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Commit742cd87

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Ensure that if the OID counter wraps around, we will not generate 0,
nor any OID in the reserved range (1-16383).
1 parent667d5ed commit742cd87

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1 file changed

+83
-91
lines changed

1 file changed

+83
-91
lines changed

‎src/backend/access/transam/varsup.c

Lines changed: 83 additions & 91 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.28 2000/04/12 17:14:53 momjian Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.29 2000/07/25 20:18:19 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -22,16 +22,21 @@
2222
staticvoidGetNewObjectIdBlock(Oid*oid_return,intoid_block_size);
2323
staticvoidVariableRelationGetNextOid(Oid*oid_return);
2424
staticvoidVariableRelationGetNextXid(TransactionId*xidP);
25-
staticvoidVariableRelationPutNextOid(Oid*oidP);
25+
staticvoidVariableRelationPutNextOid(Oidoid);
2626

2727
/* ---------------------
2828
*spin lock for oid generation
2929
* ---------------------
3030
*/
3131
intOidGenLockId;
3232

33+
/* ---------------------
34+
*pointer to "variable cache" in shared memory (set up by shmem.c)
35+
* ---------------------
36+
*/
3337
VariableCacheShmemVariableCache=NULL;
3438

39+
3540
/* ----------------------------------------------------------------
3641
* variable relation query/update routines
3742
* ----------------------------------------------------------------
@@ -48,7 +53,7 @@ VariableRelationGetNextXid(TransactionId *xidP)
4853
VariableRelationContentsvar;
4954

5055
/* ----------------
51-
* We assume that a spinlock has beenacquire to guarantee
56+
* We assume that a spinlock has beenacquired to guarantee
5257
* exclusive access to the variable relation.
5358
* ----------------
5459
*/
@@ -76,6 +81,7 @@ VariableRelationGetNextXid(TransactionId *xidP)
7681
var= (VariableRelationContents)BufferGetBlock(buf);
7782

7883
TransactionIdStore(var->nextXidData,xidP);
84+
7985
ReleaseBuffer(buf);
8086
}
8187

@@ -90,7 +96,7 @@ VariableRelationPutNextXid(TransactionId xid)
9096
VariableRelationContentsvar;
9197

9298
/* ----------------
93-
* We assume that a spinlock has beenacquire to guarantee
99+
* We assume that a spinlock has beenacquired to guarantee
94100
* exclusive access to the variable relation.
95101
* ----------------
96102
*/
@@ -133,22 +139,20 @@ VariableRelationGetNextOid(Oid *oid_return)
133139
VariableRelationContentsvar;
134140

135141
/* ----------------
136-
* We assume that a spinlock has beenacquire to guarantee
142+
* We assume that a spinlock has beenacquired to guarantee
137143
* exclusive access to the variable relation.
138144
* ----------------
139145
*/
140146

141147
/* ----------------
142148
*if the variable relation is not initialized, then we
143149
*assume we are running at bootstrap time and so we return
144-
*an invalid object id -- during this time GetNextBootstrapObjectId
145-
*should be called instead..
150+
*an invalid object id (this path should never be taken, probably).
146151
* ----------------
147152
*/
148153
if (!RelationIsValid(VariableRelation))
149154
{
150-
if (PointerIsValid(oid_return))
151-
(*oid_return)=InvalidOid;
155+
(*oid_return)=InvalidOid;
152156
return;
153157
}
154158

@@ -162,32 +166,12 @@ VariableRelationGetNextOid(Oid *oid_return)
162166
if (!BufferIsValid(buf))
163167
{
164168
SpinRelease(OidGenLockId);
165-
elog(ERROR,"VariableRelationGetNextXid: ReadBuffer failed");
169+
elog(ERROR,"VariableRelationGetNextOid: ReadBuffer failed");
166170
}
167171

168172
var= (VariableRelationContents)BufferGetBlock(buf);
169173

170-
if (PointerIsValid(oid_return))
171-
{
172-
173-
/* ----------------
174-
* nothing up my sleeve...what's going on here is that this code
175-
* is guaranteed never to be called until all files in data/base/
176-
* are created, and the template database exists. at that point,
177-
* we want to append a pg_database tuple. the first time we do
178-
* this, the oid stored in pg_variable will be bogus, so we use
179-
* a bootstrap value defined at the top of this file.
180-
*
181-
* this comment no longer holds true. This code is called before
182-
* all of the files in data/base are created and you can't rely
183-
* on system oid's to be less than BootstrapObjectIdData. mer 9/18/91
184-
* ----------------
185-
*/
186-
if (OidIsValid(var->nextOid))
187-
(*oid_return)=var->nextOid;
188-
else
189-
(*oid_return)=BootstrapObjectIdData;
190-
}
174+
(*oid_return)=var->nextOid;
191175

