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Commitaa64f23

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Remove MaxBackends variable in favor of GetMaxBackends() function.
Previously, it was really easy to write code that accessed MaxBackendsbefore we'd actually initialized it, especially when coding up anextension. To make this less error-prune, introduce a new functionGetMaxBackends() which should be used to obtain the correct value.This will ERROR if called too early. Demote the global variable toa file-level static, so that nobody can peak at it directly.Nathan Bossart. Idea by Andres Freund. Review by Greg Sabino Mullane,by Michael Paquier (who had doubts about the approach), and by me.Discussion:http://postgr.es/m/20210802224204.bckcikl45uezv5e4@alap3.anarazel.de
1 parent2da8961 commitaa64f23

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19 files changed

+218
-133
lines changed

19 files changed

+218
-133
lines changed

‎src/backend/access/nbtree/nbtutils.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -2072,7 +2072,7 @@ BTreeShmemSize(void)
20722072
Sizesize;
20732073

20742074
size= offsetof(BTVacInfo,vacuums);
2075-
size=add_size(size,mul_size(MaxBackends,sizeof(BTOneVacInfo)));
2075+
size=add_size(size,mul_size(GetMaxBackends(),sizeof(BTOneVacInfo)));
20762076
returnsize;
20772077
}
20782078

@@ -2101,7 +2101,7 @@ BTreeShmemInit(void)
21012101
btvacinfo->cycle_ctr= (BTCycleId)time(NULL);
21022102

21032103
btvacinfo->num_vacuums=0;
2104-
btvacinfo->max_vacuums=MaxBackends;
2104+
btvacinfo->max_vacuums=GetMaxBackends();
21052105
}
21062106
else
21072107
Assert(found);

‎src/backend/access/transam/multixact.c

Lines changed: 22 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -282,12 +282,11 @@ typedef struct MultiXactStateData
282282
}MultiXactStateData;
283283

284284
/*
285-
* Last element of OldestMemberMXactId and OldestVisibleMXactId arrays.
286-
* Valid elements are (1..MaxOldestSlot); element 0 is never used.
285+
* Pointers to the state data in shared memory
286+
*
287+
* The index of the last element of the OldestMemberMXactId and
288+
* OldestVisibleMXacId arrays can be obtained with GetMaxOldestSlot().
287289
*/
288-
#defineMaxOldestSlot(MaxBackends + max_prepared_xacts)
289-
290-
/* Pointers to the state data in shared memory */
291290
staticMultiXactStateData*MultiXactState;
292291
staticMultiXactId*OldestMemberMXactId;
293292
staticMultiXactId*OldestVisibleMXactId;
@@ -342,6 +341,7 @@ static void MultiXactIdSetOldestVisible(void);
342341
staticvoidRecordNewMultiXact(MultiXactIdmulti,MultiXactOffsetoffset,
343342
intnmembers,MultiXactMember*members);
344343
staticMultiXactIdGetNewMultiXactId(intnmembers,MultiXactOffset*offset);
344+
staticinlineintGetMaxOldestSlot(void);
345345

346346
/* MultiXact cache management */
347347
staticintmxactMemberComparator(constvoid*arg1,constvoid*arg2);
@@ -662,6 +662,17 @@ MultiXactIdSetOldestMember(void)
662662
}
663663
}
664664

665+
/*
666+
* Retrieve the index of the last element of the OldestMemberMXactId and
667+
* OldestVisibleMXactId arrays. Valid elements are (1..MaxOldestSlot); element
668+
* 0 is never used.
669+
*/
670+
staticinlineint
671+
GetMaxOldestSlot(void)
672+
{
673+
returnGetMaxBackends()+max_prepared_xacts;
674+
}
675+
665676
/*
666677
* MultiXactIdSetOldestVisible
667678
*Save the oldest MultiXactId this transaction considers possibly live.
@@ -684,6 +695,7 @@ MultiXactIdSetOldestVisible(void)
684695
if (!MultiXactIdIsValid(OldestVisibleMXactId[MyBackendId]))
685696
{
686697
MultiXactIdoldestMXact;
698+
intmaxOldestSlot=GetMaxOldestSlot();
687699
inti;
688700

