8000 Fix memory leak and other bugs in ginPlaceToPage() & subroutines. · prmdeveloper/postgres@ef35afa · GitHub
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Fix memory leak and other bugs in ginPlaceToPage() & subroutines.
Commit 36a35c5 turned the interface between ginPlaceToPage and its subroutines in gindatapage.c and ginentrypage.c into a royal mess: page-update critical sections were started in one place and finished in another place not even in the same file, and the very same subroutine might return having started a critical section or not. Subsequent patches band-aided over some of the problems with this design by making things even messier. One user-visible resulting problem is memory leaks caused by the need for the subroutines to allocate storage that would survive until ginPlaceToPage calls XLogInsert (as reported by Julien Rouhaud). This would not typically be noticeable during retail index updates. It could be visible in a GIN index build, in the form of memory consumption swelling to several times the commanded maintenance_work_mem. Another rather nasty problem is that in the internal-page-splitting code path, we would clear the child page's GIN_INCOMPLETE_SPLIT flag well before entering the critical section that it's supposed to be cleared in; a failure in between would leave the index in a corrupt state. There were also assorted coding-rule violations with little immediate consequence but possible long-term hazards, such as beginning an XLogInsert sequence before entering a critical section, or calling elog(DEBUG) inside a critical section. To fix, redefine the API between ginPlaceToPage() and its subroutines by splitting the subroutines into two parts. The "beginPlaceToPage" subroutine does what can be done outside a critical section, including full computation of the result pages into temporary storage when we're going to split the target page. The "execPlaceToPage" subroutine is called within a critical section established by ginPlaceToPage(), and it handles the actual page update in the non-split code path. The critical section, as well as the XLOG insertion call sequence, are both now always started and finished in ginPlaceToPage(). Also, make ginPlaceToPage() create and work in a short-lived memory context to eliminate the leakage problem. (Since a short-lived memory context had been getting created in the most common code path in the subroutines, this shouldn't cause any noticeable performance penalty; we're just moving the overhead up one call level.) In passing, fix a bunch of comments that had gone unmaintained throughout all this klugery. Report: <571276DD.5050303@dalibo.com>
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‎src/backend/access/gin/ginbtree.c‎

Lines changed: 119 additions & 84 deletions
Original file line numberDiff line numberDiff line change
@@ -16,6 +16,7 @@
1616

1717
#include "access/gin_private.h"
1818
#include "miscadmin.h"
19+
#include "utils/memutils.h"
1920
#include "utils/rel.h"
2021

2122
static void ginFindParents(GinBtree btree, GinBtreeStack *stack);
@@ -309,28 +310,46 @@ ginFindParents(GinBtree btree, GinBtreeStack *stack)
309310
* Insert a new item to a page.
310311
*
311312
* Returns true if the insertion was finished. On false, the page was split and
312-
* the parent needs to be updated. (a root split returns true as it doesn't
313-
* need any further action by the caller to complete)
313+
* the parent needs to be updated. (A root split returns true as it doesn't
314+
* need any further action by the caller to complete.)
314315
*
315-
* When inserting a downlink to a internal page, 'childbuf' contains the
316+
* When inserting a downlink to an internal page, 'childbuf' contains the
316317
* child page that was split. Its GIN_INCOMPLETE_SPLIT flag will be cleared
317-
* atomically with the insert. Also, the existing item at the given location
318-
* is updated to point to 'updateblkno'.
318+
* atomically with the insert. Also, the existing item at offset stack->off
319+
* in the target page is updated to point to updateblkno.
319320
*
320321
* stack->buffer is locked on entry, and is kept locked.
322+
* Likewise for childbuf, if given.
321323
*/
322324
static bool
323325
ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
324326
void *insertdata, BlockNumber updateblkno,
325327
Buffer childbuf, GinStatsData *buildStats)
326328
{
327329
Page page = BufferGetPage(stack->buffer);
328-
XLogRecData *payloadrdata;
330+
bool result;
329331
GinPlaceToPageRC rc;
330332
uint16 xlflags = 0;
331333
Page childpage = NULL;
332334
Page newlpage = NULL,
333335
newrpage = NULL;
336+
void *ptp_workspace = NULL;
337+
XLogRecData payloadrdata[10];
338+
MemoryContext tmpCxt;
339+
MemoryContext oldCxt;
340+
341+
/*
342+
* We do all the work of this function and its subfunctions in a temporary
343+
* memory context. This avoids leakages and simplifies APIs, since some
344+
* subfunctions allocate storage that has to survive until we've finished
345+
* the WAL insertion.
346+
*/
347+
tmpCxt = AllocSetContextCreate(CurrentMemoryContext,
348+
"ginPlaceToPage temporary context",
349+
ALLOCSET_DEFAULT_MINSIZE,
350+
ALLOCSET_DEFAULT_INITSIZE,
351+
ALLOCSET_DEFAULT_MAXSIZE);
352+
oldCxt = MemoryContextSwitchTo(tmpCxt);
334353

