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Avoid retrieving dummy NULL columns in postgres_fdw.
This should provide some marginal overall savings, since it surely takes many more cycles for the remote server to deal with the NULL columns than it takes for postgres_fdw not to emit them. But really the reason is to keep the emitted queries from looking quite so silly ...
1 parent 9cbc4b8 commit e690b95

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5 files changed

+301
-218
lines changed

5 files changed

+301
-218
lines changed

‎contrib/postgres_fdw/deparse.c

Lines changed: 69 additions & 26 deletions
Original file line numberDiff line numberDiff line change
@@ -106,10 +106,12 @@ static void deparseTargetList(StringInfo buf,
106106
PlannerInfo *root,
107107
Index rtindex,
108108
Relation rel,
109-
Bitmapset *attrs_used);
109+
Bitmapset *attrs_used,
110+
List **retrieved_attrs);
110111
static void deparseReturningList(StringInfo buf, PlannerInfo *root,
111112
Index rtindex, Relation rel,
112-
List *returningList);
113+
List *returningList,
114+
List **retrieved_attrs);
113115
static void deparseColumnRef(StringInfo buf, int varno, int varattno,
114116
PlannerInfo *root);
115117
static void deparseRelation(StringInfo buf, Relation rel);
@@ -652,12 +654,16 @@ is_builtin(Oid oid)
652654
* Construct a simple SELECT statement that retrieves desired columns
653655
* of the specified foreign table, and append it to "buf". The output
654656
* contains just "SELECT ... FROM tablename".
657+
*
658+
* We also create an integer List of the columns being retrieved, which is
659+
* returned to *retrieved_attrs.
655660
*/
656661
void
657662
deparseSelectSql(StringInfo buf,
658663
PlannerInfo *root,
659664
RelOptInfo *baserel,
660-
Bitmapset *attrs_used)
665+
Bitmapset *attrs_used,
666+
List **retrieved_attrs)
661667
{
662668
RangeTblEntry *rte = planner_rt_fetch(baserel->relid, root);
663669
Relation rel;
@@ -672,7 +678,8 @@ deparseSelectSql(StringInfo buf,
672678
* Construct SELECT list
673679
*/
674680
appendStringInfoString(buf, "SELECT ");
675-
deparseTargetList(buf, root, baserel->relid, rel, attrs_used);
681+
deparseTargetList(buf, root, baserel->relid, rel, attrs_used,
682+
retrieved_attrs);
676683

677684
/*
678685
* Construct FROM clause
@@ -687,24 +694,24 @@ deparseSelectSql(StringInfo buf,
687694
* Emit a target list that retrieves the columns specified in attrs_used.
688695
* This is used for both SELECT and RETURNING targetlists.
689696
*
690-
* We list attributes in order of the foreign table's columns, but replace
691-
* any attributes that need not be fetched with NULL constants. (We can't
692-
* just omit such attributes, or we'll lose track of which columns are
693-
* which at runtime.) Note however that any dropped columns are ignored.
694-
* Also, if ctid needs to be retrieved, it's added at the end.
697+
* The tlist text is appended to buf, and we also create an integer List
698+
* of the columns being retrieved, which is returned to *retrieved_attrs.
695699
*/
696700
static void
697701
deparseTargetList(StringInfo buf,
698702
PlannerInfo *root,
699703
Index rtindex,
700704
Relation rel,
701-
Bitmapset *attrs_used)
705+
Bitmapset *attrs_used,
706+
List **retrieved_attrs)
702707
{
703708
TupleDesc tupdesc = RelationGetDescr(rel);
704709
bool have_wholerow;
705710
bool first;
706711
int i;
707712

713+
*retrieved_attrs = NIL;
714+
708715
/* If there's a whole-row reference, we'll need all the columns. */
709716
have_wholerow = bms_is_member(0 - FirstLowInvalidHeapAttributeNumber,
710717
attrs_used);
@@ -718,16 +725,18 @@ deparseTargetList(StringInfo buf,
718725
if (attr->attisdropped)
719726
continue;
720727

721-
if (!first)
722-
appendStringInfoString(buf, ", ");
723-
first = false;
724-
725728
if (have_wholerow ||
726729
bms_is_member(i - FirstLowInvalidHeapAttributeNumber,
727730
attrs_used))
731+
{
732+
if (!first)
733+
appendStringInfoString(buf, ", ");
734+
first = false;
735+
728736
deparseColumnRef(buf, rtindex, i, root);
729-
else
730-
appendStringInfoString(buf, "NULL");
737+
738+
*retrieved_attrs = lappend_int(*retrieved_attrs, i);
739+
}
731740
}
732741

733742
/*
@@ -742,6 +751,9 @@ deparseTargetList(StringInfo buf,
742751
first = false;
743752

744753
appendStringInfoString(buf, "ctid");
754+
755+
*retrieved_attrs = lappend_int(*retrieved_attrs,
756+
SelfItemPointerAttributeNumber);
745757
}
746758

747759
/* Don't generate bad syntax if no undropped columns */
@@ -809,11 +821,16 @@ appendWhereClause(StringInfo buf,
809821

