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Replace simple constant pg_am.amcanreturn with an AM support function.
The need for this was debated when we put in the index-only-scan feature, but at the time we had no near-term expectation of having AMs that could support such scans for only some indexes; so we kept it simple. However, the SP-GiST AM forces the issue, so let's fix it. This patch only installs the new API; no behavior actually changes.
1 parent 19d2231 commit 3695a55

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15 files changed

+103
-46
lines changed

15 files changed

+103
-46
lines changed

‎doc/src/sgml/catalogs.sgml

Lines changed: 8 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -481,13 +481,6 @@
481481
<entry>Does the access method support multicolumn indexes?</entry>
482482
</row>
483483

484-
<row>
485-
<entry><structfield>amcanreturn</structfield></entry>
486-
<entry><type>bool</type></entry>
487-
<entry></entry>
488-
<entry>Can the access method return the contents of index entries?</entry>
489-
</row>
490-
491484
<row>
492485
<entry><structfield>amoptionalkey</structfield></entry>
493486
<entry><type>bool</type></entry>
@@ -622,6 +615,14 @@
622615
<entry>Post-<command>VACUUM</command> cleanup function</entry>
623616
</row>
624617

618+
<row>
619+
<entry><structfield>amcanreturn</structfield></entry>
620+
<entry><type>regproc</type></entry>
621+
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
622+
<entry>Function to check whether index supports index-only scans,
623+
or zero if none</entry>
624+
</row>
625+
625626
<row>
626627
<entry><structfield>amcostestimate</structfield></entry>
627628
<entry><type>regproc</type></entry>

‎doc/src/sgml/indexam.sgml

Lines changed: 16 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -134,11 +134,6 @@
134134
<structfield>amsearchnulls</structfield>, indicating that it supports
135135
<literal>IS NULL</> and <literal>IS NOT NULL</> clauses as search
136136
conditions.
137-
An index method can also set <structfield>amcanreturn</structfield>,
138-
indicating that it can support <firstterm>index-only scans</> by returning
139-
the indexed column values for an index entry in the form of an IndexTuple.
140-
(An example of an index AM that cannot do this is hash, which stores only
141-
the hash values not the original data.)
142137
</para>
143138

144139
</sect1>
@@ -278,6 +273,19 @@ amvacuumcleanup (IndexVacuumInfo *info,
278273

279274
<para>
280275
<programlisting>
276+
bool
277+
amcanreturn (Relation indexRelation);
278+
</programlisting>
279+
Check whether the index can support <firstterm>index-only scans</> by
280+
returning the indexed column values for an index entry in the form of an
281+
IndexTuple. Return TRUE if so, else FALSE. If the index AM can never
282+
support index-only scans (an example is hash, which stores only
283+
the hash values not the original data), it is sufficient to set its
284+
<structfield>amcanreturn</> field to zero in <structname>pg_am</>.
285+
</para>
286+
287+
<para>
288+
<programlisting>
281289
void
282290
amcostestimate (PlannerInfo *root,
283291
IndexOptInfo *index,
@@ -391,9 +399,9 @@ amgettuple (IndexScanDesc scan,
391399
</para>
392400

393401
<para>
394-
If the access method supports index-only scans (i.e.,
395-
<structfield>amcanreturn</structfield> is TRUE in its <structname>pg_am</>
396-
row), then on success it must also check
402+
If the index supports index-only scans (i.e.,
403+
<function>amcanreturn</function> returns TRUE for it),
404+
then on success the AM must also check
397405
<literal>scan-&gt;xs_want_itup</>, and if that is true it must return
398406
the original indexed data for the index entry, in the form of an
399407
<structname>IndexTuple</> pointer stored at <literal>scan-&gt;xs_itup</>,

‎src/backend/access/index/indexam.c

Lines changed: 22 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -26,6 +26,7 @@
2626
* index_getbitmap - get all tuples from a scan
2727
* index_bulk_delete - bulk deletion of index tuples
2828
* index_vacuum_cleanup - post-deletion cleanup of an index
29+
* index_can_return - does index support index-only scans?
2930
* index_getprocid - get a support procedure OID
3031
* index_getprocinfo - get a support procedure's lookup info
3132
*
@@ -711,6 +712,27 @@ index_vacuum_cleanup(IndexVacuumInfo *info,
711712
return result;
712713
}
713714

