprocno=gxact->pgprocno;
460460
SHMQueueElemInit(&(proc->links));
461461
proc->waitStatus=PROC_WAIT_STATUS_OK;
462-
/* We set up the gxact's VXID as InvalidBackendId/XID */
463-
proc->lxid= (LocalTransactionId)xid;
462+
if (LocalTransactionIdIsValid(MyProc->lxid))
463+
{
464+
/* clone VXID, for TwoPhaseGetXidByVirtualXID() to find */
465+
proc->lxid=MyProc->lxid;
466+
proc->backendId=MyBackendId;
467+
}
468+
else
469+
{
470+
Assert(AmStartupProcess()|| !IsPostmasterEnvironment);
471+
/* GetLockConflicts() uses this to specify a wait on the XID */
472+
proc->lxid=xid;
473+
proc->backendId=InvalidBackendId;
474+
}
464475
proc->xid=xid;
465476
Assert(proc->xmin==InvalidTransactionId);
466477
proc->delayChkpt= false;
467478
proc->statusFlags=0;
468479
proc->pid=0;
469-
proc->backendId=InvalidBackendId;
470480
proc->databaseId=databaseid;
471481
proc->roleId=owner;
472482
proc->tempNamespaceId=InvalidOid;
@@ -846,6 +856,53 @@ TwoPhaseGetGXact(TransactionId xid, bool lock_held)
846856
returnresult;
847857
}
848858

859+
/*
860+
* TwoPhaseGetXidByVirtualXID
861+
*Lookup VXID among xacts prepared since last startup.
862+
*
863+
* (This won't find recovered xacts.) If more than one matches, return any
864+
* and set "have_more" to true. To witness multiple matches, a single
865+
* BackendId must consume 2^32 LXIDs, with no intervening database restart.
866+
*/
867+
TransactionId
868+
TwoPhaseGetXidByVirtualXID(VirtualTransactionIdvxid,
869+
bool*have_more)
870+
{
871+
inti;
872+
TransactionIdresult=InvalidTransactionId;
873+
874+
Assert(VirtualTransactionIdIsValid(vxid));
875+
LWLockAcquire(TwoPhaseStateLock,LW_SHARED);
876+
877+
for (i=0;i<TwoPhaseState->numPrepXacts;i++)
878+
{
879+
GlobalTransactiongxact=TwoPhaseState->prepXacts[i];
880+
PGPROC*proc;
881+
VirtualTransactionIdproc_vxid;
882+
883+
if (!gxact->valid)
884+
continue;
885+
proc=&ProcGlobal->allProcs[gxact->pgprocno];
886+
GET_VXID_FROM_PGPROC(proc_vxid,*proc);
887+
if (VirtualTransactionIdEquals(vxid,proc_vxid))
888+
{
889+
/* Startup process sets proc->backendId to InvalidBackendId. */
890+
Assert(!gxact->inredo);
891+
892+
if (result!=InvalidTransactionId)
893+
{
894+
*have_more= true;
895+
break;
896+
}
897+
result=gxact->xid;
898+
}
899+
}
900+
901+
LWLockRelease(TwoPhaseStateLock);
902+
903+
returnresult;
904+
}
905+
849906
/*
850907
* TwoPhaseGetDummyBackendId
851908
*Get the dummy backend ID for prepared transaction specified by XID

‎src/backend/access/transam/xact.c

Lines changed: 7 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2506,6 +2506,13 @@ PrepareTransaction(void)
25062506
/* Reset XactLastRecEnd until the next transaction writes something */
25072507
XactLastRecEnd=0;
25082508

2509+
/*
2510+
* Transfer our locks to a dummy PGPROC. This has to be done before
2511+
* ProcArrayClearTransaction(). Otherwise, a GetLockConflicts() would
2512+
* conclude "xact already committed or aborted" for our locks.
2513+
*/
2514+
PostPrepare_Locks(xid);
2515+
25092516
/*
25102517
* Let others know about no transaction in progress by me. This has to be
25112518
* done *after* the prepared transaction has been marked valid, else
@@ -2545,7 +2552,6 @@ PrepareTransaction(void)
25452552

25462553
PostPrepare_MultiXact(xid);
25472554

2548-
PostPrepare_Locks(xid);
25492555
PostPrepare_PredicateLocks(xid);
25502556

25512557
ResourceOwnerRelease(TopTransactionResourceOwner,

‎src/backend/storage/lmgr/lmgr.c

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -871,9 +871,10 @@ XactLockTableWaitErrorCb(void *arg)
871871
* To do this, obtain the current list of lockers, and wait on their VXIDs
872872
* until they are finished.
873873
*
874-
* Note we don't try to acquire the locks on the given locktags, only the VXIDs
875-
* of its lock holders; if somebody grabs a conflicting lock on the objects
876-
* after we obtained our initial list of lockers, we will not wait for them.
874+
* Note we don't try to acquire the locks on the given locktags, only the
875+
* VXIDs and XIDs of their lock holders; if somebody grabs a conflicting lock
876+
* on the objects after we obtained our initial list of lockers, we will not
877+
* wait for them.
877878
*/
878879
void
879880
WaitForLockersMultiple(List*locktags,LOCKMODElockmode,boolprogress)

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