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Commitc17abc1

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Fix logic error in tbm_intersect: the intersection of a normal page and
a lossy page has to be lossy, because we don't know exactly which tupleson the page should remain part of the bitmap. Per Jie Zhang.
1 parenteaa5d52 commitc17abc1

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1 file changed

+23
-6
lines changed

1 file changed

+23
-6
lines changed

‎src/backend/nodes/tidbitmap.c

Lines changed: 23 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -23,7 +23,7 @@
2323
* Copyright (c) 2003-2005, PostgreSQL Global Development Group
2424
*
2525
* IDENTIFICATION
26-
* $PostgreSQL: pgsql/src/backend/nodes/tidbitmap.c,v 1.4 2005/05/29 04:23:03 tgl Exp $
26+
* $PostgreSQL: pgsql/src/backend/nodes/tidbitmap.c,v 1.5 2005/07/24 02:25:26 tgl Exp $
2727
*
2828
*-------------------------------------------------------------------------
2929
*/
@@ -135,7 +135,8 @@ struct TIDBitmap
135135

136136
/* Local function prototypes */
137137
staticvoidtbm_union_page(TIDBitmap*a,constPagetableEntry*bpage);
138-
staticbooltbm_intersect_page(PagetableEntry*apage,constTIDBitmap*b);
138+
staticbooltbm_intersect_page(TIDBitmap*a,PagetableEntry*apage,
139+
constTIDBitmap*b);
139140
staticconstPagetableEntry*tbm_find_pageentry(constTIDBitmap*tbm,
140141
BlockNumberpageno);
141142
staticPagetableEntry*tbm_get_pageentry(TIDBitmap*tbm,BlockNumberpageno);
@@ -382,7 +383,7 @@ tbm_intersect(TIDBitmap *a, const TIDBitmap *b)
382383
/* Scan through chunks and pages in a, try to match to b */
383384
if (a->status==TBM_ONE_PAGE)
384385
{
385-
if (tbm_intersect_page(&a->entry1,b))
386+
if (tbm_intersect_page(a,&a->entry1,b))
386387
{
387388
/* Page is now empty, remove it from a */
388389
Assert(!a->entry1.ischunk);
@@ -401,7 +402,7 @@ tbm_intersect(TIDBitmap *a, const TIDBitmap *b)
401402
hash_seq_init(&status,a->pagetable);
402403
while ((apage= (PagetableEntry*)hash_seq_search(&status))!=NULL)
403404
{
404-
if (tbm_intersect_page(apage,b))
405+
if (tbm_intersect_page(a,apage,b))
405406
{
406407
/* Page or chunk is now empty, remove it from a */
407408
if (apage->ischunk)
@@ -424,7 +425,7 @@ tbm_intersect(TIDBitmap *a, const TIDBitmap *b)
424425
* Returns TRUE if apage is now empty and should be deleted from a
425426
*/
426427
staticbool
427-
tbm_intersect_page(PagetableEntry*apage,constTIDBitmap*b)
428+
tbm_intersect_page(TIDBitmap*a,PagetableEntry*apage,constTIDBitmap*b)
428429
{
429430
constPagetableEntry*bpage;
430431
intwordnum;
@@ -470,7 +471,23 @@ tbm_intersect_page(PagetableEntry *apage, const TIDBitmap *b)
470471
}
471472
elseif (tbm_page_is_lossy(b,apage->blockno))
472473
{
473-
/* page is lossy in b, cannot clear any bits */
474+
/*
475+
* When the page is lossy in b, we have to mark it lossy in a too.
476+
* We know that no bits need be set in bitmap a, but we do not know
477+
* which ones should be cleared, and we have no API for "at most
478+
* these tuples need be checked". (Perhaps it's worth adding that?)
479+
*/
480+
tbm_mark_page_lossy(a,apage->blockno);
481+
482+
/*
483+
* Note: tbm_mark_page_lossy will have removed apage from a, and
484+
* may have inserted a new lossy chunk instead. We can continue the
485+
* same seq_search scan at the caller level, because it does not
486+
* matter whether we visit such a new chunk or not: it will have
487+
* only the bit for apage->blockno set, which is correct.
488+
*
489+
* We must return false here since apage was already deleted.
490+
*/
474491
return false;
475492
}
476493
else

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