689701
LWLockAcquire(MultiXactGenLock,LW_EXCLUSIVE);
@@ -697,7 +709,7 @@ MultiXactIdSetOldestVisible(void)
697709
if (oldestMXact<FirstMultiXactId)
698710
oldestMXact=FirstMultiXactId;
699711

700-
for (i=1;i <=MaxOldestSlot;i++)
712+
for (i=1;i <=maxOldestSlot;i++)
701713
{
702714
MultiXactIdthisoldest=OldestMemberMXactId[i];
703715

@@ -1831,7 +1843,7 @@ MultiXactShmemSize(void)
18311843
/* We need 2*MaxOldestSlot + 1 perBackendXactIds[] entries */
18321844
#defineSHARED_MULTIXACT_STATE_SIZE \
18331845
add_size(offsetof(MultiXactStateData, perBackendXactIds) + sizeof(MultiXactId), \
1834-
mul_size(sizeof(MultiXactId) * 2,MaxOldestSlot))
1846+
mul_size(sizeof(MultiXactId) * 2,GetMaxOldestSlot()))
18351847

18361848
size=SHARED_MULTIXACT_STATE_SIZE;
18371849
size=add_size(size,SimpleLruShmemSize(NUM_MULTIXACTOFFSET_BUFFERS,0));
@@ -1882,7 +1894,7 @@ MultiXactShmemInit(void)
18821894
* since we only use indexes 1..MaxOldestSlot in each array.
18831895
*/
18841896
OldestMemberMXactId=MultiXactState->perBackendXactIds;
1885-
OldestVisibleMXactId=OldestMemberMXactId+MaxOldestSlot;
1897+
OldestVisibleMXactId=OldestMemberMXactId+GetMaxOldestSlot();
18861898
}
18871899

18881900
/*
@@ -2507,6 +2519,7 @@ GetOldestMultiXactId(void)
25072519
{
25082520
MultiXactIdoldestMXact;
25092521
MultiXactIdnextMXact;
2522+
intmaxOldestSlot=GetMaxOldestSlot();
25102523
inti;
25112524

25122525
/*
@@ -2525,7 +2538,7 @@ GetOldestMultiXactId(void)
25252538
nextMXact=FirstMultiXactId;
25262539

25272540
oldestMXact=nextMXact;
2528-
for (i=1;i <=MaxOldestSlot;i++)
2541+
for (i=1;i <=maxOldestSlot;i++)
25292542
{
25302543
MultiXactIdthisoldest;
25312544

‎src/backend/access/transam/twophase.c

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -260,6 +260,7 @@ TwoPhaseShmemInit(void)
260260
{
261261
GlobalTransactiongxacts;
262262
inti;
263+
intmax_backends=GetMaxBackends();
263264

264265
Assert(!found);
265266
TwoPhaseState->freeGXacts=NULL;
@@ -293,7 +294,7 @@ TwoPhaseShmemInit(void)
293294
* prepared transaction. Currently multixact.c uses that
294295
* technique.
295296
*/
296-
gxacts[i].dummyBackendId=MaxBackends+1+i;
297+
gxacts[i].dummyBackendId=max_backends+1+i;
297298
}
298299
}
299300
else

‎src/backend/commands/async.c

Lines changed: 6 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -518,7 +518,7 @@ AsyncShmemSize(void)
518518
Sizesize;
519519

520520
/* This had better match AsyncShmemInit */
521-
size=mul_size(MaxBackends+1,sizeof(QueueBackendStatus));
521+
size=mul_size(GetMaxBackends()+1,sizeof(QueueBackendStatus));
522522
size=add_size(size, offsetof(AsyncQueueControl,backend));
523523

524524
size=add_size(size,SimpleLruShmemSize(NUM_NOTIFY_BUFFERS,0));
@@ -534,14 +534,15 @@ AsyncShmemInit(void)
534534
{
535535
boolfound;
536536
Sizesize;
537+
intmax_backends=GetMaxBackends();
537538