335354
if (GinPageIsData(page))
336355
xlflags |= GIN_INSERT_ISDATA;
@@ -348,21 +367,36 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
348367
}
349368

350369
/*
351-
* Try to put the incoming tuple on the page. placeToPage will decide if
352-
* the page needs to be split.
370+
* See if the incoming tuple will fit on the page. beginPlaceToPage will
371+
* decide if the page needs to be split, and will compute the split
372+
* contents if so. See comments for beginPlaceToPage and execPlaceToPage
373+
* functions for more details of the API here.
353374
*/
354-
rc = btree->placeToPage(btree, stack->buffer, stack,
355-
insertdata, updateblkno,
356-
&payloadrdata, &newlpage, &newrpage);
357-
if (rc == UNMODIFIED)
358-
return true;
359-
else if (rc == INSERTED)
375+
rc = btree->beginPlaceToPage(btree, stack->buffer, stack,
376+
insertdata, updateblkno,
377+
&ptp_workspace,
378+
&newlpage, &newrpage,
379+
payloadrdata);
380+
381+
if (rc == GPTP_NO_WORK)
360382
{
361-
/* placeToPage did START_CRIT_SECTION() */
383+
/* Nothing to do */
384+
result = true;
385+
}
386+
else if (rc == GPTP_INSERT)
387+
{
388+
/* It will fit, perform the insertion */
389+
START_CRIT_SECTION();
390+
391+
/* Perform the page update, and set up WAL data about it */
392+
btree->execPlaceToPage(btree, stack->buffer, stack,
393+
insertdata, updateblkno,
394+
ptp_workspace, payloadrdata);
395+
362396
MarkBufferDirty(stack->buffer);
363397

364398
/* An insert to an internal page finishes the split of the child. */
365-
if (childbuf != InvalidBuffer)
399+
if (BufferIsValid(childbuf))
366400
{
367401
GinPageGetOpaque(childpage)->flags &= ~GIN_INCOMPLETE_SPLIT;
368402
MarkBufferDirty(childbuf);
@@ -387,7 +421,7 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
387421
* Log information about child if this was an insertion of a
388422
* downlink.
389423
*/
390-
if (childbuf != InvalidBuffer)
424+
if (BufferIsValid(childbuf))
391425
{
392426
rdata[0].next = &rdata[1];
393427

@@ -400,7 +434,7 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
400434
rdata[1].next = &rdata[2];
401435

402436
rdata[2].buffer = childbuf;
403-
rdata[2].buffer_std = false;
437+
rdata[2].buffer_std = true;
404438
rdata[2].data = NULL;
405439
rdata[2].len = 0;
406440
rdata[2].next = payloadrdata;
@@ -409,25 +443,31 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
409443
rdata[0].next = payloadrdata;
410444

411445
recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_INSERT, rdata);
446+
412447
PageSetLSN(page, recptr);
413-
if (childbuf != InvalidBuffer)
448+
if (BufferIsValid(childbuf))
414449
PageSetLSN(childpage, recptr);
415450
}
416451

417452
END_CRIT_SECTION();
418453

419-
return true;
454+
/* Insertion is complete. */
455+
result = true;
420456
}
421-
else if (rc == SPLIT)
457+
else if (rc == GPTP_SPLIT)
422458
{
423-
/* Didn't fit, have to split */
459+
/*
460+
* Didn't fit, need to split. The split has been computed in newlpage
461+
* and newrpage, which are pointers to palloc'd pages, not associated
462+
* with buffers. stack->buffer is not touched yet.
463+
*/
424464
Buffer rbuffer;
425465
BlockNumber savedRightLink;
426-
XLogRecData rdata[2];
427466
ginxlogSplit data;
428467
Buffer lbuffer = InvalidBuffer;
429468
Page newrootpg = NULL;
430469

