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Commit7772dec

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Fix nbtree metapage cache upgrade bug.
Commit857f9c3, which taught nbtree VACUUM to avoid unnecessaryindex scans, bumped the nbtree version number from 2 to 3, while addingthe ability for nbtree indexes to be upgraded on-the-fly. Variousassertions that assumed that an nbtree index was always on version 2 hadto be changed to accept any supported version (version 2 or 3 onPostgres 11).However, a few assertions were missed in the initial commit, all ofwhich were in code paths that cache a local copy of the metapagemetadata, where the index had been expected to be on the current version(no longer version 2) as a generic sanity check. Rather than simplyupdate the assertions, follow-up commit0a64b45 intentionally madethe metapage caching code update the per-backend cached metadata versionwithout changing the on-disk version at the same time. This could evenhappen when the planner needed to determine the height of a B-Tree forcosting purposes. The assertions only fail on Postgres v12 whenupgrading from v10, because they were adjusted to use the authoritativeshared memory metapage by v12's commitdd299df.To fix, remove the cache-only upgrade mechanism entirely, and update theassertions themselves to accept any supported version (go back to usingthe cached version in v12). The fix is almost a full revert of commit0a64b45 on the v11 branch.VACUUM only considers the authoritative metapage, and never bothers witha locally cached version, whereas everywhere else isn't interested inthe metapage fields that were added by commit857f9c3. It seemsunlikely that this bug has affected any user on v11.Reported-By: Christoph BergBug: #15896Discussion:https://postgr.es/m/15896-5b25e260fdb0b081%40postgresql.orgBackpatch: 11-, where VACUUM was taught to avoid unnecessary index scans.
1 parent79d3a1e commit7772dec

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3 files changed

+40
-77
lines changed

3 files changed

+40
-77
lines changed

‎src/backend/access/nbtree/nbtpage.c‎

Lines changed: 36 additions & 75 deletions
Original file line numberDiff line numberDiff line change
@@ -33,7 +33,6 @@
3333
#include"storage/predicate.h"
3434
#include"utils/snapmgr.h"
3535

36-
staticvoid_bt_cachemetadata(Relationrel,BTMetaPageData*input);
3736
staticBTMetaPageData*_bt_getmeta(Relationrel,Buffermetabuf);
3837
staticbool_bt_mark_page_halfdead(Relationrel,Bufferbuf,BTStackstack);
3938
staticbool_bt_unlink_halfdead_page(Relationrel,Bufferleafbuf,
@@ -109,48 +108,13 @@ _bt_upgrademetapage(Page page)
109108
((char*)metad+sizeof(BTMetaPageData))- (char*)page;
110109
}
111110

112-
/*
113-
* Cache metadata from input meta page to rel->rd_amcache.
114-
*/
115-
staticvoid
116-
_bt_cachemetadata(Relationrel,BTMetaPageData*input)
117-
{
118-
BTMetaPageData*cached_metad;
119-
120-
/* We assume rel->rd_amcache was already freed by caller */
121-
Assert(rel->rd_amcache==NULL);
122-
rel->rd_amcache=MemoryContextAlloc(rel->rd_indexcxt,
123-
sizeof(BTMetaPageData));
124-
125-
/* Meta page should be of supported version */
126-
Assert(input->btm_version >=BTREE_MIN_VERSION&&
127-
input->btm_version <=BTREE_VERSION);
128-
129-
cached_metad= (BTMetaPageData*)rel->rd_amcache;
130-
if (input->btm_version >=BTREE_NOVAC_VERSION)
131-
{
132-
/* Version with compatible meta-data, no need to upgrade */
133-
memcpy(cached_metad,input,sizeof(BTMetaPageData));
134-
}
135-
else
136-
{
137-
/*
138-
* Upgrade meta-data: copy available information from meta-page and
139-
* fill new fields with default values.
140-
*
141-
* Note that we cannot upgrade to version 4+ without a REINDEX, since
142-
* extensive on-disk changes are required.
143-
*/
144-
memcpy(cached_metad,input, offsetof(BTMetaPageData,btm_oldest_btpo_xact));
145-
cached_metad->btm_version=BTREE_NOVAC_VERSION;
146-
cached_metad->btm_oldest_btpo_xact=InvalidTransactionId;
147-
cached_metad->btm_last_cleanup_num_heap_tuples=-1.0;
148-
}
149-
}
150-
151111
/*
152112
* Get metadata from share-locked buffer containing metapage, while performing
153-
* standard sanity checks. Sanity checks here must match _bt_getroot().
113+
* standard sanity checks.
114+
*
115+
* Callers that cache data returned here in local cache should note that an
116+
* on-the-fly upgrade using _bt_upgrademetapage() can change the version field
117+
* and BTREE_NOVAC_VERSION specific fields without invalidating local cache.
154118
*/
155119
staticBTMetaPageData*
156120
_bt_getmeta(Relationrel,Buffermetabuf)
@@ -293,8 +257,6 @@ Buffer
293257
_bt_getroot(Relationrel,intaccess)
294258
{
295259
Buffermetabuf;
296-
Pagemetapg;
297-
BTPageOpaquemetaopaque;
298260
Bufferrootbuf;
299261
Pagerootpage;
300262
BTPageOpaquerootopaque;
@@ -347,30 +309,13 @@ _bt_getroot(Relation rel, int access)
347309
}
348310

