database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-03 20:02:46 +03:00
Code Activity

Use a pairing heap for the priority queue in kNN-GiST searches.

Browse Source 
This performs slightly better, uses less memory, and needs slightly less
code in GiST, than the Red-Black tree previously used.

Reviewed by Peter Geoghegan
This commit is contained in:
Heikki Linnakangas
2014-12-22 12:05:57 +02:00
parent 699300a146
commit e7032610f7
7 changed files with 409 additions and 134 deletions
Download Patch File Download Diff File Expand all files Collapse all files

75
src/backend/access/gist/gistscan.c
View File

@ -22,14 +22,13 @@
/*
* RBTree support functions for the GISTSearchTreeItem queue
* Pairing heap comparison function for the GISTSearchItem queue
*/
static int
GISTSearchTreeItemComparator(const RBNode *a, const RBNode *b, void *arg)
pairingheap_GISTSearchItem_cmp(const pairingheap_node *a, const pairingheap_node *b, void *arg)
{
const GISTSearchTreeItem *sa = (const GISTSearchTreeItem *) a;
const GISTSearchTreeItem *sb = (const GISTSearchTreeItem *) b;
const GISTSearchItem *sa = (const GISTSearchItem *) a;
const GISTSearchItem *sb = (const GISTSearchItem *) b;
IndexScanDesc scan = (IndexScanDesc) arg;
int i;
@ -37,61 +36,18 @@ GISTSearchTreeItemComparator(const RBNode *a, const RBNode *b, void *arg)
for (i = 0; i < scan->numberOfOrderBys; i++)
{
if (sa->distances[i] != sb->distances[i])
return (sa->distances[i] > sb->distances[i]) ? 1 : -1;
return (sa->distances[i] < sb->distances[i]) ? 1 : -1;
}
/* Heap items go before inner pages, to ensure a depth-first search */
if (GISTSearchItemIsHeap(*sa) && !GISTSearchItemIsHeap(*sb))
return -1;
if (!GISTSearchItemIsHeap(*sa) && GISTSearchItemIsHeap(*sb))
return 1;
return 0;
}
static void
GISTSearchTreeItemCombiner(RBNode *existing, const RBNode *newrb, void *arg)
{
GISTSearchTreeItem *scurrent = (GISTSearchTreeItem *) existing;
const GISTSearchTreeItem *snew = (const GISTSearchTreeItem *) newrb;
GISTSearchItem *newitem = snew->head;
/* snew should have just one item in its chain */
Assert(newitem && newitem->next == NULL);
/*
* If new item is heap tuple, it goes to front of chain; otherwise insert
* it before the first index-page item, so that index pages are visited in
* LIFO order, ensuring depth-first search of index pages. See comments
* in gist_private.h.
*/
if (GISTSearchItemIsHeap(*newitem))
{
newitem->next = scurrent->head;
scurrent->head = newitem;
if (scurrent->lastHeap == NULL)
scurrent->lastHeap = newitem;
}
else if (scurrent->lastHeap == NULL)
{
newitem->next = scurrent->head;
scurrent->head = newitem;
}
else
{
newitem->next = scurrent->lastHeap->next;
scurrent->lastHeap->next = newitem;
}
}
static RBNode *
GISTSearchTreeItemAllocator(void *arg)
{
IndexScanDesc scan = (IndexScanDesc) arg;
return palloc(GSTIHDRSZ + sizeof(double) * scan->numberOfOrderBys);
}
static void
GISTSearchTreeItemDeleter(RBNode *rb, void *arg)
{
pfree(rb);
}
/*
* Index AM API functions for scanning GiST indexes
@ -127,7 +83,6 @@ gistbeginscan(PG_FUNCTION_ARGS)
so->queueCxt = giststate->scanCxt; /* see gistrescan */
/* workspaces with size dependent on numberOfOrderBys: */
so->tmpTreeItem = palloc(GSTIHDRSZ + sizeof(double) * scan->numberOfOrderBys);
so->distances = palloc(sizeof(double) * scan->numberOfOrderBys);
so->qual_ok = true; /* in case there are zero keys */
@ -188,15 +143,9 @@ gistrescan(PG_FUNCTION_ARGS)
/* create new, empty RBTree for search queue */
oldCxt = MemoryContextSwitchTo(so->queueCxt);
so->queue = rb_create(GSTIHDRSZ + sizeof(double) * scan->numberOfOrderBys,
GISTSearchTreeItemComparator,
GISTSearchTreeItemCombiner,
GISTSearchTreeItemAllocator,
GISTSearchTreeItemDeleter,
scan);
so->queue = pairingheap_allocate(pairingheap_GISTSearchItem_cmp, scan);
MemoryContextSwitchTo(oldCxt);
so->curTreeItem = NULL;
so->firstCall = true;
/* Update scan key, if a new one is given */