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Commit3d79013

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Make ALTER SEQUENCE, including RESTART, fully transactional.
Previously the changes to the "data" part of the sequence, i.e. theone containing the current value, were not transactional, whereas thedefinition, including minimum and maximum value were. That leads toodd behaviour if a schema change is rolled back, with the potentialthat out-of-bound sequence values can be returned.To avoid the issue create a new relfilenode fork whenever ALTERSEQUENCE is executed, similar to how TRUNCATE ... RESTART IDENTITYalready is already handled.This commit also makes ALTER SEQUENCE RESTART transactional, as itseems to be too confusing to have some forms of ALTER SEQUENCE behavetransactionally, some forms not. This way setval() and nextval() arenot transactional, but DDL is, which seems to make sense.This commit also rolls back parts of the changes made in3d092feandf8dc198 as they're now not needed anymore.Author: Andres FreundDiscussion:https://postgr.es/m/20170522154227.nvafbsm62sjpbxvd@alap3.anarazel.deBackpatch: Bug is in master/v10 only
1 parente9a3c04 commit3d79013

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4 files changed

+65
-122
lines changed

4 files changed

+65
-122
lines changed

‎doc/src/sgml/ref/alter_sequence.sgml

Lines changed: 7 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -171,7 +171,7 @@ ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> S
171171
<para>
172172
The optional clause <literal>RESTART [ WITH <replaceable
173173
class="parameter">restart</replaceable> ]</literal> changes the
174-
current value of the sequence. This isequivalent to calling the
174+
current value of the sequence. This issimilar to calling the
175175
<function>setval</> function with <literal>is_called</literal> =
176176
<literal>false</>: the specified value will be returned by the
177177
<emphasis>next</> call of <function>nextval</>.
@@ -182,11 +182,11 @@ ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> S
182182
</para>
183183

184184
<para>
185-
Likea <function>setval</function> call, a <literal>RESTART</literal>
186-
operation on a sequence isnever rolled back, to avoid blocking of
187-
concurrent transactionsthat obtain numbers from the same sequence.
188-
(The other clauses cause ordinary catalog updates that can be rolled
189-
back.)
185+
In contrast toa <function>setval</function> call,
186+
a <literal>RESTART</literal>operation on a sequence istransactional
187+
and blocksconcurrent transactionsfrom obtaining numbers from the
188+
same sequence. If that's not the desired mode of
189+
operation, <function>setval</> should be used.
190190
</para>
191191
</listitem>
192192
</varlistentry>
@@ -307,8 +307,7 @@ ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> S
307307
<para>
308308
<command>ALTER SEQUENCE</command> blocks
309309
concurrent <function>nextval</function>, <function>currval</function>,
310-
<function>lastval</function>, and <command>setval</command> calls, except
311-
if only the <literal>RESTART</literal> clause is used.
310+
<function>lastval</function>, and <command>setval</command> calls.
312311
</para>
313312

314313
<para>

‎src/backend/commands/sequence.c

Lines changed: 32 additions & 91 deletions
Original file line numberDiff line numberDiff line change
@@ -98,11 +98,9 @@ static void create_seq_hashtable(void);
9898
staticvoidinit_sequence(Oidrelid,SeqTable*p_elm,Relation*p_rel);
9999
staticForm_pg_sequence_dataread_seq_tuple(Relationrel,
100100
Buffer*buf,HeapTupleseqdatatuple);
101-
staticLOCKMODEalter_sequence_get_lock_level(List*options);
102101
staticvoidinit_params(ParseState*pstate,List*options,boolfor_identity,
103102
boolisInit,
104103
Form_pg_sequenceseqform,
105-
bool*changed_seqform,
106104
Form_pg_sequence_dataseqdataform,List**owned_by);
107105
staticvoiddo_setval(Oidrelid,int64next,booliscalled);
108106
staticvoidprocess_owned_by(Relationseqrel,List*owned_by,boolfor_identity);
@@ -117,7 +115,6 @@ DefineSequence(ParseState *pstate, CreateSeqStmt *seq)
117115
{
118116
FormData_pg_sequenceseqform;
119117
FormData_pg_sequence_dataseqdataform;
120-
boolchanged_seqform= false;/* not used here */
121118
List*owned_by;
122119
CreateStmt*stmt=makeNode(CreateStmt);
123120
Oidseqoid;
@@ -156,7 +153,7 @@ DefineSequence(ParseState *pstate, CreateSeqStmt *seq)
156153
}
157154