538539
/*
539540
* Create or attach to the AsyncQueueControl structure.
540541
*
541542
* The used entries in the backend[] array run from 1 to MaxBackends; the
542543
* zero'th entry is unused but must be allocated.
543544
*/
544-
size=mul_size(MaxBackends+1,sizeof(QueueBackendStatus));
545+
size=mul_size(max_backends+1,sizeof(QueueBackendStatus));
545546
size=add_size(size, offsetof(AsyncQueueControl,backend));
546547

547548
asyncQueueControl= (AsyncQueueControl*)
@@ -556,7 +557,7 @@ AsyncShmemInit(void)
556557
QUEUE_FIRST_LISTENER=InvalidBackendId;
557558
asyncQueueControl->lastQueueFillWarn=0;
558559
/* zero'th entry won't be used, but let's initialize it anyway */
559-
for (inti=0;i <=MaxBackends;i++)
560+
for (inti=0;i <=max_backends;i++)
560561
{
561562
QUEUE_BACKEND_PID(i)=InvalidPid;
562563
QUEUE_BACKEND_DBOID(i)=InvalidOid;
@@ -1641,8 +1642,8 @@ SignalBackends(void)
16411642
* XXX in principle these pallocs could fail, which would be bad. Maybe
16421643
* preallocate the arrays? They're not that large, though.
16431644
*/
1644-
pids= (int32*)palloc(MaxBackends*sizeof(int32));
1645-
ids= (BackendId*)palloc(MaxBackends*sizeof(BackendId));
1645+
pids= (int32*)palloc(GetMaxBackends()*sizeof(int32));
1646+
ids= (BackendId*)palloc(GetMaxBackends()*sizeof(BackendId));
16461647
count=0;
16471648

16481649
LWLockAcquire(NotifyQueueLock,LW_EXCLUSIVE);

‎src/backend/libpq/pqcomm.c

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -349,6 +349,7 @@ StreamServerPort(int family, const char *hostName, unsigned short portNumber,
349349
structaddrinfohint;
350350
intlisten_index=0;
351351
intadded=0;
352+
intmax_backends=GetMaxBackends();
352353

353354
#ifdefHAVE_UNIX_SOCKETS
354355
charunixSocketPath[MAXPGPATH];
@@ -571,7 +572,7 @@ StreamServerPort(int family, const char *hostName, unsigned short portNumber,
571572
* intended to provide a clamp on the request on platforms where an
572573
* overly large request provokes a kernel error (are there any?).
573574
*/
574-
maxconn=MaxBackends*2;
575+
maxconn=max_backends*2;
575576
if (maxconn>PG_SOMAXCONN)
576577
maxconn=PG_SOMAXCONN;
577578

‎src/backend/postmaster/auxprocess.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -116,7 +116,7 @@ AuxiliaryProcessMain(AuxProcType auxtype)
116116
* This will need rethinking if we ever want more than one of a particular
117117
* auxiliary process type.
118118
*/
119-
ProcSignalInit(MaxBackends+MyAuxProcType+1);
119+
ProcSignalInit(GetMaxBackends()+MyAuxProcType+1);
120120

121121
/*
122122
* Auxiliary processes don't run transactions, but they may need a

‎src/backend/postmaster/postmaster.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -6260,7 +6260,7 @@ save_backend_variables(BackendParameters *param, Port *port,
62606260
param->query_id_enabled=query_id_enabled;
62616261
param->max_safe_fds=max_safe_fds;
62626262

6263-
param->MaxBackends=MaxBackends;
6263+
param->MaxBackends=GetMaxBackends();
62646264

62656265
#ifdefWIN32
62666266
param->PostmasterHandle=PostmasterHandle;
@@ -6494,7 +6494,7 @@ restore_backend_variables(BackendParameters *param, Port *port)
64946494
query_id_enabled=param->query_id_enabled;
64956495
max_safe_fds=param->max_safe_fds;
64966496

6497-
MaxBackends=param->MaxBackends;
6497+
SetMaxBackends(param->MaxBackends);
64986498

64996499
#ifdefWIN32
65006500
PostmasterHandle=param->PostmasterHandle;

‎src/backend/storage/ipc/dsm.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -166,7 +166,7 @@ dsm_postmaster_startup(PGShmemHeader *shim)
166166

