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Add support for index-only scans in GiST.

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This adds a new GiST opclass method, 'fetch', which is used to reconstruct
the original Datum from the value stored in the index. Also, the 'canreturn'
index AM interface function gains a new 'attno' argument. That makes it
possible to use index-only scans on a multi-column index where some of the
opclasses support index-only scans but some do not.

This patch adds support in the box and point opclasses. Other opclasses
can added later as follow-on patches (btree_gist would be particularly
interesting).

Anastasia Lubennikova, with additional fixes and modifications by me.
This commit is contained in:
Heikki Linnakangas
2015-03-26 19:12:00 +02:00
parent 8fa393a6d7
commit d04c8ed904
24 changed files with 575 additions and 73 deletions
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18
src/backend/access/gist/gistscan.c
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@ -88,6 +88,13 @@ gistbeginscan(PG_FUNCTION_ARGS)
scan->opaque = so;
/*
* All fields required for index-only scans are null until gistrescan.
* However, we set up scan->xs_itupdesc whether we'll need it or not,
* since that's cheap.
*/
scan->xs_itupdesc = RelationGetDescr(r);
MemoryContextSwitchTo(oldCxt);
PG_RETURN_POINTER(scan);
@ -141,6 +148,17 @@ gistrescan(PG_FUNCTION_ARGS)
first_time = false;
}
/*
* If we're doing an index-only scan, also create a memory context to hold
* the returned tuples.
*/
if (scan->xs_want_itup && so->pageDataCxt == NULL)
so->pageDataCxt = AllocSetContextCreate(so->giststate->scanCxt,
"GiST page data context",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
/* create new, empty RBTree for search queue */
oldCxt = MemoryContextSwitchTo(so->queueCxt);
so->queue = pairingheap_allocate(pairingheap_GISTSearchItem_cmp, scan);