158155
/* Check and set all option values */
159-
init_params(pstate,seq->options,seq->for_identity, true,&seqform,&changed_seqform,&seqdataform,&owned_by);
156+
init_params(pstate,seq->options,seq->for_identity, true,&seqform,&seqdataform,&owned_by);
160157

161158
/*
162159
* Create relation (and fill value[] and null[] for the tuple)
@@ -417,19 +414,18 @@ AlterSequence(ParseState *pstate, AlterSeqStmt *stmt)
417414
SeqTableelm;
418415
Relationseqrel;
419416
Bufferbuf;
420-
HeapTupleDataseqdatatuple;
417+
HeapTupleDatadatatuple;
421418
Form_pg_sequenceseqform;
422-
Form_pg_sequence_dataseqdata;
423-
FormData_pg_sequence_datanewseqdata;
424-
boolchanged_seqform= false;
419+
Form_pg_sequence_datanewdataform;
425420
List*owned_by;
426421
ObjectAddressaddress;
427422
Relationrel;
428-
HeapTupletuple;
423+
HeapTupleseqtuple;
424+
HeapTuplenewdatatuple;
429425

430426
/* Open and lock sequence. */
431427
relid=RangeVarGetRelid(stmt->sequence,
432-
alter_sequence_get_lock_level(stmt->options),
428+
ShareRowExclusiveLock,
433429
stmt->missing_ok);
434430
if (relid==InvalidOid)
435431
{
@@ -447,22 +443,26 @@ AlterSequence(ParseState *pstate, AlterSeqStmt *stmt)
447443
stmt->sequence->relname);
448444

449445
rel=heap_open(SequenceRelationId,RowExclusiveLock);
450-
tuple=SearchSysCacheCopy1(SEQRELID,
451-
ObjectIdGetDatum(relid));
452-
if (!HeapTupleIsValid(tuple))
446+
seqtuple=SearchSysCacheCopy1(SEQRELID,
447+
ObjectIdGetDatum(relid));
448+
if (!HeapTupleIsValid(seqtuple))
453449
elog(ERROR,"cache lookup failed for sequence %u",
454450
relid);
455451

456-
seqform= (Form_pg_sequence)GETSTRUCT(tuple);
452+
seqform= (Form_pg_sequence)GETSTRUCT(seqtuple);
457453

458454
/* lock page's buffer and read tuple into new sequence structure */
459-
seqdata=read_seq_tuple(seqrel,&buf,&seqdatatuple);
455+
(void)read_seq_tuple(seqrel,&buf,&datatuple);
460456

461-
/* Copy old sequence data into workspace */
462-
memcpy(&newseqdata,seqdata,sizeof(FormData_pg_sequence_data));
457+
/* copy the existing sequence data tuple, so it can be modified localy */
458+
newdatatuple=heap_copytuple(&datatuple);
459+
newdataform= (Form_pg_sequence_data)GETSTRUCT(newdatatuple);
460+
461+
UnlockReleaseBuffer(buf);
463462

464463
/* Check and set new values */
465-
init_params(pstate,stmt->options,stmt->for_identity, false,seqform,&changed_seqform,&newseqdata,&owned_by);
464+
init_params(pstate,stmt->options,stmt->for_identity, false,seqform,
465+
newdataform,&owned_by);
466466

467467
/* Clear local cache so that we don't think we have cached numbers */
468468
/* Note that we do not change the currval() state */
@@ -472,36 +472,19 @@ AlterSequence(ParseState *pstate, AlterSeqStmt *stmt)
472472
if (RelationNeedsWAL(seqrel))
473473
GetTopTransactionId();
474474