349311
metabuf=_bt_getbuf(rel,BTREE_METAPAGE,BT_READ);
350-
metapg=BufferGetPage(metabuf);
351-
metaopaque= (BTPageOpaque)PageGetSpecialPointer(metapg);
352-
metad=BTPageGetMeta(metapg);
353-
354-
/* sanity-check the metapage */
355-
if (!P_ISMETA(metaopaque)||
356-
metad->btm_magic!=BTREE_MAGIC)
357-
ereport(ERROR,
358-
(errcode(ERRCODE_INDEX_CORRUPTED),
359-
errmsg("index \"%s\" is not a btree",
360-
RelationGetRelationName(rel))));
361-
362-
if (metad->btm_version<BTREE_MIN_VERSION||
363-
metad->btm_version>BTREE_VERSION)
364-
ereport(ERROR,
365-
(errcode(ERRCODE_INDEX_CORRUPTED),
366-
errmsg("version mismatch in index \"%s\": file version %d, "
367-
"current version %d, minimal supported version %d",
368-
RelationGetRelationName(rel),
369-
metad->btm_version,BTREE_VERSION,BTREE_MIN_VERSION)));
312+
metad=_bt_getmeta(rel,metabuf);
370313

371314
/* if no root page initialized yet, do it */
372315
if (metad->btm_root==P_NONE)
373316
{
317+
Pagemetapg;
318+
374319
/* If access = BT_READ, caller doesn't want us to create root yet */
375320
if (access==BT_READ)
376321
{
@@ -412,6 +357,8 @@ _bt_getroot(Relation rel, int access)
412357
rootopaque->btpo_flags= (BTP_LEAF |BTP_ROOT);
413358
rootopaque->btpo.level=0;
414359
rootopaque->btpo_cycleid=0;
360+
/* Get raw page pointer for metapage */
361+
metapg=BufferGetPage(metabuf);
415362

416363
/* NO ELOG(ERROR) till meta is updated */
417364
START_CRIT_SECTION();
@@ -473,7 +420,7 @@ _bt_getroot(Relation rel, int access)
473420
LockBuffer(rootbuf,BUFFER_LOCK_UNLOCK);
474421
LockBuffer(rootbuf,BT_READ);
475422

476-
/* okay, metadata is correct, release lock on it */
423+
/* okay, metadata is correct, release lock on itwithout caching*/
477424
_bt_relbuf(rel,metabuf);
478425
}
479426
else
@@ -485,7 +432,9 @@ _bt_getroot(Relation rel, int access)
485432
/*
486433
* Cache the metapage data for next time
487434
*/
488-
_bt_cachemetadata(rel,metad);
435+
rel->rd_amcache=MemoryContextAlloc(rel->rd_indexcxt,
436+
sizeof(BTMetaPageData));
437+
memcpy(rel->rd_amcache,metad,sizeof(BTMetaPageData));
489438