192176
ReleaseBuffer(buf);
193177
}
@@ -197,13 +181,13 @@ VariableRelationGetNextOid(Oid *oid_return)
197181
* --------------------------------
198182
*/
199183
staticvoid
200-
VariableRelationPutNextOid(Oid*oidP)
184+
VariableRelationPutNextOid(Oidoid)
201185
{
202186
Bufferbuf;
203187
VariableRelationContentsvar;
204188

205189
/* ----------------
206-
* We assume that a spinlock has beenacquire to guarantee
190+
* We assume that a spinlock has beenacquired to guarantee
207191
* exclusive access to the variable relation.
208192
* ----------------
209193
*/
@@ -215,16 +199,6 @@ VariableRelationPutNextOid(Oid *oidP)
215199
if (!RelationIsValid(VariableRelation))
216200
return;
217201

218-
/* ----------------
219-
*sanity check
220-
* ----------------
221-
*/
222-
if (!PointerIsValid(oidP))
223-
{
224-
SpinRelease(OidGenLockId);
225-
elog(ERROR,"VariableRelationPutNextOid: invalid oid pointer");
226-
}
227-
228202
/* ----------------
229203
*read the variable page, update the nextXid field and
230204
*write the page back out to disk.
@@ -240,7 +214,7 @@ VariableRelationPutNextOid(Oid *oidP)
240214

241215
var= (VariableRelationContents)BufferGetBlock(buf);
242216

243-
var->nextOid=(*oidP);
217+
var->nextOid=oid;
244218

245219
WriteBuffer(buf);
246220
}
@@ -253,20 +227,20 @@ VariableRelationPutNextOid(Oid *oidP)
253227
/* ----------------
254228
*GetNewTransactionId
255229
*
256-
*In the version 2 transaction system, transaction id's are
257-
*restricted in several ways.
258-
*
259-
*-- Old comments removed
230+
*Transaction IDs are allocated via a cache in shared memory.
231+
*Each time we need more IDs, we advance the "next XID" value
232+
*in pg_variable by VAR_XID_PREFETCH and set the cache to
233+
*show that many XIDs as available. Then, allocating those XIDs
234+
*requires just a spinlock and not a buffer read/write cycle.
260235
*
261-
*Second, since we may someday preform compression of the data
262-
*in the log and time relations, we cause the numbering of the
263-
*transaction ids to begin at 512. This means that some space
264-
*on the page of the log and time relations corresponding to
265-
*transaction id's 0 - 510 will never be used. This space is
266-
*in fact used to store the version number of the postgres
267-
*transaction log and will someday store compression information
268-
*about the log.-- this is also old comments...
236+
*Since the cache is shared across all backends, cached but unused
237+
*XIDs are not lost when a backend exits, only when the postmaster
238+
*quits or forces shared memory reinit. So we can afford to have
239+
*a pretty big value of VAR_XID_PREFETCH.
269240
*
241+
*This code does not worry about initializing the transaction counter
242+
*(see transam.c's InitializeTransactionLog() for that). We also
243+
*ignore the possibility that the counter could someday wrap around.
270244
* ----------------
271245
*/
272246

@@ -352,44 +326,65 @@ ReadNewTransactionId(TransactionId *xid)
352326
*GetNewObjectIdBlock
353327
*
354328
*This support function is used to allocate a block of object ids
355-
*of the given size.applications wishing to do their own object
356-
*id assignments should use this
329+
*of the given size.
357330
* ----------------
358331
*/
359332
staticvoid
360-
GetNewObjectIdBlock(Oid*oid_return,/* place to return thenew object
361-
* id */
333+
GetNewObjectIdBlock(Oid*oid_return,/* place to return thefirst new
334+
*objectid */
362335
intoid_block_size)/* number of oids desired */
363336
{
337+
Oidfirstfreeoid;
364338
Oidnextoid;
365339

366340
/* ----------------
367-
*SOMEDAY obtain exclusive access to the variable relation page
368-
*That someday is today -mer 6 Aug 1992
341+
* Obtain exclusive access to the variable relation page
369342
* ----------------
370343
*/
371344
SpinAcquire(OidGenLockId);
372345

