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Commit07ee62c

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Propagate xactStartTimestamp and stmtStartTimestamp to parallel workers.
Previously, a worker process would establish values for these based onits own start time. In v10 and up, this can trivially be shown to causemisbehavior of transaction_timestamp(), timestamp_in(), and relatedfunctions which are (perhaps unwisely?) marked parallel-safe. It seemslikely that other behaviors might diverge from what happens in the parentas well.It's not as trivial to demonstrate problems in 9.6 or 9.5, but I'm sureit's still possible, so back-patch to all branches containing parallelworker infrastructure.In HEAD only, mark now() and statement_timestamp() as parallel-safe(other affected functions already were). While in theory we couldstill squeeze that change into v11, it doesn't seem important enoughto force a last-minute catversion bump.Konstantin Knizhnik, whacked around a bit by meDiscussion:https://postgr.es/m/6406dbd2-5d37-4cb6-6eb2-9c44172c7e7c@postgrespro.ru
1 parente954a72 commit07ee62c

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5 files changed

+52
-10
lines changed

5 files changed

+52
-10
lines changed

‎src/backend/access/transam/parallel.c

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -87,6 +87,8 @@ typedef struct FixedParallelState
8787
PGPROC*parallel_master_pgproc;
8888
pid_tparallel_master_pid;
8989
BackendIdparallel_master_backend_id;
90+
TimestampTzxact_ts;
91+
TimestampTzstmt_ts;
9092

9193
/* Mutex protects remaining fields. */
9294
slock_tmutex;
@@ -318,6 +320,8 @@ InitializeParallelDSM(ParallelContext *pcxt)
318320
fps->parallel_master_pgproc=MyProc;
319321
fps->parallel_master_pid=MyProcPid;
320322
fps->parallel_master_backend_id=MyBackendId;
323+
fps->xact_ts=GetCurrentTransactionStartTimestamp();
324+
fps->stmt_ts=GetCurrentStatementStartTimestamp();
321325
SpinLockInit(&fps->mutex);
322326
fps->last_xlog_end=0;
323327
shm_toc_insert(pcxt->toc,PARALLEL_KEY_FIXED,fps);
@@ -1311,6 +1315,13 @@ ParallelWorkerMain(Datum main_arg)
13111315
fps->parallel_master_pid))
13121316
return;
13131317

1318+
/*
1319+
* Restore transaction and statement start-time timestamps. This must
1320+
* happen before anything that would start a transaction, else asserts in
1321+
* xact.c will fire.
1322+
*/
1323+
SetParallelStartTimestamps(fps->xact_ts,fps->stmt_ts);
1324+
13141325
/*
13151326
* Identify the entry point to be called. In theory this could result in
13161327
* loading an additional library, though most likely the entry point is in

‎src/backend/access/transam/xact.c

Lines changed: 32 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -674,6 +674,22 @@ GetCurrentCommandId(bool used)
674674
returncurrentCommandId;
675675
}
676676

677+
/*
678+
*SetParallelStartTimestamps
679+
*
680+
* In a parallel worker, we should inherit the parent transaction's
681+
* timestamps rather than setting our own. The parallel worker
682+
* infrastructure must call this to provide those values before
683+
* calling StartTransaction() or SetCurrentStatementStartTimestamp().
684+
*/
685+
void
686+
SetParallelStartTimestamps(TimestampTzxact_ts,TimestampTzstmt_ts)
687+
{
688+
Assert(IsParallelWorker());
689+
xactStartTimestamp=xact_ts;
690+
stmtStartTimestamp=stmt_ts;
691+
}
692+
677693
/*
678694
*GetCurrentTransactionStartTimestamp
679695
*/
@@ -708,11 +724,17 @@ GetCurrentTransactionStopTimestamp(void)
708724

709725
/*
710726
*SetCurrentStatementStartTimestamp
727+
*
728+
* In a parallel worker, this should already have been provided by a call
729+
* to SetParallelStartTimestamps().
711730
*/
712731
void
713732
SetCurrentStatementStartTimestamp(void)
714733
{
715-
stmtStartTimestamp=GetCurrentTimestamp();
734+
if (!IsParallelWorker())
735+
stmtStartTimestamp=GetCurrentTimestamp();
736+
else
737+
Assert(stmtStartTimestamp!=0);
716738
}
717739

