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HOT updates. When we update a tuple without changing any of its indexed

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columns, and the new version can be stored on the same heap page, we no longer
generate extra index entries for the new version.  Instead, index searches
follow the HOT-chain links to ensure they find the correct tuple version.

In addition, this patch introduces the ability to "prune" dead tuples on a
per-page basis, without having to do a complete VACUUM pass to recover space.
VACUUM is still needed to clean up dead index entries, however.

Pavan Deolasee, with help from a bunch of other people.
This commit is contained in:
Tom Lane
2007-09-20 17:56:33 +00:00
parent bbf4fdc253
commit 282d2a03dd
65 changed files with 3517 additions and 514 deletions
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104
src/backend/executor/nodeBitmapHeapscan.c
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@ -21,7 +21,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/nodeBitmapHeapscan.c,v 1.19 2007/09/12 22:10:26 tgl Exp $
* $PostgreSQL: pgsql/src/backend/executor/nodeBitmapHeapscan.c,v 1.20 2007/09/20 17:56:31 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -240,12 +240,7 @@ bitgetpage(HeapScanDesc scan, TBMIterateResult *tbmres)
BlockNumber page = tbmres->blockno;
Buffer buffer;
Snapshot snapshot;
Page dp;
int ntup;
int curslot;
int minslot;
int maxslot;
int maxoff;
/*
* Acquire pin on the target heap page, trading in any pin we held before.
@ -258,6 +253,13 @@ bitgetpage(HeapScanDesc scan, TBMIterateResult *tbmres)
buffer = scan->rs_cbuf;
snapshot = scan->rs_snapshot;
ntup = 0;
/*
* Prune and repair fragmentation for the whole page, if possible.
*/
heap_page_prune_opt(scan->rs_rd, buffer, RecentGlobalXmin);
/*
* We must hold share lock on the buffer content while examining tuple
* visibility. Afterwards, however, the tuples we have found to be
@ -265,71 +267,51 @@ bitgetpage(HeapScanDesc scan, TBMIterateResult *tbmres)
*/
LockBuffer(buffer, BUFFER_LOCK_SHARE);
dp = (Page) BufferGetPage(buffer);
maxoff = PageGetMaxOffsetNumber(dp);
/*
* Determine how many entries we need to look at on this page. If the
* bitmap is lossy then we need to look at each physical item pointer;
* otherwise we just look through the offsets listed in tbmres.
* We need two separate strategies for lossy and non-lossy cases.
*/
if (tbmres->ntuples >= 0)
{
/* non-lossy case */
minslot = 0;
maxslot = tbmres->ntuples - 1;
/*
* Bitmap is non-lossy, so we just look through the offsets listed in
* tbmres; but we have to follow any HOT chain starting at each such
* offset.
*/
int curslot;
for (curslot = 0; curslot < tbmres->ntuples; curslot++)
{
OffsetNumber offnum = tbmres->offsets[curslot];
ItemPointerData tid;
ItemPointerSet(&tid, page, offnum);
if (heap_hot_search_buffer(&tid, buffer, snapshot, NULL))
scan->rs_vistuples[ntup++] = ItemPointerGetOffsetNumber(&tid);
}
}
else
{
/* lossy case */
minslot = FirstOffsetNumber;
maxslot = maxoff;
}
/*
* Bitmap is lossy, so we must examine each item pointer on the page.
* But we can ignore HOT chains, since we'll check each tuple anyway.
*/
Page dp = (Page) BufferGetPage(buffer);
OffsetNumber maxoff = PageGetMaxOffsetNumber(dp);
OffsetNumber offnum;
ntup = 0;
for (curslot = minslot; curslot <= maxslot; curslot++)
{
OffsetNumber targoffset;
ItemId lp;
HeapTupleData loctup;
bool valid;
if (tbmres->ntuples >= 0)
for (offnum = FirstOffsetNumber; offnum <= maxoff; offnum++)
{
/* non-lossy case */
targoffset = tbmres->offsets[curslot];
ItemId lp;
HeapTupleData loctup;
lp = PageGetItemId(dp, offnum);
if (!ItemIdIsNormal(lp))
continue;
loctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lp);
loctup.t_len = ItemIdGetLength(lp);
if (HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer))
scan->rs_vistuples[ntup++] = offnum;
}
else
{
/* lossy case */
targoffset = (OffsetNumber) curslot;
}
/*
* We'd better check for out-of-range offnum in case of VACUUM since
* the TID was obtained.
*/
if (targoffset < FirstOffsetNumber || targoffset > maxoff)
continue;
lp = PageGetItemId(dp, targoffset);
/*
* Must check for deleted tuple.
*/
if (!ItemIdIsNormal(lp))
continue;
/*
* check time qualification of tuple, remember it if valid
*/
loctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lp);
loctup.t_len = ItemIdGetLength(lp);
ItemPointerSet(&(loctup.t_self), page, targoffset);
valid = HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer);
if (valid)
scan->rs_vistuples[ntup++] = targoffset;
}
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);