2 files changed, 33 insertions, 14 deletions

diff --git a/src/backend/access/gin/gindatapage.c b/src/backend/access/gin/gindatapage.c
index aeaf8adab09..9f20513811e 100644
--- a/src/backend/access/gin/gindatapage.c
+++ b/src/backend/access/gin/gindatapage.c
@@ -1394,7 +1394,8 @@ disassembleLeaf(Page page)
 	{
 		/*
 		 * A pre-9.4 format uncompressed page is represented by a single
-		 * segment, with an array of items.
+		 * segment, with an array of items.  The corner case is uncompressed
+		 * page containing no items, which is represented as no segments.
 		 */
 		ItemPointer uncompressed;
 		int			nuncompressed;
@@ -1402,15 +1403,18 @@ disassembleLeaf(Page page)
 
 		uncompressed = dataLeafPageGetUncompressed(page, &nuncompressed);
 
-		seginfo = palloc(sizeof(leafSegmentInfo));
+		if (nuncompressed > 0)
+		{
+			seginfo = palloc(sizeof(leafSegmentInfo));
 
-		seginfo->action = GIN_SEGMENT_REPLACE;
-		seginfo->seg = NULL;
-		seginfo->items = palloc(nuncompressed * sizeof(ItemPointerData));
-		memcpy(seginfo->items, uncompressed, nuncompressed * sizeof(ItemPointerData));
-		seginfo->nitems = nuncompressed;
+			seginfo->action = GIN_SEGMENT_REPLACE;
+			seginfo->seg = NULL;
+			seginfo->items = palloc(nuncompressed * sizeof(ItemPointerData));
+			memcpy(seginfo->items, uncompressed, nuncompressed * sizeof(ItemPointerData));
+			seginfo->nitems = nuncompressed;
 
-		dlist_push_tail(&leaf->segments, &seginfo->node);
+			dlist_push_tail(&leaf->segments, &seginfo->node);
+		}
 
 		leaf->oldformat = true;
 	}
diff --git a/src/backend/access/gin/ginxlog.c b/src/backend/access/gin/ginxlog.c
index a6e321d77e4..7a1e94a1d56 100644
--- a/src/backend/access/gin/ginxlog.c
+++ b/src/backend/access/gin/ginxlog.c
@@ -153,15 +153,30 @@ ginRedoRecompress(Page page, ginxlogRecompressDataLeaf *data)
 		ItemPointer uncompressed = (ItemPointer) GinDataPageGetData(page);
 		int			nuncompressed = GinPageGetOpaque(page)->maxoff;
 		int			npacked;
-		GinPostingList *plist;
 
-		plist = ginCompressPostingList(uncompressed, nuncompressed,
-									   BLCKSZ, &npacked);
-		Assert(npacked == nuncompressed);
+		/*
+		 * Empty leaf pages are deleted as part of vacuum, but leftmost and
+		 * rightmost pages are never deleted.  So, pg_upgrade'd from pre-9.4
+		 * instances might contain empty leaf pages, and we need to handle
+		 * them correctly.
+		 */
+		if (nuncompressed > 0)
+		{
+			GinPostingList *plist;
+
+			plist = ginCompressPostingList(uncompressed, nuncompressed,
+										   BLCKSZ, &npacked);
+			totalsize = SizeOfGinPostingList(plist);
+
+			Assert(npacked == nuncompressed);
 
-		totalsize = SizeOfGinPostingList(plist);
+			memcpy(GinDataLeafPageGetPostingList(page), plist, totalsize);
+		}
+		else
+		{
+			totalsize = 0;
+		}
 
-		memcpy(GinDataLeafPageGetPostingList(page), plist, totalsize);
 		GinDataPageSetDataSize(page, totalsize);
 		GinPageSetCompressed(page);
 		GinPageGetOpaque(page)->maxoff = InvalidOffsetNumber;