490439
/*
491440
* We are done with the metapage; arrange to release it via first
@@ -659,16 +608,19 @@ _bt_getrootheight(Relation rel)
659608
/*
660609
* Cache the metapage data for next time
661610
*/
662-
_bt_cachemetadata(rel,metad);
663-
/* We shouldn't have cached it if any of these fail */
664-
Assert(metad->btm_magic==BTREE_MAGIC);
665-
Assert(metad->btm_version >=BTREE_NOVAC_VERSION);
666-
Assert(metad->btm_fastroot!=P_NONE);
611+
rel->rd_amcache=MemoryContextAlloc(rel->rd_indexcxt,
612+
sizeof(BTMetaPageData));
613+
memcpy(rel->rd_amcache,metad,sizeof(BTMetaPageData));
667614
_bt_relbuf(rel,metabuf);
668615
}
669616

670617
/* Get cached page */
671618
metad= (BTMetaPageData*)rel->rd_amcache;
619+
/* We shouldn't have cached it if any of these fail */
620+
Assert(metad->btm_magic==BTREE_MAGIC);
621+
Assert(metad->btm_version >=BTREE_MIN_VERSION);
622+
Assert(metad->btm_version <=BTREE_VERSION);
623+
Assert(metad->btm_fastroot!=P_NONE);
672624

673625
returnmetad->btm_fastlevel;
674626
}
@@ -709,17 +661,26 @@ _bt_heapkeyspace(Relation rel)
709661

710662
/*
711663
* Cache the metapage data for next time
664+
*
665+
* An on-the-fly version upgrade performed by _bt_upgrademetapage()
666+
* can change the nbtree version for an index without invalidating any
667+
* local cache. This is okay because it can only happen when moving
668+
* from version 2 to version 3, both of which are !heapkeyspace
669+
* versions.
712670
*/
713-
_bt_cachemetadata(rel,metad);
714-
/* We shouldn't have cached it if any of these fail */
715-
Assert(metad->btm_magic==BTREE_MAGIC);
716-
Assert(metad->btm_version >=BTREE_NOVAC_VERSION);
717-
Assert(metad->btm_fastroot!=P_NONE);
671+
rel->rd_amcache=MemoryContextAlloc(rel->rd_indexcxt,
672+
sizeof(BTMetaPageData));
673+
memcpy(rel->rd_amcache,metad,sizeof(BTMetaPageData));
718674
_bt_relbuf(rel,metabuf);
719675
}
720676

721677
/* Get cached page */
722678
metad= (BTMetaPageData*)rel->rd_amcache;
679+
/* We shouldn't have cached it if any of these fail */
680+
Assert(metad->btm_magic==BTREE_MAGIC);
681+
Assert(metad->btm_version >=BTREE_MIN_VERSION);
682+
Assert(metad->btm_version <=BTREE_VERSION);
683+
Assert(metad->btm_fastroot!=P_NONE);
723684

724685
returnmetad->btm_version>BTREE_NOVAC_VERSION;
725686
}

‎src/backend/access/nbtree/nbtxlog.c‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -107,6 +107,8 @@ _bt_restore_meta(XLogReaderState *record, uint8 block_id)
107107
md->btm_level=xlrec->level;
108108
md->btm_fastroot=xlrec->fastroot;
109109
md->btm_fastlevel=xlrec->fastlevel;
110+
/* Cannot log BTREE_MIN_VERSION index metapage without upgrade */
111+
Assert(md->btm_version >=BTREE_NOVAC_VERSION);
110112
md->btm_oldest_btpo_xact=xlrec->oldest_btpo_xact;
111113
md->btm_last_cleanup_num_heap_tuples=xlrec->last_cleanup_num_heap_tuples;
112114

‎src/include/access/nbtree.h‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -97,12 +97,12 @@ typedef BTPageOpaqueData *BTPageOpaque;
9797
typedefstructBTMetaPageData
9898
{
9999
uint32btm_magic;/* should contain BTREE_MAGIC */
100-
uint32btm_version;/*should containBTREE_VERSION */
100+
uint32btm_version;/*nbtree version (always <=BTREE_VERSION) */
101101
BlockNumberbtm_root;/* current root location */
102102
uint32btm_level;/* tree level of the root page */
103103
BlockNumberbtm_fastroot;/* current "fast" root location */
104104
uint32btm_fastlevel;/* tree level of the "fast" root page */
105-
/*following fieldsare available since page version 3 */
105+
/*remaining fieldsonly valid when btm_version >= BTREE_NOVAC_VERSION */
106106
TransactionIdbtm_oldest_btpo_xact;/* oldest btpo_xact among all deleted
107107
* pages */
108108
float8btm_last_cleanup_num_heap_tuples;/* number of heap tuples

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