167167
/* Determine size for new control segment. */
168168
maxitems=PG_DYNSHMEM_FIXED_SLOTS
169-
+PG_DYNSHMEM_SLOTS_PER_BACKEND*MaxBackends;
169+
+PG_DYNSHMEM_SLOTS_PER_BACKEND*GetMaxBackends();
170170
elog(DEBUG2,"dynamic shared memory system will support %u segments",
171171
maxitems);
172172
segsize=dsm_control_bytes_needed(maxitems);

‎src/backend/storage/ipc/procarray.c

Lines changed: 17 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -97,7 +97,7 @@ typedef struct ProcArrayStruct
9797
/* oldest catalog xmin of any replication slot */
9898
TransactionIdreplication_slot_catalog_xmin;
9999

100-
/* indexes into allProcs[], hasPROCARRAY_MAXPROCS entries */
100+
/* indexes into allProcs[], hasProcArrayMaxProcs entries */
101101
intpgprocnos[FLEXIBLE_ARRAY_MEMBER];
102102
}ProcArrayStruct;
103103

@@ -355,6 +355,17 @@ static void MaintainLatestCompletedXidRecovery(TransactionId latestXid);
355355
staticinlineFullTransactionIdFullXidRelativeTo(FullTransactionIdrel,
356356
TransactionIdxid);
357357
staticvoidGlobalVisUpdateApply(ComputeXidHorizonsResult*horizons);
358+
staticinlineintGetProcArrayMaxProcs(void);
359+
360+
361+
/*
362+
* Retrieve the number of slots in the ProcArray structure.
363+
*/
364+
staticinlineint
365+
GetProcArrayMaxProcs(void)
366+
{
367+
returnGetMaxBackends()+max_prepared_xacts;
368+
}
358369

359370
/*
360371
* Report shared-memory space needed by CreateSharedProcArray.
@@ -365,10 +376,8 @@ ProcArrayShmemSize(void)
365376
Sizesize;
366377

367378
/* Size of the ProcArray structure itself */
368-
#definePROCARRAY_MAXPROCS(MaxBackends + max_prepared_xacts)
369-
370379
size= offsetof(ProcArrayStruct,pgprocnos);
371-
size=add_size(size,mul_size(sizeof(int),PROCARRAY_MAXPROCS));
380+
size=add_size(size,mul_size(sizeof(int),GetProcArrayMaxProcs()));
372381

373382
/*
374383
* During Hot Standby processing we have a data structure called
@@ -384,7 +393,7 @@ ProcArrayShmemSize(void)
384393
* shared memory is being set up.
385394
*/
386395
#defineTOTAL_MAX_CACHED_SUBXIDS \
387-
((PGPROC_MAX_CACHED_SUBXIDS + 1) *PROCARRAY_MAXPROCS)
396+
((PGPROC_MAX_CACHED_SUBXIDS + 1) *GetProcArrayMaxProcs())
388397

389398
if (EnableHotStandby)
390399
{
@@ -411,7 +420,7 @@ CreateSharedProcArray(void)
411420
ShmemInitStruct("Proc Array",
412421
add_size(offsetof(ProcArrayStruct,pgprocnos),
413422
mul_size(sizeof(int),
414-
PROCARRAY_MAXPROCS)),
423+
GetProcArrayMaxProcs())),
415424
&found);
416425

417426
if (!found)
@@ -420,7 +429,7 @@ CreateSharedProcArray(void)
420429
* We're the first - initialize.
421430
*/
422431
procArray->numProcs=0;
423-
procArray->maxProcs=PROCARRAY_MAXPROCS;
432+
procArray->maxProcs=GetProcArrayMaxProcs();
424433
procArray->maxKnownAssignedXids=TOTAL_MAX_CACHED_SUBXIDS;
425434
procArray->numKnownAssignedXids=0;
426435
procArray->tailKnownAssignedXids=0;
@@ -4623,7 +4632,7 @@ KnownAssignedXidsCompress(bool force)
46234632
*/
46244633
intnelements=head-tail;
46254634

4626-
if (nelements<4*PROCARRAY_MAXPROCS||
4635+
if (nelements<4*GetProcArrayMaxProcs()||
46274636
nelements<2*pArray->numKnownAssignedXids)
46284637
return;
46294638
}

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