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Commit10ea0f9

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Expose some information about backend subxact status.
A new function pg_stat_get_backend_subxact() can be used to getinformation about the number of subtransactions in the cache ofa particular backend and whether that cache has overflowed. Thiscan be useful for tracking down performance problems that canresult from overflowed snapshots.Dilip Kumar, reviewed by Zhihong Yu, Nikolay Samokhvalov,Justin Pryzby, Nathan Bossart, Ashutosh Sharma, JulienRouhaud. Additional design comments from Andres Freund,Tom Lane, Bruce Momjian, and David G. Johnston.Discussion:http://postgr.es/m/CAFiTN-ut0uwkRJDQJeDPXpVyTWD46m3gt3JDToE02hTfONEN=Q@mail.gmail.com
1 parent7122f9d commit10ea0f9

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8 files changed

+90
-7
lines changed

8 files changed

+90
-7
lines changed

‎doc/src/sgml/monitoring.sgml

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -5671,6 +5671,24 @@ FROM pg_stat_get_backend_idset() AS backendid;
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</para></entry>
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</row>
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5674+
<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>pg_stat_get_backend_subxact</primary>
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</indexterm>
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<function>pg_stat_get_backend_subxact</function> ( <type>integer</type> )
5680+
<returnvalue>record</returnvalue>
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</para>
5682+
<para>
5683+
Returns a record of information about the subtransactions of the
5684+
backend with the specified ID.
5685+
The fields returned are <parameter>subxact_count</parameter>, which
5686+
is the number of subtransactions in the backend's subtransaction cache,
5687+
and <parameter>subxact_overflow</parameter>, which indicates whether
5688+
the backend's subtransaction cache is overflowed or not.
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</para></entry>
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</row>
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56745692
<row>
56755693
<entry role="func_table_entry"><para role="func_signature">
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<indexterm>

‎src/backend/storage/ipc/sinvaladt.c

Lines changed: 9 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -404,17 +404,20 @@ BackendIdGetProc(int backendID)
404404

405405
/*
406406
* BackendIdGetTransactionIds
407-
*Get the xidandxminof the backend. The result may be out of date
408-
*arbitrarily quickly, so the caller must be careful about how this
409-
*information is used.
407+
*Get the xid, xmin, nsubxidandoverflow statusof the backend. The
408+
*result may be out of datearbitrarily quickly, so the caller must be
409+
*careful about how thisinformation is used.
410410
*/
411411
void
412-
BackendIdGetTransactionIds(intbackendID,TransactionId*xid,TransactionId*xmin)
412+
BackendIdGetTransactionIds(intbackendID,TransactionId*xid,
413+
TransactionId*xmin,int*nsubxid,bool*overflowed)
413414
{
414415
SISeg*segP=shmInvalBuffer;
415416

416417
*xid=InvalidTransactionId;
417418
*xmin=InvalidTransactionId;
419+
*nsubxid=0;
420+
*overflowed= false;
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419422
/* Need to lock out additions/removals of backends */
420423
LWLockAcquire(SInvalWriteLock,LW_SHARED);
@@ -428,6 +431,8 @@ BackendIdGetTransactionIds(int backendID, TransactionId *xid, TransactionId *xmi
428431
{
429432
*xid=proc->xid;
430433
*xmin=proc->xmin;
434+
*nsubxid=proc->subxidStatus.count;
435+
*overflowed=proc->subxidStatus.overflowed;
431436
}
432437
}
433438

‎src/backend/utils/activity/backend_status.c

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -855,7 +855,9 @@ pgstat_read_current_status(void)
855855
localentry->backend_id=i;
856856
BackendIdGetTransactionIds(i,
857857
&localentry->backend_xid,
858-
&localentry->backend_xmin);
858+
&localentry->backend_xmin,
859+
&localentry->backend_subxact_count,
860+
&localentry->backend_subxact_overflowed);
859861

860862
localentry++;
861863
localappname+=NAMEDATALEN;

