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

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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
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71
src/backend/access/gist/gistget.c
View File

@ -18,6 +18,7 @@
#include "access/relscan.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "lib/pairingheap.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
#include "utils/rel.h"
@ -243,8 +244,6 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem, double *myDistances,
GISTPageOpaque opaque;
OffsetNumber maxoff;
OffsetNumber i;
GISTSearchTreeItem *tmpItem = so->tmpTreeItem;
bool isNew;
MemoryContext oldcxt;
Assert(!GISTSearchItemIsHeap(*pageItem));
@ -275,18 +274,15 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem, double *myDistances,
oldcxt = MemoryContextSwitchTo(so->queueCxt);
/* Create new GISTSearchItem for the right sibling index page */
item = palloc(sizeof(GISTSearchItem));
item->next = NULL;
item = palloc(SizeOfGISTSearchItem(scan->numberOfOrderBys));
item->blkno = opaque->rightlink;
item->data.parentlsn = pageItem->data.parentlsn;
/* Insert it into the queue using same distances as for this page */
tmpItem->head = item;
tmpItem->lastHeap = NULL;
memcpy(tmpItem->distances, myDistances,
memcpy(item->distances, myDistances,
sizeof(double) * scan->numberOfOrderBys);
(void) rb_insert(so->queue, (RBNode *) tmpItem, &isNew);
pairingheap_add(so->queue, &item->phNode);
MemoryContextSwitchTo(oldcxt);
}
@ -348,8 +344,7 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem, double *myDistances,
oldcxt = MemoryContextSwitchTo(so->queueCxt);
/* Create new GISTSearchItem for this item */
item = palloc(sizeof(GISTSearchItem));
item->next = NULL;
item = palloc(SizeOfGISTSearchItem(scan->numberOfOrderBys));
if (GistPageIsLeaf(page))
{
@ -372,12 +367,10 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem, double *myDistances,
}
/* Insert it into the queue using new distance data */
tmpItem->head = item;
tmpItem->lastHeap = GISTSearchItemIsHeap(*item) ? item : NULL;
memcpy(tmpItem->distances, so->distances,
memcpy(item->distances, so->distances,
sizeof(double) * scan->numberOfOrderBys);
(void) rb_insert(so->queue, (RBNode *) tmpItem, &isNew);
pairingheap_add(so->queue, &item->phNode);
MemoryContextSwitchTo(oldcxt);
}
@ -390,44 +383,24 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem, double *myDistances,
* Extract next item (in order) from search queue
*
* Returns a GISTSearchItem or NULL. Caller must pfree item when done with it.
*
* NOTE: on successful return, so->curTreeItem is the GISTSearchTreeItem that
* contained the result item. Callers can use so->curTreeItem->distances as
* the distances value for the item.
*/
static GISTSearchItem *
getNextGISTSearchItem(GISTScanOpaque so)
{
for (;;)
GISTSearchItem *item;
if (!pairingheap_is_empty(so->queue))
{
GISTSearchItem *item;
/* Update curTreeItem if we don't have one */
if (so->curTreeItem == NULL)
{
so->curTreeItem = (GISTSearchTreeItem *) rb_leftmost(so->queue);
/* Done when tree is empty */
if (so->curTreeItem == NULL)
break;
}
item = so->curTreeItem->head;
if (item != NULL)
{
/* Delink item from chain */
so->curTreeItem->head = item->next;
if (item == so->curTreeItem->lastHeap)
so->curTreeItem->lastHeap = NULL;
/* Return item; caller is responsible to pfree it */
return item;
}
/* curTreeItem is exhausted, so remove it from rbtree */
rb_delete(so->queue, (RBNode *) so->curTreeItem);
so->curTreeItem = NULL;
item = (GISTSearchItem *) pairingheap_remove_first(so->queue);
}
else
{
/* Done when both heaps are empty */
item = NULL;
}
return NULL;
/* Return item; caller is responsible to pfree it */
return item;
}
/*
@ -458,7 +431,7 @@ getNextNearest(IndexScanDesc scan)
/* visit an index page, extract its items into queue */
CHECK_FOR_INTERRUPTS();
gistScanPage(scan, item, so->curTreeItem->distances, NULL, NULL);
gistScanPage(scan, item, item->distances, NULL, NULL);
}
pfree(item);
@ -491,7 +464,6 @@ gistgettuple(PG_FUNCTION_ARGS)
pgstat_count_index_scan(scan->indexRelation);
so->firstCall = false;
so->curTreeItem = NULL;
so->curPageData = so->nPageData = 0;
fakeItem.blkno = GIST_ROOT_BLKNO;
@ -534,7 +506,7 @@ gistgettuple(PG_FUNCTION_ARGS)
* this page, we fall out of the inner "do" and loop around to
* return them.
*/
gistScanPage(scan, item, so->curTreeItem->distances, NULL, NULL);
gistScanPage(scan, item, item->distances, NULL, NULL);
pfree(item);
} while (so->nPageData == 0);
@ -560,7 +532,6 @@ gistgetbitmap(PG_FUNCTION_ARGS)
pgstat_count_index_scan(scan->indexRelation);
/* Begin the scan by processing the root page */
so->curTreeItem = NULL;
so->curPageData = so->nPageData = 0;
fakeItem.blkno = GIST_ROOT_BLKNO;
@ -580,7 +551,7 @@ gistgetbitmap(PG_FUNCTION_ARGS)
CHECK_FOR_INTERRUPTS();
gistScanPage(scan, item, so->curTreeItem->distances, tbm, &ntids);
gistScanPage(scan, item, item->distances, tbm, &ntids);
pfree(item);
}

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 */