373346
/* ----------------
374347
*get the "next" oid from the variable relation
375-
*and give it to the caller.
376348
* ----------------
377349
*/
378-
VariableRelationGetNextOid(&nextoid);
379-
if (PointerIsValid(oid_return))
380-
(*oid_return)=nextoid;
350+
VariableRelationGetNextOid(&firstfreeoid);
351+
352+
/* ----------------
353+
*Allocate the range of OIDs to be returned to the caller.
354+
*
355+
*There are two things going on here.
356+
*
357+
*One: in a virgin database pg_variable will initially contain zeroes,
358+
*so we will read out firstfreeoid = InvalidOid. We want to start
359+
*allocating OIDs at BootstrapObjectIdData instead (OIDs below that
360+
*are reserved for static assignment in the initial catalog data).
361+
*
362+
*Two: if a database is run long enough, the OID counter will wrap
363+
*around. We must not generate an invalid OID when that happens,
364+
*and it seems wise not to generate anything in the reserved range.
365+
*Therefore we advance to BootstrapObjectIdData in this case too.
366+
*
367+
*The comparison here assumes that Oid is an unsigned type.
368+
*/
369+
nextoid=firstfreeoid+oid_block_size;
370+
371+
if (!OidIsValid(firstfreeoid)||nextoid<firstfreeoid)
372+
{
373+
/* Initialization or wraparound time, force it up to safe range */
374+
firstfreeoid=BootstrapObjectIdData;
375+
nextoid=firstfreeoid+oid_block_size;
376+
}
377+
378+
(*oid_return)=firstfreeoid;
381379

382380
/* ----------------
383-
*now increment the variable relation's next oid
384-
*field by the size of the oid block requested.
381+
*Update the variable relation to show the block range as used.
385382
* ----------------
386383
*/
387-
nextoid+=oid_block_size;
388-
VariableRelationPutNextOid(&nextoid);
384+
VariableRelationPutNextOid(nextoid);
389385

390386
/* ----------------
391-
*SOMEDAY relinquish our lock on the variable relation page
392-
*That someday is today -mer 6 Apr 1992
387+
*Relinquish our lock on the variable relation page
393388
* ----------------
394389
*/
395390
SpinRelease(OidGenLockId);
@@ -406,9 +401,14 @@ GetNewObjectIdBlock(Oid *oid_return,/* place to return the new object
406401
*relation by 32 for each backend.
407402
*
408403
*Note: 32 has no special significance.We don't want the
409-
* number to be too large becauseifwhen the backend
404+
* number to be too large because when the backend
410405
* terminates, we lose the oids we cached.
411406
*
407+
*Question: couldn't we use a shared-memory cache just like XIDs?
408+
*That would allow a larger interval between pg_variable updates
409+
*without cache losses. Note, however, that we can assign an OID
410+
*without even a spinlock from the backend-local OID cache.
411+
*Maybe two levels of caching would be good.
412412
* ----------------
413413
*/
414414

@@ -431,11 +431,7 @@ GetNewObjectId(Oid *oid_return) /* place to return the new object id */
431431
intoid_block_size=VAR_OID_PREFETCH;
432432

433433
/* ----------------
434-
*during bootstrap time, we want to allocate oids
435-
*one at a time.Otherwise there might be some
436-
*bootstrap oid's left in the block we prefetch which
437-
*would be passed out after the variable relation was
438-
*initialized. This would be bad.
434+
*Make sure pg_variable is open.
439435
* ----------------
440436
*/
441437
if (!RelationIsValid(VariableRelation))
@@ -469,12 +465,11 @@ GetNewObjectId(Oid *oid_return) /* place to return the new object id */
469465
void
470466
CheckMaxObjectId(Oidassigned_oid)
471467
{
472-
Oidpass_oid;
473-
468+
Oidtemp_oid;
474469

475470
if (prefetched_oid_count==0)/* make sure next/max is set, or
476471
* reload */
477-
GetNewObjectId(&pass_oid);
472+
GetNewObjectId(&temp_oid);
478473

479474
/* ----------------
480475
*If we are below prefetched limits, do nothing
@@ -488,7 +483,6 @@ CheckMaxObjectId(Oid assigned_oid)
488483
*If we are here, we are coming from a 'copy from' with oid's
489484
*
490485
*If we are in the prefetched oid range, just bump it up
491-
*
492486
* ----------------
493487
*/
494488

@@ -506,21 +500,19 @@ CheckMaxObjectId(Oid assigned_oid)
506500
*but we are loading oid's that we can not guarantee are unique
507501
*anyway, so we must rely on the user
508502
*
509-
*
510503
* We now:
511504
* set the variable relation with the new max oid
512505
* force the backend to reload its oid cache
513506
*
514-
* We use the oid cache so we don't have to update the variable
515-
* relation every time
516-
*
507+
* By reloading the oid cache, we don't have to update the variable
508+
* relation every time when sequential OIDs are being loaded by COPY.
517509
* ----------------
518510
*/
519511

520-
pass_oid=assigned_oid;
521-
VariableRelationPutNextOid(&pass_oid);/* not modified */
522-
prefetched_oid_count=0;/* force reload */
523-
pass_oid=assigned_oid;
524-
GetNewObjectId(&pass_oid);/* throw away returned oid */
512+
SpinAcquire(OidGenLockId);
513+
VariableRelationPutNextOid(assigned_oid);
514+
SpinRelease(OidGenLockId);
525515

516+
prefetched_oid_count=0;/* force reload */
517+
GetNewObjectId(&temp_oid);/* cause target OID to be allocated */
526518
}

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