475-
/* Now okay to update the on-disk tuple */
476-
START_CRIT_SECTION();
477-
478-
memcpy(seqdata,&newseqdata,sizeof(FormData_pg_sequence_data));
479-
480-
MarkBufferDirty(buf);
481-
482-
/* XLOG stuff */
483-
if (RelationNeedsWAL(seqrel))
484-
{
485-
xl_seq_recxlrec;
486-
XLogRecPtrrecptr;
487-
Pagepage=BufferGetPage(buf);
488-
489-
XLogBeginInsert();
490-
XLogRegisterBuffer(0,buf,REGBUF_WILL_INIT);
491-
492-
xlrec.node=seqrel->rd_node;
493-
XLogRegisterData((char*)&xlrec,sizeof(xl_seq_rec));
494-
495-
XLogRegisterData((char*)seqdatatuple.t_data,seqdatatuple.t_len);
496-
497-
recptr=XLogInsert(RM_SEQ_ID,XLOG_SEQ_LOG);
498-
499-
PageSetLSN(page,recptr);
500-
}
501-
502-
END_CRIT_SECTION();
475+
/*
476+
* Create a new storage file for the sequence, making the state changes
477+
* transactional. We want to keep the sequence's relfrozenxid at 0, since
478+
* it won't contain any unfrozen XIDs. Same with relminmxid, since a
479+
* sequence will never contain multixacts.
480+
*/
481+
RelationSetNewRelfilenode(seqrel,seqrel->rd_rel->relpersistence,
482+
InvalidTransactionId,InvalidMultiXactId);
503483

504-
UnlockReleaseBuffer(buf);
484+
/*
485+
* Insert the modified tuple into the new storage file.
486+
*/
487+
fill_seq_with_data(seqrel,newdatatuple);
505488

506489
/* process OWNED BY if given */
507490
if (owned_by)
@@ -511,10 +494,9 @@ AlterSequence(ParseState *pstate, AlterSeqStmt *stmt)
511494

512495
ObjectAddressSet(address,RelationRelationId,relid);
513496

514-
if (changed_seqform)
515-
CatalogTupleUpdate(rel,&tuple->t_self,tuple);
516-
heap_close(rel,RowExclusiveLock);
497+
CatalogTupleUpdate(rel,&seqtuple->t_self,seqtuple);
517498

499+
heap_close(rel,RowExclusiveLock);
518500
relation_close(seqrel,NoLock);
519501

520502
returnaddress;
@@ -1219,30 +1201,6 @@ read_seq_tuple(Relation rel, Buffer *buf, HeapTuple seqdatatuple)
12191201
returnseq;
12201202
}
12211203

1222-
/*
1223-
* Check the sequence options list and return the appropriate lock level for
1224-
* ALTER SEQUENCE.
1225-
*
1226-
* Most sequence option changes require a self-exclusive lock and should block
1227-
* concurrent nextval() et al. But RESTART does not, because it's not
1228-
* transactional. Also take a lower lock if no option at all is present.
1229-
*/
1230-
staticLOCKMODE
1231-
alter_sequence_get_lock_level(List*options)
1232-
{
1233-
ListCell*option;
1234-
1235-
foreach(option,options)
1236-
{
1237-
DefElem*defel= (DefElem*)lfirst(option);
1238-
1239-
if (strcmp(defel->defname,"restart")!=0)
1240-
returnShareRowExclusiveLock;
1241-
}
1242-
1243-
returnRowExclusiveLock;
1244-
}
1245-
12461204
/*
12471205
* init_params: process the options list of CREATE or ALTER SEQUENCE, and
12481206
* store the values into appropriate fields of seqform, for changes that go
@@ -1258,7 +1216,6 @@ static void
12581216
init_params(ParseState*pstate,List*options,boolfor_identity,
12591217
boolisInit,
12601218
Form_pg_sequenceseqform,
1261-
bool*changed_seqform,
12621219
Form_pg_sequence_dataseqdataform,
12631220
List**owned_by)
12641221
{
@@ -1378,8 +1335,6 @@ init_params(ParseState *pstate, List *options, bool for_identity,
13781335
defel->defname);
13791336
}
13801337

1381-
*changed_seqform= false;
1382-
13831338
/*
13841339
* We must reset log_cnt when isInit or when changing any parameters that
13851340
* would affect future nextval allocations.
@@ -1420,19 +1375,16 @@ init_params(ParseState *pstate, List *options, bool for_identity,
14201375
}
14211376

