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Commitc38b759

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Tweak ExecIndexEvalRuntimeKeys to forcibly detoast any toasted comparison
values before they get passed to the index access method. This avoidsrepeated detoastings that will otherwise ensue as the comparison valueis examined by various index support functions. We have seen a couple ofreports of cases where repeated detoastings result in an order-of-magnitudeslowdown, so it seems worth adding a bit of extra logic to prevent this.I had previously proposed trying to avoid duplicate detoastings in general,but this fix takes care of what seems the most important case in practicewith very little effort or risk.Back-patch to 8.4 so that the PostGIS folk won't have to wait a year tohave this fix in a production release. (The issue exists further back,of course, but the code's diverged enough to make backpatching further ahigher-risk action. Also it appears that the possible gains may be limitedin prior releases because of different handling of lossy operators.)
1 parent56e985d commitc38b759

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2 files changed

+56
-33
lines changed

2 files changed

+56
-33
lines changed

‎src/backend/executor/nodeIndexscan.c

Lines changed: 54 additions & 32 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.133 2009/07/18 19:15:41 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.134 2009/08/23 18:26:08 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -238,6 +238,10 @@ ExecIndexEvalRuntimeKeys(ExprContext *econtext,
238238
IndexRuntimeKeyInfo*runtimeKeys,intnumRuntimeKeys)
239239
{
240240
intj;
241+
MemoryContextoldContext;
242+
243+
/* We want to keep the key values in per-tuple memory */
244+
oldContext=MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
241245

242246
for (j=0;j<numRuntimeKeys;j++)
243247
{
@@ -256,18 +260,32 @@ ExecIndexEvalRuntimeKeys(ExprContext *econtext,
256260
* econtext->ecxt_per_tuple_memory. We assume that the outer tuple
257261
* will stay put throughout our scan. If this is wrong, we could copy
258262
* the result into our context explicitly, but I think that's not
259-
* necessary...
263+
* necessary.
264+
*
265+
* It's also entirely possible that the result of the eval is a
266+
* toasted value. In this case we should forcibly detoast it,
267+
* to avoid repeat detoastings each time the value is examined
268+
* by an index support function.
260269
*/
261-
scanvalue=ExecEvalExprSwitchContext(key_expr,
262-
econtext,
263-
&isNull,
264-
NULL);
265-
scan_key->sk_argument=scanvalue;
270+
scanvalue=ExecEvalExpr(key_expr,
271+
econtext,
272+
&isNull,
273+
NULL);
266274
if (isNull)
275+
{
276+
scan_key->sk_argument=scanvalue;
267277
scan_key->sk_flags |=SK_ISNULL;
278+
}
268279
else
280+
{
281+
if (runtimeKeys[j].key_toastable)
282+
scanvalue=PointerGetDatum(PG_DETOAST_DATUM(scanvalue));
283+
scan_key->sk_argument=scanvalue;
269284
scan_key->sk_flags &= ~SK_ISNULL;
285+
}
270286
}
287+
288+
MemoryContextSwitchTo(oldContext);
271289
}
272290

273291
/*
@@ -795,6 +813,8 @@ ExecIndexBuildScanKeys(PlanState *planstate, Relation index, Index scanrelid,
795813
runtime_keys[n_runtime_keys].scan_key=this_scan_key;
796814
runtime_keys[n_runtime_keys].key_expr=
797815
ExecInitExpr(rightop,planstate);
816+
runtime_keys[n_runtime_keys].key_toastable=
817+
TypeIsToastable(op_righttype);
798818
n_runtime_keys++;
799819
scanvalue= (Datum)0;
800820
}
@@ -843,6 +863,31 @@ ExecIndexBuildScanKeys(PlanState *planstate, Relation index, Index scanrelid,
843863

844864
varattno= ((Var*)leftop)->varattno;
845865

866+
/*
867+
* We have to look up the operator's associated btree support
868+
* function
869+
*/
870+
opno=lfirst_oid(opnos_cell);
871+
opnos_cell=lnext(opnos_cell);
872+
873+
if (index->rd_rel->relam!=BTREE_AM_OID||
874+
varattno<1||varattno>index->rd_index->indnatts)
875+
elog(ERROR,"bogus RowCompare index qualification");
876+
opfamily=index->rd_opfamily[varattno-1];
877+
878+
get_op_opfamily_properties(opno,opfamily,
879+
&op_strategy,
880+
&op_lefttype,
881+
&op_righttype);
882+
883+
if (op_strategy!=rc->rctype)
884+
elog(ERROR,"RowCompare index qualification contains wrong operator");
885+
886+
opfuncid=get_opfamily_proc(opfamily,
887+
op_lefttype,
888+
op_righttype,
889+
BTORDER_PROC);
890+
846891
/*
847892
* rightop is the constant or variable comparison value
848893
*/
@@ -867,35 +912,12 @@ ExecIndexBuildScanKeys(PlanState *planstate, Relation index, Index scanrelid,
867912
runtime_keys[n_runtime_keys].scan_key=this_sub_key;
868913
runtime_keys[n_runtime_keys].key_expr=
869914
ExecInitExpr(rightop,planstate);
915+
runtime_keys[n_runtime_keys].key_toastable=
916+
TypeIsToastable(op_righttype);
870917
n_runtime_keys++;
871918
scanvalue= (Datum)0;
872919
}
873920

874-
/*
875-
* We have to look up the operator's associated btree support
876-
* function
877-
*/
878-
opno=lfirst_oid(opnos_cell);
879-
opnos_cell=lnext(opnos_cell);
880-
881-
if (index->rd_rel->relam!=BTREE_AM_OID||
882-
varattno<1||varattno>index->rd_index->indnatts)
883-
elog(ERROR,"bogus RowCompare index qualification");
884-
opfamily=index->rd_opfamily[varattno-1];
885-
886-
get_op_opfamily_properties(opno,opfamily,
887-
&op_strategy,
888-
&op_lefttype,
889-
&op_righttype);
890-
891-
if (op_strategy!=rc->rctype)
892-
elog(ERROR,"RowCompare index qualification contains wrong operator");
893-
894-
opfuncid=get_opfamily_proc(opfamily,
895-
op_lefttype,
896-
op_righttype,
897-
BTORDER_PROC);
898-
899921
/*
900922
* initialize the subsidiary scan key's fields appropriately
901923
*/

‎src/include/nodes/execnodes.h

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.206 2009/08/06 20:44:31 tgl Exp $
10+
* $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.207 2009/08/23 18:26:08 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -1084,6 +1084,7 @@ typedef struct
10841084
{
10851085
ScanKeyscan_key;/* scankey to put value into */
10861086
ExprState*key_expr;/* expr to evaluate to get value */
1087+
boolkey_toastable;/* is expr's result a toastable datatype? */
10871088
}IndexRuntimeKeyInfo;
10881089

10891090
typedefstruct

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