470+
/* Get a new index page to become the right page */
431471
rbuffer = GinNewBuffer(btree->index);
432472

433473
/* During index build, count the new page */
@@ -441,52 +481,27 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
441481

442482
savedRightLink = GinPageGetOpaque(page)->rightlink;
443483

444-
/*
445-
* newlpage and newrpage are pointers to memory pages, not associated
446-
* with buffers. stack->buffer is not touched yet.
447-
*/
448-
484+
/* Begin setting up WAL record (which we might not use) */
449485
data.node = btree->index->rd_node;
450486
data.rblkno = BufferGetBlockNumber(rbuffer);
451487
data.flags = xlflags;
452-
if (childbuf != InvalidBuffer)
488+
if (BufferIsValid(childbuf))
453489
{
454-
Page childpage = BufferGetPage(childbuf);
455-
456-
GinPageGetOpaque(childpage)->flags &= ~GIN_INCOMPLETE_SPLIT;
457-
458490
data.leftChildBlkno = BufferGetBlockNumber(childbuf);
459491
data.rightChildBlkno = GinPageGetOpaque(childpage)->rightlink;
460492
}
461493
else
462494
data.leftChildBlkno = data.rightChildBlkno = InvalidBlockNumber;
463495

464-
rdata[0].buffer = InvalidBuffer;
465-
rdata[0].data = (char *) &data;
466-
rdata[0].len = sizeof(ginxlogSplit);
467-
468-
if (childbuf != InvalidBuffer)
469-
{
470-
rdata[0].next = &rdata[1];
471-
472-
rdata[1].buffer = childbuf;
473-
rdata[1].buffer_std = false;
474-
rdata[1].data = NULL;
475-
rdata[1].len = 0;
476-
rdata[1].next = payloadrdata;
477-
}
478-
else
479-
rdata[0].next = payloadrdata;
480-
481496
if (stack->parent == NULL)
482497
{
483498
/*
484-
* split root, so we need to allocate new left page and place
485-
* pointer on root to left and right page
499+
* splitting the root, so we need to allocate new left page and
500+
* place pointers to left and right page on root page.
486501
*/
487502
lbuffer = GinNewBuffer(btree->index);
488503

489-
/* During index build, count the newly-added root page */
504+
/* During index build, count the new left page */
490505
if (buildStats)
491506
{
492507
if (btree->isData)
@@ -508,9 +523,9 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
508523

509524
/*
510525
* Construct a new root page containing downlinks to the new left
511-
* and right pages. (do this in a temporary copy first rather than
512-
* overwriting the original page directly, so that we can still
513-
* abort gracefully if this fails.)
526+
* and right pages. (Do this in a temporary copy rather than
527+
* overwriting the original page directly, since we're not in the
528+
* critical section yet.)
514529
*/
515530
newrootpg = PageGetTempPage(newrpage);
516531
GinInitPage(newrootpg, GinPageGetOpaque(newlpage)->flags & ~(GIN_LEAF | GIN_COMPRESSED), BLCKSZ);
@@ -521,7 +536,7 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
521536
}
522537
else
523538
{
524-
/* split non-root page */
539+
/* splitting a non-root page */
525540
data.rrlink = savedRightLink;
526541
data.lblkno = BufferGetBlockNumber(stack->buffer);
527542

@@ -531,48 +546,70 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
531546
}
532547

533548
/*
534-
* Ok, we have the new contents of the left page in a temporary copy
535-
* now (newlpage), and the newly-allocated right block has been filled
536-
* in. The original page is still unchanged.
549+
* OK, we have the new contents of the left page in a temporary copy
550+
* now (newlpage), and likewise for the new contents of the
551+
* newly-allocated right block. The original page is still unchanged.
537552
*
538553
* If this is a root split, we also have a temporary page containing
539-
* the new contents of the root. Copy the new left page to a
540-
* newly-allocated block, and initialize the (original) root page the
541-
* new copy. Otherwise, copy over the temporary copy of the new left
542-
* page over the old left page.
554+
* the new contents of the root.
543555
*/
544556

