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Commit3d092fe

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Avoid unnecessary catalog updates in ALTER SEQUENCE
ALTER SEQUENCE can do nontransactional changes to the sequence (RESTARTclause) and transactional updates to the pg_sequence catalog (most otherclauses). When just calling RESTART, the code would still needlessly doa catalog update without any changes. This would entangle thatoperation in the concurrency issues of a catalog update (causing eitherlocking or concurrency errors, depending on how that issue is to beresolved).Fix by keeping track during options parsing whether a catalog update isneeded, and skip it if not.Reported-by: Jason Petersen <jason@citusdata.com>
1 parenta35ac7c commit3d092fe

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+43
-8
lines changed

1 file changed

+43
-8
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‎src/backend/commands/sequence.c

Lines changed: 43 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -101,6 +101,7 @@ static Form_pg_sequence_data read_seq_tuple(Relation rel,
101101
staticvoidinit_params(ParseState*pstate,List*options,boolfor_identity,
102102
boolisInit,
103103
Form_pg_sequenceseqform,
104+
bool*changed_seqform,
104105
Form_pg_sequence_dataseqdataform,List**owned_by);
105106
staticvoiddo_setval(Oidrelid,int64next,booliscalled);
106107
staticvoidprocess_owned_by(Relationseqrel,List*owned_by,boolfor_identity);
@@ -115,6 +116,7 @@ DefineSequence(ParseState *pstate, CreateSeqStmt *seq)
115116
{
116117
FormData_pg_sequenceseqform;
117118
FormData_pg_sequence_dataseqdataform;
119+
boolchanged_seqform= false;/* not used here */
118120
List*owned_by;
119121
CreateStmt*stmt=makeNode(CreateStmt);
120122
Oidseqoid;
@@ -153,7 +155,7 @@ DefineSequence(ParseState *pstate, CreateSeqStmt *seq)
153155
}
154156

155157
/* Check and set all option values */
156-
init_params(pstate,seq->options,seq->for_identity, true,&seqform,&seqdataform,&owned_by);
158+
init_params(pstate,seq->options,seq->for_identity, true,&seqform,&changed_seqform,&seqdataform,&owned_by);
157159

158160
/*
159161
* Create relation (and fill value[] and null[] for the tuple)
@@ -418,6 +420,7 @@ AlterSequence(ParseState *pstate, AlterSeqStmt *stmt)
418420
Form_pg_sequenceseqform;
419421
Form_pg_sequence_dataseqdata;
420422
FormData_pg_sequence_datanewseqdata;
423+
boolchanged_seqform= false;
421424
List*owned_by;
422425
ObjectAddressaddress;
423426
Relationrel;
@@ -443,7 +446,7 @@ AlterSequence(ParseState *pstate, AlterSeqStmt *stmt)
443446
/* lock page' buffer and read tuple into new sequence structure */
444447
seqdata=read_seq_tuple(seqrel,&buf,&seqdatatuple);
445448

446-
/* Copy oldvalues of options into workspace */
449+
/* Copy oldsequence data into workspace */
447450
memcpy(&newseqdata,seqdata,sizeof(FormData_pg_sequence_data));
448451

449452
rel=heap_open(SequenceRelationId,RowExclusiveLock);
@@ -456,7 +459,7 @@ AlterSequence(ParseState *pstate, AlterSeqStmt *stmt)
456459
seqform= (Form_pg_sequence)GETSTRUCT(tuple);
457460

458461
/* Check and set new values */
459-
init_params(pstate,stmt->options,stmt->for_identity, false,seqform,&newseqdata,&owned_by);
462+
init_params(pstate,stmt->options,stmt->for_identity, false,seqform,&changed_seqform,&newseqdata,&owned_by);
460463

461464
/* Clear local cache so that we don't think we have cached numbers */
462465
/* Note that we do not change the currval() state */
@@ -507,7 +510,8 @@ AlterSequence(ParseState *pstate, AlterSeqStmt *stmt)
507510

508511
relation_close(seqrel,NoLock);
509512

510-
CatalogTupleUpdate(rel,&tuple->t_self,tuple);
513+
if (changed_seqform)
514+
CatalogTupleUpdate(rel,&tuple->t_self,tuple);
511515
heap_close(rel,RowExclusiveLock);
512516

513517
returnaddress;
@@ -1213,9 +1217,12 @@ read_seq_tuple(Relation rel, Buffer *buf, HeapTuple seqdatatuple)
12131217
}
12141218

12151219
/*
1216-
* init_params: process the options list of CREATE or ALTER SEQUENCE,
1217-
* and store the values into appropriate fields of *new. Also set
1218-
* *owned_by to any OWNED BY option, or to NIL if there is none.
1220+
* init_params: process the options list of CREATE or ALTER SEQUENCE, and
1221+
* store the values into appropriate fields of seqform, for changes that go
1222+
* into the pg_sequence catalog, and seqdataform for changes to the sequence
1223+
* relation itself. Set *changed_seqform to true if seqform was changed
1224+
* (interesting for ALTER SEQUENCE). Also set *owned_by to any OWNED BY
1225+
* option, or to NIL if there is none.
12191226
*
12201227
* If isInit is true, fill any unspecified options with default values;
12211228
* otherwise, do not change existing options that aren't explicitly overridden.
@@ -1224,7 +1231,9 @@ static void
12241231
init_params(ParseState*pstate,List*options,boolfor_identity,
12251232
boolisInit,
12261233
Form_pg_sequenceseqform,
1227-
Form_pg_sequence_dataseqdataform,List**owned_by)
1234+
bool*changed_seqform,
1235+
Form_pg_sequence_dataseqdataform,
1236+
List**owned_by)
12281237
{
12291238
DefElem*as_type=NULL;
12301239
DefElem*start_value=NULL;
@@ -1342,6 +1351,8 @@ init_params(ParseState *pstate, List *options, bool for_identity,
13421351
defel->defname);
13431352
}
13441353