‎src/backend/utils/adt/pgstatfuncs.c

Lines changed: 38 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -687,6 +687,44 @@ pg_stat_get_backend_userid(PG_FUNCTION_ARGS)
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PG_RETURN_OID(beentry->st_userid);
688688
}
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690+
Datum
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pg_stat_get_backend_subxact(PG_FUNCTION_ARGS)
692+
{
693+
#definePG_STAT_GET_SUBXACT_COLS2
694+
TupleDesctupdesc;
695+
Datumvalues[PG_STAT_GET_SUBXACT_COLS];
696+
boolnulls[PG_STAT_GET_SUBXACT_COLS];
697+
int32beid=PG_GETARG_INT32(0);
698+
LocalPgBackendStatus*local_beentry;
699+
700+
/* Initialise values and NULL flags arrays */
701+
MemSet(values,0,sizeof(values));
702+
MemSet(nulls,0,sizeof(nulls));
703+
704+
/* Initialise attributes information in the tuple descriptor */
705+
tupdesc=CreateTemplateTupleDesc(PG_STAT_GET_SUBXACT_COLS);
706+
TupleDescInitEntry(tupdesc, (AttrNumber)1,"subxact_count",
707+
INT4OID,-1,0);
708+
TupleDescInitEntry(tupdesc, (AttrNumber)2,"subxact_overflow",
709+
BOOLOID,-1,0);
710+
711+
BlessTupleDesc(tupdesc);
712+
713+
if ((local_beentry=pgstat_fetch_stat_local_beentry(beid))!=NULL)
714+
{
715+
/* Fill values and NULLs */
716+
values[0]=Int32GetDatum(local_beentry->backend_subxact_count);
717+
values[1]=BoolGetDatum(local_beentry->backend_subxact_overflowed);
718+
}
719+
else
720+
{
721+
nulls[0]= true;
722+
nulls[1]= true;
723+
}
724+
725+
/* Returns the record as Datum */
726+
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc,values,nulls)));
727+
}
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691729
Datum
692730
pg_stat_get_backend_activity(PG_FUNCTION_ARGS)

‎src/include/catalog/catversion.h

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -57,6 +57,6 @@
5757
*/
5858

5959
/*yyyymmddN */
60-
#defineCATALOG_VERSION_NO202212131
60+
#defineCATALOG_VERSION_NO202212191
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#endif

‎src/include/catalog/pg_proc.dat

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -5441,6 +5441,13 @@
54415441
proname => 'pg_stat_get_backend_dbid', provolatile => 's', proparallel => 'r',
54425442
prorettype => 'oid', proargtypes => 'int4',
54435443
prosrc => 'pg_stat_get_backend_dbid' },
5444+
{ oid => '6107', descr => 'statistics: get subtransaction status of backend',
5445+
proname => 'pg_stat_get_backend_subxact', provolatile => 's', proparallel => 'r',
5446+
prorettype => 'record', proargtypes => 'int4',
5447+
proallargtypes => '{int4,int4,bool}',
5448+
proargmodes => '{i,o,o}',
5449+
proargnames => '{bid,subxact_count,subxact_overflowed}',
5450+
prosrc => 'pg_stat_get_backend_subxact' },
54445451
{ oid => '1939', descr => 'statistics: user ID of backend',
54455452
proname => 'pg_stat_get_backend_userid', provolatile => 's',
54465453
proparallel => 'r', prorettype => 'oid', proargtypes => 'int4',

‎src/include/storage/sinvaladt.h

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -32,7 +32,9 @@ extern Size SInvalShmemSize(void);
3232
externvoidCreateSharedInvalidationState(void);
3333
externvoidSharedInvalBackendInit(boolsendOnly);
3434
externPGPROC*BackendIdGetProc(intbackendID);
35-
externvoidBackendIdGetTransactionIds(intbackendID,TransactionId*xid,TransactionId*xmin);
35+
externvoidBackendIdGetTransactionIds(intbackendID,TransactionId*xid,
36+
TransactionId*xmin,int*nsubxid,
37+
bool*overflowed);
3638

3739
externvoidSIInsertDataEntries(constSharedInvalidationMessage*data,intn);
3840
externintSIGetDataEntries(SharedInvalidationMessage*data,intdatasize);

‎src/include/utils/backend_status.h

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -266,6 +266,17 @@ typedef struct LocalPgBackendStatus
266266
* not.
267267
*/
268268
TransactionIdbackend_xmin;
269+
270+
/*
271+
* Number of cached subtransactions in the current session.
272+
*/
273+
intbackend_subxact_count;
274+
275+
/*
276+
* The number of subtransactions in the current session exceeded the cached
277+
* subtransaction limit.
278+
*/
279+
boolbackend_subxact_overflowed;
269280
}LocalPgBackendStatus;
270281

271282

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