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Commitcbca6c4

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Fix for bug #866. 7.3 contains new logic for avoiding redundant calls to
the index AM when we know we are fetching a unique row. However, thislogic did not consider the possibility that it would be asked to fetchbackwards. Also fix mark/restore to work correctly in this scenario.
1 parent9270f1c commitcbca6c4

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3 files changed

+58
-11
lines changed

3 files changed

+58
-11
lines changed

‎src/backend/access/index/genam.c

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/access/index/genam.c,v 1.36 2002/09/04 20:31:09 momjian Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/access/index/genam.c,v 1.37 2003/01/08 19:41:40 tgl Exp $
1212
*
1313
* NOTES
1414
* many of the old access method routines have been turned into
@@ -107,6 +107,9 @@ RelationGetIndexScan(Relation indexRelation,
107107
/* mark cached function lookup data invalid; it will be set later */
108108
scan->fn_getnext.fn_oid=InvalidOid;
109109

110+
scan->unique_tuple_pos=0;
111+
scan->unique_tuple_mark=0;
112+
110113
pgstat_initstats(&scan->xs_pgstat_info,indexRelation);
111114

112115
/*

‎src/backend/access/index/indexam.c

Lines changed: 44 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/access/index/indexam.c,v 1.62 2002/09/04 20:31:09 momjian Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/access/index/indexam.c,v 1.63 2003/01/08 19:41:40 tgl Exp $
1212
*
1313
* INTERFACE ROUTINES
1414
*index_open- open an index relation by relation OID
@@ -308,6 +308,8 @@ index_rescan(IndexScanDesc scan, ScanKey key)
308308
scan->kill_prior_tuple= false;/* for safety */
309309
scan->keys_are_unique= false;/* may be set by amrescan */
310310
scan->got_tuple= false;
311+
scan->unique_tuple_pos=0;
312+
scan->unique_tuple_mark=0;
311313

312314
OidFunctionCall2(procedure,
313315
PointerGetDatum(scan),
@@ -360,6 +362,8 @@ index_markpos(IndexScanDesc scan)
360362
SCAN_CHECKS;
361363
GET_SCAN_PROCEDURE(markpos,ammarkpos);
362364

365+
scan->unique_tuple_mark=scan->unique_tuple_pos;
366+
363367
OidFunctionCall1(procedure,PointerGetDatum(scan));
364368
}
365369

@@ -376,7 +380,13 @@ index_restrpos(IndexScanDesc scan)
376380
GET_SCAN_PROCEDURE(restrpos,amrestrpos);
377381

378382
scan->kill_prior_tuple= false;/* for safety */
379-
scan->got_tuple= false;
383+
384+
/*
385+
* We do not reset got_tuple; so if the scan is actually being
386+
* short-circuited by index_getnext, the effective position restoration
387+
* is done by restoring unique_tuple_pos.
388+
*/
389+
scan->unique_tuple_pos=scan->unique_tuple_mark;
380390

381391
OidFunctionCall1(procedure,PointerGetDatum(scan));
382392
}
@@ -398,6 +408,32 @@ index_getnext(IndexScanDesc scan, ScanDirection direction)
398408

399409
SCAN_CHECKS;
400410

411+
/*
412+
* Can skip entering the index AM if we already got a tuple and it
413+
* must be unique. Instead, we need a "short circuit" path that
414+
* just keeps track of logical scan position (before/on/after tuple).
415+
*
416+
* Note that we hold the pin on the single tuple's buffer throughout
417+
* the scan once we are in this state.
418+
*/
419+
if (scan->keys_are_unique&&scan->got_tuple)
420+
{
421+
if (ScanDirectionIsForward(direction))
422+
{
423+
if (scan->unique_tuple_pos <=0)
424+
scan->unique_tuple_pos++;
425+
}
426+
elseif (ScanDirectionIsBackward(direction))
427+
{
428+
if (scan->unique_tuple_pos >=0)
429+
scan->unique_tuple_pos--;
430+
}
431+
if (scan->unique_tuple_pos==0)
432+
returnheapTuple;
433+
else
434+
returnNULL;
435+
}
436+
401437
/* Release any previously held pin */
402438
if (BufferIsValid(scan->xs_cbuf))
403439
{
@@ -408,13 +444,6 @@ index_getnext(IndexScanDesc scan, ScanDirection direction)
408444
/* just make sure this is false... */
409445
scan->kill_prior_tuple= false;
410446

411-
/*
412-
* Can skip entering the index AM if we already got a tuple and it
413-
* must be unique.
414-
*/
415-
if (scan->keys_are_unique&&scan->got_tuple)
416-
returnNULL;
417-
418447
for (;;)
419448
{
420449
boolfound;
@@ -475,6 +504,12 @@ index_getnext(IndexScanDesc scan, ScanDirection direction)
475504
/* Success exit */
476505
scan->got_tuple= true;
477506

507+
/*
508+
* If we just fetched a known-unique tuple, then subsequent calls will
509+
* go through the short-circuit code above. unique_tuple_pos has been
510+
* initialized to 0, which is the correct state ("on row").
511+
*/
512+
478513
pgstat_count_index_getnext(&scan->xs_pgstat_info);
479514

480515
returnheapTuple;

‎src/include/access/relscan.h

Lines changed: 10 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $Id: relscan.h,v 1.29 2002/09/04 20:31:37 momjian Exp $
10+
* $Id: relscan.h,v 1.30 2003/01/08 19:41:40 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -70,6 +70,15 @@ typedef struct IndexScanDescData
7070

7171
FmgrInfofn_getnext;/* cached lookup info for AM's getnext fn */
7272

73+
/*
74+
* If keys_are_unique and got_tuple are both true, we stop calling the
75+
* index AM; it is then necessary for index_getnext to keep track of
76+
* the logical scan position for itself. It does that using
77+
* unique_tuple_pos: -1 = before row, 0 = on row, +1 = after row.
78+
*/
79+
intunique_tuple_pos;/* logical position */
80+
intunique_tuple_mark;/* logical marked position */
81+
7382
PgStat_Infoxs_pgstat_info;/* statistics collector hook */
7483
}IndexScanDescData;
7584

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