715+
/* ----------------
716+
* index_can_return - does index support index-only scans?
717+
* ----------------
718+
*/
719+
bool
720+
index_can_return(Relation indexRelation)
721+
{
722+
FmgrInfo *procedure;
723+
724+
RELATION_CHECKS;
725+
726+
/* amcanreturn is optional; assume FALSE if not provided by AM */
727+
if (!RegProcedureIsValid(indexRelation->rd_am->amcanreturn))
728+
return false;
729+
730+
GET_REL_PROCEDURE(amcanreturn);
731+
732+
return DatumGetBool(FunctionCall1(procedure,
733+
PointerGetDatum(indexRelation)));
734+
}
735+
714736
/* ----------------
715737
* index_getprocid
716738
*

‎src/backend/access/nbtree/nbtree.c

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1091,3 +1091,14 @@ btvacuumpage(BTVacState *vstate, BlockNumber blkno, BlockNumber orig_blkno)
10911091
goto restart;
10921092
}
10931093
}
1094+
1095+
/*
1096+
* btcanreturn() -- Check whether btree indexes support index-only scans.
1097+
*
1098+
* btrees always do, so this is trivial.
1099+
*/
1100+
Datum
1101+
btcanreturn(PG_FUNCTION_ARGS)
1102+
{
1103+
PG_RETURN_BOOL(true);
1104+
}

‎src/backend/access/spgist/spgscan.c

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -559,3 +559,10 @@ spggettuple(PG_FUNCTION_ARGS)
559559

560560
PG_RETURN_BOOL(false);
561561
}
562+
563+
Datum
564+
spgcanreturn(PG_FUNCTION_ARGS)
565+
{
566+
/* Not implemented yet */
567+
PG_RETURN_BOOL(false);
568+
}

‎src/backend/optimizer/path/indxpath.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1075,10 +1075,10 @@ check_index_only(RelOptInfo *rel, IndexOptInfo *index)
10751075
ListCell *lc;
10761076
int i;
10771077

1078-
/* Index-only scans must be enabled, and AM must be capable of it */
1078+
/* Index-only scans must be enabled, and index must be capable of them */
10791079
if (!enable_indexonlyscan)
10801080
return false;
1081-
if (!index->amcanreturn)
1081+
if (!index->canreturn)
10821082
return false;
10831083

10841084
/*

‎src/backend/optimizer/util/plancat.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -212,8 +212,8 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
212212

213213
info->relam = indexRelation->rd_rel->relam;
214214
info->amcostestimate = indexRelation->rd_am->amcostestimate;
215+
info->canreturn = index_can_return(indexRelation);
215216
info->amcanorderbyop = indexRelation->rd_am->amcanorderbyop;
216-
info->amcanreturn = indexRelation->rd_am->amcanreturn;
217217
info->amoptionalkey = indexRelation->rd_am->amoptionalkey;
218218
info->amsearcharray = indexRelation->rd_am->amsearcharray;
219219
info->amsearchnulls = indexRelation->rd_am->amsearchnulls;

‎src/include/access/genam.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -156,6 +156,7 @@ extern IndexBulkDeleteResult *index_bulk_delete(IndexVacuumInfo *info,
156156
void *callback_state);
157157
extern IndexBulkDeleteResult *index_vacuum_cleanup(IndexVacuumInfo *info,
158158
IndexBulkDeleteResult *stats);
159+
extern bool index_can_return(Relation indexRelation);
159160
extern RegProcedure index_getprocid(Relation irel, AttrNumber attnum,
160161
uint16 procnum);
161162
extern FmgrInfo *index_getprocinfo(Relation irel, AttrNumber attnum,

‎src/include/access/nbtree.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -607,6 +607,7 @@ extern Datum btmarkpos(PG_FUNCTION_ARGS);
607607
extern Datum btrestrpos(PG_FUNCTION_ARGS);
608608
extern Datum btbulkdelete(PG_FUNCTION_ARGS);
609609
extern Datum btvacuumcleanup(PG_FUNCTION_ARGS);
610+
extern Datum btcanreturn(PG_FUNCTION_ARGS);
610611
extern Datum btoptions(PG_FUNCTION_ARGS);
611612

612613
/*

‎src/include/access/spgist.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -182,6 +182,7 @@ extern Datum spgmarkpos(PG_FUNCTION_ARGS);
182182
extern Datum spgrestrpos(PG_FUNCTION_ARGS);
183183
extern Datum spggetbitmap(PG_FUNCTION_ARGS);
184184
extern Datum spggettuple(PG_FUNCTION_ARGS);
185+
extern Datum spgcanreturn(PG_FUNCTION_ARGS);
185186

186187
/* spgutils.c */
187188
extern Datum spgoptions(PG_FUNCTION_ARGS);

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