810822
/*
811823
* deparse remote INSERT statement
824+
*
825+
* The statement text is appended to buf, and we also create an integer List
826+
* of the columns being retrieved by RETURNING (if any), which is returned
827+
* to *retrieved_attrs.
812828
*/
813829
void
814830
deparseInsertSql(StringInfo buf, PlannerInfo *root,
815831
Index rtindex, Relation rel,
816-
List *targetAttrs, List *returningList)
832+
List *targetAttrs, List *returningList,
833+
List **retrieved_attrs)
817834
{
818835
AttrNumber pindex;
819836
bool first;
@@ -858,16 +875,24 @@ deparseInsertSql(StringInfo buf, PlannerInfo *root,
858875
appendStringInfoString(buf, " DEFAULT VALUES");
859876

860877
if (returningList)
861-
deparseReturningList(buf, root, rtindex, rel, returningList);
878+
deparseReturningList(buf, root, rtindex, rel, returningList,
879+
retrieved_attrs);
880+
else
881+
*retrieved_attrs = NIL;
862882
}
863883

864884
/*
865885
* deparse remote UPDATE statement
886+
*
887+
* The statement text is appended to buf, and we also create an integer List
888+
* of the columns being retrieved by RETURNING (if any), which is returned
889+
* to *retrieved_attrs.
866890
*/
867891
void
868892
deparseUpdateSql(StringInfo buf, PlannerInfo *root,
869893
Index rtindex, Relation rel,
870-
List *targetAttrs, List *returningList)
894+
List *targetAttrs, List *returningList,
895+
List **retrieved_attrs)
871896
{
872897
AttrNumber pindex;
873898
bool first;
@@ -894,23 +919,34 @@ deparseUpdateSql(StringInfo buf, PlannerInfo *root,
894919
appendStringInfoString(buf, " WHERE ctid = $1");
895920

896921
if (returningList)
897-
deparseReturningList(buf, root, rtindex, rel, returningList);
922+
deparseReturningList(buf, root, rtindex, rel, returningList,
923+
retrieved_attrs);
924+
else
925+
*retrieved_attrs = NIL;
898926
}
899927

900928
/*
901929
* deparse remote DELETE statement
930+
*
931+
* The statement text is appended to buf, and we also create an integer List
932+
* of the columns being retrieved by RETURNING (if any), which is returned
933+
* to *retrieved_attrs.
902934
*/
903935
void
904936
deparseDeleteSql(StringInfo buf, PlannerInfo *root,
905937
Index rtindex, Relation rel,
906-
List *returningList)
938+
List *returningList,
939+
List **retrieved_attrs)
907940
{
908941
appendStringInfoString(buf, "DELETE FROM ");
909942
deparseRelation(buf, rel);
910943
appendStringInfoString(buf, " WHERE ctid = $1");
911944

912945
if (returningList)
913-
deparseReturningList(buf, root, rtindex, rel, returningList);
946+
deparseReturningList(buf, root, rtindex, rel, returningList,
947+
retrieved_attrs);
948+
else
949+
*retrieved_attrs = NIL;
914950
}
915951

916952
/*
@@ -919,7 +955,8 @@ deparseDeleteSql(StringInfo buf, PlannerInfo *root,
919955
static void
920956
deparseReturningList(StringInfo buf, PlannerInfo *root,
921957
Index rtindex, Relation rel,
922-
List *returningList)
958+
List *returningList,
959+
List **retrieved_attrs)
923960
{
924961
Bitmapset *attrs_used;
925962

@@ -931,7 +968,8 @@ deparseReturningList(StringInfo buf, PlannerInfo *root,
931968
&attrs_used);
932969

933970
appendStringInfoString(buf, " RETURNING ");
934-
deparseTargetList(buf, root, rtindex, rel, attrs_used);
971+
deparseTargetList(buf, root, rtindex, rel, attrs_used,
972+
retrieved_attrs);
935973
}
936974

937975
/*
@@ -959,10 +997,11 @@ deparseAnalyzeSizeSql(StringInfo buf, Relation rel)
959997
/*
960998
* Construct SELECT statement to acquire sample rows of given relation.
961999
*
962-
* Note: command is appended to whatever might be in buf already.
1000+
* SELECT command is appended to buf, and list of columns retrieved
1001+
* is returned to *retrieved_attrs.
9631002
*/
9641003
void
965-
deparseAnalyzeSql(StringInfo buf, Relation rel)
1004+
deparseAnalyzeSql(StringInfo buf, Relation rel, List **retrieved_attrs)
9661005
{
9671006
Oid relid = RelationGetRelid(rel);
9681007
TupleDesc tupdesc = RelationGetDescr(rel);
@@ -972,6 +1011,8 @@ deparseAnalyzeSql(StringInfo buf, Relation rel)
9721011
ListCell *lc;
9731012
bool first = true;
9741013

1014+
*retrieved_attrs = NIL;
1015+
9751016
appendStringInfoString(buf, "SELECT ");
9761017
for (i = 0; i < tupdesc->natts; i++)
9771018
{
@@ -999,6 +1040,8 @@ deparseAnalyzeSql(StringInfo buf, Relation rel)
9991040
}
10001041

10011042
appendStringInfoString(buf, quote_identifier(colname));
1043+
1044+
*retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
10021045
}
10031046

10041047
/* Don't generate bad syntax for zero-column relation. */

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