1354+
*changed_seqform= false;
1355+
13451356
/*
13461357
* We must reset log_cnt when isInit or when changing any parameters that
13471358
* would affect future nextval allocations.
@@ -1382,37 +1393,50 @@ init_params(ParseState *pstate, List *options, bool for_identity,
13821393
}
13831394

13841395
seqform->seqtypid=newtypid;
1396+
*changed_seqform= true;
13851397
}
13861398
elseif (isInit)
1399+
{
13871400
seqform->seqtypid=INT8OID;
1401+
*changed_seqform= true;
1402+
}
13881403

13891404
/* INCREMENT BY */
13901405
if (increment_by!=NULL)
13911406
{
13921407
seqform->seqincrement=defGetInt64(increment_by);
1408+
*changed_seqform= true;
13931409
if (seqform->seqincrement==0)
13941410
ereport(ERROR,
13951411
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
13961412
errmsg("INCREMENT must not be zero")));
13971413
seqdataform->log_cnt=0;
13981414
}
13991415
elseif (isInit)
1416+
{
14001417
seqform->seqincrement=1;
1418+
*changed_seqform= true;
1419+
}
14011420

14021421
/* CYCLE */
14031422
if (is_cycled!=NULL)
14041423
{
14051424
seqform->seqcycle=intVal(is_cycled->arg);
1425+
*changed_seqform= true;
14061426
Assert(BoolIsValid(seqform->seqcycle));
14071427
seqdataform->log_cnt=0;
14081428
}
14091429
elseif (isInit)
1430+
{
14101431
seqform->seqcycle= false;
1432+
*changed_seqform= true;
1433+
}
14111434

14121435
/* MAXVALUE (null arg means NO MAXVALUE) */
14131436
if (max_value!=NULL&&max_value->arg)
14141437
{
14151438
seqform->seqmax=defGetInt64(max_value);
1439+
*changed_seqform= true;
14161440
seqdataform->log_cnt=0;
14171441
}
14181442
elseif (isInit||max_value!=NULL||reset_max_value)
@@ -1429,6 +1453,7 @@ init_params(ParseState *pstate, List *options, bool for_identity,
14291453
}
14301454
else
14311455
seqform->seqmax=-1;/* descending seq */
1456+
*changed_seqform= true;
14321457
seqdataform->log_cnt=0;
14331458
}
14341459

@@ -1450,6 +1475,7 @@ init_params(ParseState *pstate, List *options, bool for_identity,
14501475
if (min_value!=NULL&&min_value->arg)
14511476
{
14521477
seqform->seqmin=defGetInt64(min_value);
1478+
*changed_seqform= true;
14531479
seqdataform->log_cnt=0;
14541480
}
14551481
elseif (isInit||min_value!=NULL||reset_min_value)
@@ -1466,6 +1492,7 @@ init_params(ParseState *pstate, List *options, bool for_identity,
14661492
}
14671493
else
14681494
seqform->seqmin=1;/* ascending seq */
1495+
*changed_seqform= true;
14691496
seqdataform->log_cnt=0;
14701497
}
14711498

@@ -1499,13 +1526,17 @@ init_params(ParseState *pstate, List *options, bool for_identity,
14991526

15001527
/* START WITH */
15011528
if (start_value!=NULL)
1529+
{
15021530
seqform->seqstart=defGetInt64(start_value);
1531+
*changed_seqform= true;
1532+
}
15031533
elseif (isInit)
15041534
{
15051535
if (seqform->seqincrement>0)
15061536
seqform->seqstart=seqform->seqmin;/* ascending seq */
15071537
else
15081538
seqform->seqstart=seqform->seqmax;/* descending seq */
1539+
*changed_seqform= true;
15091540
}
15101541

15111542
/* crosscheck START */
@@ -1580,6 +1611,7 @@ init_params(ParseState *pstate, List *options, bool for_identity,
15801611
if (cache_value!=NULL)
15811612
{
15821613
seqform->seqcache=defGetInt64(cache_value);
1614+
*changed_seqform= true;
15831615
if (seqform->seqcache <=0)
15841616
{
15851617
charbuf[100];
@@ -1593,7 +1625,10 @@ init_params(ParseState *pstate, List *options, bool for_identity,
15931625
seqdataform->log_cnt=0;
15941626
}
15951627
elseif (isInit)
1628+
{
15961629
seqform->seqcache=1;
1630+
*changed_seqform= true;
1631+
}
15971632
}
15981633

15991634
/*

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