718740
/*
@@ -1867,10 +1889,16 @@ StartTransaction(void)
18671889
/*
18681890
* set transaction_timestamp() (a/k/a now()). We want this to be the same
18691891
* as the first command's statement_timestamp(), so don't do a fresh
1870-
* GetCurrentTimestamp() call (which'd be expensive anyway). Also, mark
1871-
* xactStopTimestamp as unset.
1892+
* GetCurrentTimestamp() call (which'd be expensive anyway). In a
1893+
* parallel worker, this should already have been provided by a call to
1894+
* SetParallelStartTimestamps().
1895+
*
1896+
* Also, mark xactStopTimestamp as unset.
18721897
*/
1873-
xactStartTimestamp=stmtStartTimestamp;
1898+
if (!IsParallelWorker())
1899+
xactStartTimestamp=stmtStartTimestamp;
1900+
else
1901+
Assert(xactStartTimestamp!=0);
18741902
xactStopTimestamp=0;
18751903
pgstat_report_xact_timestamp(xactStartTimestamp);
18761904

‎src/include/access/xact.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -359,6 +359,7 @@ extern SubTransactionId GetCurrentSubTransactionId(void);
359359
externvoidMarkCurrentTransactionIdLoggedIfAny(void);
360360
externboolSubTransactionIsActive(SubTransactionIdsubxid);
361361
externCommandIdGetCurrentCommandId(boolused);
362+
externvoidSetParallelStartTimestamps(TimestampTzxact_ts,TimestampTzstmt_ts);
362363
externTimestampTzGetCurrentTransactionStartTimestamp(void);
363364
externTimestampTzGetCurrentStatementStartTimestamp(void);
364365
externTimestampTzGetCurrentTransactionStopTimestamp(void);

‎src/include/catalog/catversion.h

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -53,6 +53,6 @@
5353
*/
5454

5555
/*yyyymmddN */
56-
#defineCATALOG_VERSION_NO201810051
56+
#defineCATALOG_VERSION_NO201810061
5757

5858
#endif

‎src/include/catalog/pg_proc.dat

Lines changed: 7 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -2073,7 +2073,8 @@
20732073
{ oid => '1365', descr => 'make ACL item',
20742074
proname => 'makeaclitem', prorettype => 'aclitem',
20752075
proargtypes => 'oid oid text bool', prosrc => 'makeaclitem' },
2076-
{ oid => '3943', descr => 'show hardwired default privileges, primarily for use by the information schema',
2076+
{ oid => '3943',
2077+
descr => 'show hardwired default privileges, primarily for use by the information schema',
20772078
proname => 'acldefault', prorettype => '_aclitem', proargtypes => 'char oid',
20782079
prosrc => 'acldefault_sql' },
20792080
{ oid => '1689',
@@ -2595,13 +2596,13 @@
25952596
proname => 'timetzdate_pl', prolang => '14', prorettype => 'timestamptz',
25962597
proargtypes => 'timetz date', prosrc => 'select ($2 + $1)' },
25972598
{ oid => '1299', descr => 'current transaction time',
2598-
proname => 'now', provolatile => 's',proparallel => 'r',
2599-
prorettype => 'timestamptz',proargtypes => '', prosrc => 'now' },
2599+
proname => 'now', provolatile => 's',prorettype => 'timestamptz',
2600+
proargtypes => '', prosrc => 'now' },
26002601
{ oid => '2647', descr => 'current transaction time',
26012602
proname => 'transaction_timestamp', provolatile => 's',
26022603
prorettype => 'timestamptz', proargtypes => '', prosrc => 'now' },
26032604
{ oid => '2648', descr => 'current statement time',
2604-
proname => 'statement_timestamp', provolatile => 's', proparallel => 'r',
2605+
proname => 'statement_timestamp', provolatile => 's',
26052606
prorettype => 'timestamptz', proargtypes => '',
26062607
prosrc => 'statement_timestamp' },
26072608
{ oid => '2649', descr => 'current clock time',
@@ -10208,7 +10209,8 @@
1020810209
proname => 'pg_ls_tmpdir', procost => '10', prorows => '20', proretset => 't',
1020910210
provolatile => 'v', prorettype => 'record', proargtypes => 'oid',
1021010211
proallargtypes => '{oid,text,int8,timestamptz}', proargmodes => '{i,o,o,o}',
10211-
proargnames => '{tablespace,name,size,modification}', prosrc => 'pg_ls_tmpdir_1arg' },
10212+
proargnames => '{tablespace,name,size,modification}',
10213+
prosrc => 'pg_ls_tmpdir_1arg' },
1021210214

1021310215
# hash partitioning constraint function
1021410216
{ oid => '5028', descr => 'hash partition CHECK constraint',

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