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Further optimize multi-key GIN searches.

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If we're skipping past a certain TID, avoid decoding posting list segments
that only contain smaller TIDs.

Extracted from Alexander Korotkov's fast scan patch, heavily modified.
This commit is contained in:
Heikki Linnakangas
2014-01-29 18:23:17 +02:00
parent e20c70cb0f
commit 25b1dafab6
3 changed files with 39 additions and 7 deletions
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38
src/backend/access/gin/gindatapage.c
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@@ -96,19 +96,49 @@ static void dataPlaceToPageLeafSplit(Buffer buf,
XLogRecData **prdata, Page lpage, Page rpage);
/*
* Read all TIDs from leaf data page to single uncompressed array.
* Read TIDs from leaf data page to single uncompressed array. The TIDs are
* returned in ascending order.
*
* advancePast is a hint, indicating that the caller is only interested in
* TIDs > advancePast. To return all items, use ItemPointerSetMin.
*
* Note: This function can still return items smaller than advancePast that
* are in the same posting list as the items of interest, so the caller must
* still check all the returned items. But passing it allows this function to
* skip whole posting lists.
*/
ItemPointer
GinDataLeafPageGetItems(Page page, int *nitems)
GinDataLeafPageGetItems(Page page, int *nitems, ItemPointerData advancePast)
{
ItemPointer result;
if (GinPageIsCompressed(page))
{
GinPostingList *ptr = GinDataLeafPageGetPostingList(page);
GinPostingList *seg = GinDataLeafPageGetPostingList(page);
Size len = GinDataLeafPageGetPostingListSize(page);
Pointer endptr = ((Pointer) seg) + len;
GinPostingList *next;
result = ginPostingListDecodeAllSegments(ptr, len, nitems);
/* Skip to the segment containing advancePast+1 */
if (ItemPointerIsValid(&advancePast))
{
next = GinNextPostingListSegment(seg);
while ((Pointer) next < endptr &&
ginCompareItemPointers(&next->first, &advancePast) <= 0)
{
seg = next;
next = GinNextPostingListSegment(seg);
}
len = endptr - (Pointer) seg;
}
if (len > 0)
result = ginPostingListDecodeAllSegments(seg, len, nitems);
else
{
result = NULL;
*nitems = 0;
}
}
else
{