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Replace "amgetmulti" AM functions with "amgetbitmap", in which the whole

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indexscan always occurs in one call, and the results are returned in a
TIDBitmap instead of a limited-size array of TIDs.  This should improve
speed a little by reducing AM entry/exit overhead, and it is necessary
infrastructure if we are ever to support bitmap indexes.

In an only slightly related change, add support for TIDBitmaps to preserve
(somewhat lossily) the knowledge that particular TIDs reported by an index
need to have their quals rechecked when the heap is visited.  This facility
is not really used yet; we'll need to extend the forced-recheck feature to
plain indexscans before it's useful, and that hasn't been coded yet.
The intent is to use it to clean up 8.3's horrid @@@ kluge for text search
with weighted queries.  There might be other uses in future, but that one
alone is sufficient reason.

Heikki Linnakangas, with some adjustments by me.
This commit is contained in:
Tom Lane
2008-04-10 22:25:26 +00:00
parent f260edb144
commit 4e82a95476
30 changed files with 420 additions and 269 deletions
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76
src/backend/access/hash/hash.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/hash/hash.c,v 1.100 2008/03/16 23:15:08 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/hash/hash.c,v 1.101 2008/04/10 22:25:25 tgl Exp $
*
* NOTES
* This file contains only the public interface routines.
@@ -22,6 +22,7 @@
#include "access/hash.h"
#include "catalog/index.h"
#include "commands/vacuum.h"
#include "miscadmin.h"
#include "optimizer/cost.h"
#include "optimizer/plancat.h"
@@ -275,72 +276,51 @@ hashgettuple(PG_FUNCTION_ARGS)
/*
* hashgetmulti() -- get multiple tuples at once
*
* This is a somewhat generic implementation: it avoids lock reacquisition
* overhead, but there's no smarts about picking especially good stopping
* points such as index page boundaries.
* hashgetbitmap() -- get all tuples at once
*/
Datum
hashgetmulti(PG_FUNCTION_ARGS)
hashgetbitmap(PG_FUNCTION_ARGS)
{
IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
ItemPointer tids = (ItemPointer) PG_GETARG_POINTER(1);
int32 max_tids = PG_GETARG_INT32(2);
int32 *returned_tids = (int32 *) PG_GETARG_POINTER(3);
TIDBitmap *tbm = (TIDBitmap *) PG_GETARG_POINTER(1);
HashScanOpaque so = (HashScanOpaque) scan->opaque;
Relation rel = scan->indexRelation;
bool res = true;
int32 ntids = 0;
bool res;
int64 ntids = 0;
/*
* We hold pin but not lock on current buffer while outside the hash AM.
* Reacquire the read lock here.
*/
if (BufferIsValid(so->hashso_curbuf))
_hash_chgbufaccess(rel, so->hashso_curbuf, HASH_NOLOCK, HASH_READ);
res = _hash_first(scan, ForwardScanDirection);
while (ntids < max_tids)
while (res)
{
/*
* Start scan, or advance to next tuple.
*/
if (ItemPointerIsValid(&(so->hashso_curpos)))
res = _hash_next(scan, ForwardScanDirection);
else
res = _hash_first(scan, ForwardScanDirection);
bool add_tuple;
CHECK_FOR_INTERRUPTS();
/*
* Skip killed tuples if asked to.
*/
if (scan->ignore_killed_tuples)
{
while (res)
{
Page page;
OffsetNumber offnum;
Page page;
OffsetNumber offnum;
offnum = ItemPointerGetOffsetNumber(&(so->hashso_curpos));
page = BufferGetPage(so->hashso_curbuf);
if (!ItemIdIsDead(PageGetItemId(page, offnum)))
break;
res = _hash_next(scan, ForwardScanDirection);
}
offnum = ItemPointerGetOffsetNumber(&(so->hashso_curpos));
page = BufferGetPage(so->hashso_curbuf);
add_tuple = !ItemIdIsDead(PageGetItemId(page, offnum));
}
else
add_tuple = true;
/* Save tuple ID, and continue scanning */
if (add_tuple)
{
tbm_add_tuples(tbm, &scan->xs_ctup.t_self, 1, false);
ntids++;
}
if (!res)
break;
/* Save tuple ID, and continue scanning */
tids[ntids] = scan->xs_ctup.t_self;
ntids++;
res = _hash_next(scan, ForwardScanDirection);
}
/* Release read lock on current buffer, but keep it pinned */
if (BufferIsValid(so->hashso_curbuf))
_hash_chgbufaccess(rel, so->hashso_curbuf, HASH_READ, HASH_NOLOCK);
*returned_tids = ntids;
PG_RETURN_BOOL(res);
PG_RETURN_INT64(ntids);
}