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Commit0d26812

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Fix handling of empty uncompressed posting list pages in GIN
PostgreSQL 9.4 introduces posting list compression in GIN. This featuresupports online upgrade, so that after pg_upgrade uncompressed postinglists are compressed on-the-fly. Underlying code appears to alwaysexpect at least one item on uncompressed posting list page. But therecould be completely empty pages, because VACUUM never deletes leftmostand rightmost pages from posting trees. This commit fixes that.Reported-by: Sivasubramanian RamasubramanianDiscussion:https://postgr.es/m/1531867212836.63354%40amazon.comAuthor: Sivasubramanian Ramasubramanian, Alexander KorotkovBackpatch-through: 9.4
1 parentff4fb4c commit0d26812

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2 files changed

+33
-14
lines changed

2 files changed

+33
-14
lines changed

‎src/backend/access/gin/gindatapage.c

Lines changed: 12 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -1393,23 +1393,27 @@ disassembleLeaf(Page page)
13931393
{
13941394
/*
13951395
* A pre-9.4 format uncompressed page is represented by a single
1396-
* segment, with an array of items.
1396+
* segment, with an array of items. The corner case is uncompressed
1397+
* page containing no items, which is represented as no segments.
13971398
*/
13981399
ItemPointeruncompressed;
13991400
intnuncompressed;
14001401
leafSegmentInfo*seginfo;
14011402

14021403
uncompressed=dataLeafPageGetUncompressed(page,&nuncompressed);
14031404

1404-
seginfo=palloc(sizeof(leafSegmentInfo));
1405+
if (nuncompressed>0)
1406+
{
1407+
seginfo=palloc(sizeof(leafSegmentInfo));
14051408

1406-
seginfo->action=GIN_SEGMENT_REPLACE;
1407-
seginfo->seg=NULL;
1408-
seginfo->items=palloc(nuncompressed*sizeof(ItemPointerData));
1409-
memcpy(seginfo->items,uncompressed,nuncompressed*sizeof(ItemPointerData));
1410-
seginfo->nitems=nuncompressed;
1409+
seginfo->action=GIN_SEGMENT_REPLACE;
1410+
seginfo->seg=NULL;
1411+
seginfo->items=palloc(nuncompressed*sizeof(ItemPointerData));
1412+
memcpy(seginfo->items,uncompressed,nuncompressed*sizeof(ItemPointerData));
1413+
seginfo->nitems=nuncompressed;
14111414

1412-
dlist_push_tail(&leaf->segments,&seginfo->node);
1415+
dlist_push_tail(&leaf->segments,&seginfo->node);
1416+
}
14131417

14141418
leaf->oldformat= true;
14151419
}

‎src/backend/access/gin/ginxlog.c

Lines changed: 21 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -153,15 +153,30 @@ ginRedoRecompress(Page page, ginxlogRecompressDataLeaf *data)
153153
ItemPointeruncompressed= (ItemPointer)GinDataPageGetData(page);
154154
intnuncompressed=GinPageGetOpaque(page)->maxoff;
155155
intnpacked;
156-
GinPostingList*plist;
157156

158-
plist=ginCompressPostingList(uncompressed,nuncompressed,
159-
BLCKSZ,&npacked);
160-
Assert(npacked==nuncompressed);
157+
/*
158+
* Empty leaf pages are deleted as part of vacuum, but leftmost and
159+
* rightmost pages are never deleted. So, pg_upgrade'd from pre-9.4
160+
* instances might contain empty leaf pages, and we need to handle
161+
* them correctly.
162+
*/
163+
if (nuncompressed>0)
164+
{
165+
GinPostingList*plist;
166+
167+
plist=ginCompressPostingList(uncompressed,nuncompressed,
168+
BLCKSZ,&npacked);
169+
totalsize=SizeOfGinPostingList(plist);
170+
171+
Assert(npacked==nuncompressed);
161172

162-
totalsize=SizeOfGinPostingList(plist);
173+
memcpy(GinDataLeafPageGetPostingList(page),plist,totalsize);
174+
}
175+
else
176+
{
177+
totalsize=0;
178+
}
163179

164-
memcpy(GinDataLeafPageGetPostingList(page),plist,totalsize);
165180
GinDataPageSetDataSize(page,totalsize);
166181
GinPageSetCompressed(page);
167182
GinPageGetOpaque(page)->maxoff=InvalidOffsetNumber;

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