From 25b1dafab63f465a65c63b26834dc18857f0fa0c Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Wed, 29 Jan 2014 18:23:17 +0200
Subject: [PATCH] Further optimize multi-key GIN searches.
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.
---
src/backend/access/gin/gindatapage.c | 38 +++++++++++++++++++++++++---
src/backend/access/gin/ginget.c | 6 +++--
src/include/access/gin_private.h | 2 +-
3 files changed, 39 insertions(+), 7 deletions(-)
diff --git a/src/backend/access/gin/gindatapage.c b/src/backend/access/gin/gindatapage.c
index 91934f0f900..9a0b8ab1f21 100644
--- a/src/backend/access/gin/gindatapage.c
+++ b/src/backend/access/gin/gindatapage.c
@@ -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;
+
+ /* 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;
+ }
- result = ginPostingListDecodeAllSegments(ptr, len, nitems);
+ if (len > 0)
+ result = ginPostingListDecodeAllSegments(seg, len, nitems);
+ else
+ {
+ result = NULL;
+ *nitems = 0;
+ }
}
else
{
diff --git a/src/backend/access/gin/ginget.c b/src/backend/access/gin/ginget.c
index 40abb3971e2..49e47c6859c 100644
--- a/src/backend/access/gin/ginget.c
+++ b/src/backend/access/gin/ginget.c
@@ -400,6 +400,7 @@ restartScanEntry:
BlockNumber rootPostingTree = GinGetPostingTree(itup);
GinBtreeStack *stack;
Page page;
+ ItemPointerData minItem;
/*
* We should unlock entry page before touching posting tree to
@@ -426,7 +427,8 @@ restartScanEntry:
/*
* Load the first page into memory.
*/
- entry->list = GinDataLeafPageGetItems(page, &entry->nlist);
+ ItemPointerSetMin(&minItem);
+ entry->list = GinDataLeafPageGetItems(page, &entry->nlist, minItem);
entry->predictNumberResult = stack->predictNumber * entry->nlist;
@@ -558,7 +560,7 @@ entryLoadMoreItems(GinState *ginstate, GinScanEntry entry, ItemPointerData advan
continue;
}
- entry->list = GinDataLeafPageGetItems(page, &entry->nlist);
+ entry->list = GinDataLeafPageGetItems(page, &entry->nlist, advancePast);
for (i = 0; i < entry->nlist; i++)
{
diff --git a/src/include/access/gin_private.h b/src/include/access/gin_private.h
index d44d0a9fc91..ea9ae31acc0 100644
--- a/src/include/access/gin_private.h
+++ b/src/include/access/gin_private.h
@@ -692,7 +692,7 @@ extern ItemPointer ginReadTuple(GinState *ginstate, OffsetNumber attnum,
IndexTuple itup, int *nitems);
/* gindatapage.c */
-extern ItemPointer GinDataLeafPageGetItems(Page page, int *nitems);
+extern ItemPointer GinDataLeafPageGetItems(Page page, int *nitems, ItemPointerData advancePast);
extern int GinDataLeafPageGetItemsToTbm(Page page, TIDBitmap *tbm);
extern BlockNumber createPostingTree(Relation index,
ItemPointerData *items, uint32 nitems,
--
GitLab