14221377
seqform->seqtypid=newtypid;
1423-
*changed_seqform= true;
14241378
}
14251379
elseif (isInit)
14261380
{
14271381
seqform->seqtypid=INT8OID;
1428-
*changed_seqform= true;
14291382
}
14301383

14311384
/* INCREMENT BY */
14321385
if (increment_by!=NULL)
14331386
{
14341387
seqform->seqincrement=defGetInt64(increment_by);
1435-
*changed_seqform= true;
14361388
if (seqform->seqincrement==0)
14371389
ereport(ERROR,
14381390
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
@@ -1442,28 +1394,24 @@ init_params(ParseState *pstate, List *options, bool for_identity,
14421394
elseif (isInit)
14431395
{
14441396
seqform->seqincrement=1;
1445-
*changed_seqform= true;
14461397
}
14471398

14481399
/* CYCLE */
14491400
if (is_cycled!=NULL)
14501401
{
14511402
seqform->seqcycle=intVal(is_cycled->arg);
1452-
*changed_seqform= true;
14531403
Assert(BoolIsValid(seqform->seqcycle));
14541404
seqdataform->log_cnt=0;
14551405
}
14561406
elseif (isInit)
14571407
{
14581408
seqform->seqcycle= false;
1459-
*changed_seqform= true;
14601409
}
14611410

14621411
/* MAXVALUE (null arg means NO MAXVALUE) */
14631412
if (max_value!=NULL&&max_value->arg)
14641413
{
14651414
seqform->seqmax=defGetInt64(max_value);
1466-
*changed_seqform= true;
14671415
seqdataform->log_cnt=0;
14681416
}
14691417
elseif (isInit||max_value!=NULL||reset_max_value)
@@ -1480,7 +1428,6 @@ init_params(ParseState *pstate, List *options, bool for_identity,
14801428
}
14811429
else
14821430
seqform->seqmax=-1;/* descending seq */
1483-
*changed_seqform= true;
14841431
seqdataform->log_cnt=0;
14851432
}
14861433

@@ -1502,7 +1449,6 @@ init_params(ParseState *pstate, List *options, bool for_identity,
15021449
if (min_value!=NULL&&min_value->arg)
15031450
{
15041451
seqform->seqmin=defGetInt64(min_value);
1505-
*changed_seqform= true;
15061452
seqdataform->log_cnt=0;
15071453
}
15081454
elseif (isInit||min_value!=NULL||reset_min_value)
@@ -1519,7 +1465,6 @@ init_params(ParseState *pstate, List *options, bool for_identity,
15191465
}
15201466
else
15211467
seqform->seqmin=1;/* ascending seq */
1522-
*changed_seqform= true;
15231468
seqdataform->log_cnt=0;
15241469
}
15251470

@@ -1555,15 +1500,13 @@ init_params(ParseState *pstate, List *options, bool for_identity,
15551500
if (start_value!=NULL)
15561501
{
15571502
seqform->seqstart=defGetInt64(start_value);
1558-
*changed_seqform= true;
15591503
}
15601504
elseif (isInit)
15611505
{
15621506
if (seqform->seqincrement>0)
15631507
seqform->seqstart=seqform->seqmin;/* ascending seq */
15641508
else
15651509
seqform->seqstart=seqform->seqmax;/* descending seq */
1566-
*changed_seqform= true;
15671510
}
15681511

15691512
/* crosscheck START */
@@ -1638,7 +1581,6 @@ init_params(ParseState *pstate, List *options, bool for_identity,
16381581
if (cache_value!=NULL)
16391582
{
16401583
seqform->seqcache=defGetInt64(cache_value);
1641-
*changed_seqform= true;
16421584
if (seqform->seqcache <=0)
16431585
{
16441586
charbuf[100];
@@ -1654,7 +1596,6 @@ init_params(ParseState *pstate, List *options, bool for_identity,
16541596
elseif (isInit)
16551597
{
16561598
seqform->seqcache=1;
1657-
*changed_seqform= true;
16581599
}
16591600
}
16601601

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