545557
START_CRIT_SECTION();
546558

547559
MarkBufferDirty(rbuffer);
548560
MarkBufferDirty(stack->buffer);
549-
if (BufferIsValid(childbuf))
550-
MarkBufferDirty(childbuf);
551561

552562
/*
553-
* Restore the temporary copies over the real buffers. But don't free
554-
* the temporary copies yet, WAL record data points to them.
563+
* Restore the temporary copies over the real buffers.
555564
*/
556565
if (stack->parent == NULL)
557566
{
567+
/* Splitting the root, three pages to update */
558568
MarkBufferDirty(lbuffer);
559-
memcpy(BufferGetPage(stack->buffer), newrootpg, BLCKSZ);
569+
memcpy(page, newrootpg, BLCKSZ);
560570
memcpy(BufferGetPage(lbuffer), newlpage, BLCKSZ);
561571
memcpy(BufferGetPage(rbuffer), newrpage, BLCKSZ);
562572
}
563573
else
564574
{
565-
memcpy(BufferGetPage(stack->buffer), newlpage, BLCKSZ);
575+
/* Normal split, only two pages to update */
576+
memcpy(page, newlpage, BLCKSZ);
566577
memcpy(BufferGetPage(rbuffer), newrpage, BLCKSZ);
567578
}
568579

580+
/* We also clear childbuf's INCOMPLETE_SPLIT flag, if passed */
581+
if (BufferIsValid(childbuf))
582+
{
583+
GinPageGetOpaque(childpage)->flags &= ~GIN_INCOMPLETE_SPLIT;
584+
MarkBufferDirty(childbuf);
585+
}
586+
569587
/* write WAL record */
570588
if (RelationNeedsWAL(btree->index))
571589
{
590+
XLogRecData rdata[2];
572591
XLogRecPtr recptr;
573592

593+
rdata[0].buffer = InvalidBuffer;
594+
rdata[0].data = (char *) &data;
595+
rdata[0].len = sizeof(ginxlogSplit);
596+
597+
if (BufferIsValid(childbuf))
598+
{
599+
rdata[0].next = &rdata[1];
600+
601+
rdata[1].buffer = childbuf;
602+
rdata[1].buffer_std = true;
603+
rdata[1].data = NULL;
604+
rdata[1].len = 0;
605+
rdata[1].next = payloadrdata;
606+
}
607+
else
608+
rdata[0].next = payloadrdata;
609+
574610
recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_SPLIT, rdata);
575-
PageSetLSN(BufferGetPage(stack->buffer), recptr);
611+
612+
PageSetLSN(page, recptr);
576613
PageSetLSN(BufferGetPage(rbuffer), recptr);
577614
if (stack->parent == NULL)
578615
PageSetLSN(BufferGetPage(lbuffer), recptr);
@@ -582,33 +619,31 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
582619
END_CRIT_SECTION();
583620

584621
/*
585-
* We can release the lock on the right page now, but keep the
586-
* original buffer locked.
622+
* We can release the locks/pins on the new pages now, but keep
623+
* stack->buffer locked. childbuf doesn't get unlocked either.
587624
*/
588625
UnlockReleaseBuffer(rbuffer);
589626
if (stack->parent == NULL)
590627
UnlockReleaseBuffer(lbuffer);
591628

592-
pfree(newlpage);
593-
pfree(newrpage);
594-
if (newrootpg)
595-
pfree(newrootpg);
596-
597629
/*
598630
* If we split the root, we're done. Otherwise the split is not
599631
* complete until the downlink for the new page has been inserted to
600632
* the parent.
601633
*/
602-
if (stack->parent == NULL)
603-
return true;
604-
else
605-
return false;
634+
result = (stack->parent == NULL);
606635
}
607636
else
608637
{
609-
elog(ERROR, "unknown return code from GIN placeToPage method: %d", rc);
610-
return false; /* keep compiler quiet */
638+
elog(ERROR, "invalid return code from GIN placeToPage method: %d", rc);
639+
result = false; /* keep compiler quiet */
611640
}
641+
642+
/* Clean up temp context */
643+
MemoryContextSwitchTo(oldCxt);
644+
MemoryContextDelete(tmpCxt);
645+
646+
return result;
612647
}
613648

614649
/*

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