Fix GiST buffering build bug, which caused "failed to re-find parent" errors.

We use a hash table to track the parents of inner pages, but when inserting
to a leaf page, the caller of gistbufferinginserttuples() must pass a
correct block number of the leaf's parent page. Before gistProcessItup()
descends to a child page, it checks if the downlink needs to be adjusted to
accommodate the new tuple, and updates the downlink if necessary. However,
updating the downlink might require splitting the page, which might move the
downlink to a page to the right. gistProcessItup() doesn't realize that, so
when it descends to the leaf page, it might pass an out-of-date parent block
number as a result. Fix that by returning the block a tuple was inserted to
from gistbufferinginserttuples().

This fixes the bug reported by Zdeněk Jílovec.

src/backend/access/gist/gist.c

@@ -148,16 +148,22 @@ gistinsert(PG_FUNCTION_ARGS)
  * pages are released; note that new tuple(s) are *not* on the root page
  * but in one of the new child pages.
  *
+ * If 'newblkno' is not NULL, returns the block number of page the first
+ * new/updated tuple was inserted to. Usually it's the given page, but could
+ * be its right sibling if the page was split.
+ *
  * Returns 'true' if the page was split, 'false' otherwise.
  */
 bool
 gistplacetopage(Relation rel, Size freespace, GISTSTATE *giststate,
 				Buffer buffer,
 				IndexTuple *itup, int ntup, OffsetNumber oldoffnum,
+				BlockNumber *newblkno,
 				Buffer leftchildbuf,
 				List **splitinfo,
 				bool markfollowright)
 {
+	BlockNumber blkno = BufferGetBlockNumber(buffer);
 	Page		page = BufferGetPage(buffer);
 	bool		is_leaf = (GistPageIsLeaf(page)) ? true : false;
 	XLogRecPtr	recptr;
@@ -199,7 +205,6 @@ gistplacetopage(Relation rel, Size freespace, GISTSTATE *giststate,
 		BlockNumber oldrlink = InvalidBlockNumber;
 		GistNSN		oldnsn = 0;
 		SplitedPageLayout rootpg;
-		BlockNumber blkno = BufferGetBlockNumber(buffer);
 		bool		is_rootsplit;
 
 		is_rootsplit = (blkno == GIST_ROOT_BLKNO);
@@ -319,9 +324,19 @@ gistplacetopage(Relation rel, Size freespace, GISTSTATE *giststate,
 
 			for (i = 0; i < ptr->block.num; i++)
 			{
-				if (PageAddItem(ptr->page, (Item) data, IndexTupleSize((IndexTuple) data), i + FirstOffsetNumber, false, false) == InvalidOffsetNumber)
+				IndexTuple	thistup = (IndexTuple) data;
+
+				if (PageAddItem(ptr->page, (Item) data, IndexTupleSize(thistup), i + FirstOffsetNumber, false, false) == InvalidOffsetNumber)
 					elog(ERROR, "failed to add item to index page in \"%s\"", RelationGetRelationName(rel));
-				data += IndexTupleSize((IndexTuple) data);
+
+				/*
+				 * If this is the first inserted/updated tuple, let the caller
+				 * know which page it landed on.
+				 */
+				if (newblkno && ItemPointerEquals(&thistup->t_tid, &(*itup)->t_tid))
+					*newblkno = ptr->block.blkno;
+
+				data += IndexTupleSize(thistup);
 			}
 
 			/* Set up rightlinks */
@@ -436,6 +451,9 @@ gistplacetopage(Relation rel, Size freespace, GISTSTATE *giststate,
 			recptr = GetXLogRecPtrForTemp();
 			PageSetLSN(page, recptr);
 		}
+
+		if (newblkno)
+			*newblkno = blkno;
 	}
 
 	/*
@@ -1074,9 +1092,9 @@ gistinserttuple(GISTInsertState *state, GISTInsertStack *stack,
  *	  is kept pinned.
  *	- Lock and pin on 'rightchild' are always released.
  *
- * Returns 'true' if the page had to be split. Note that if the page had
- * be split, the inserted/updated might've been inserted to a right sibling
- * of stack->buffer instead of stack->buffer itself.
+ * Returns 'true' if the page had to be split. Note that if the page was
+ * split, the inserted/updated tuples might've been inserted to a right
+ * sibling of stack->buffer instead of stack->buffer itself.
  */
 static bool
 gistinserttuples(GISTInsertState *state, GISTInsertStack *stack,
@@ -1091,7 +1109,8 @@ gistinserttuples(GISTInsertState *state, GISTInsertStack *stack,
 	/* Insert the tuple(s) to the page, splitting the page if necessary */
 	is_split = gistplacetopage(state->r, state->freespace, giststate,
 							   stack->buffer,
-							   tuples, ntup, oldoffnum,
+							   tuples, ntup,
+							   oldoffnum, NULL,
 							   leftchild,
 							   &splitinfo,
 							   true);

src/backend/access/gist/gistbuild.c

@@ -85,7 +85,7 @@ static void gistBufferingBuildInsert(GISTBuildState *buildstate,
 						 IndexTuple itup);
 static bool gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
 				BlockNumber startblkno, int startlevel);
-static void gistbufferinginserttuples(GISTBuildState *buildstate,
+static BlockNumber gistbufferinginserttuples(GISTBuildState *buildstate,
 						  Buffer buffer, int level,
 						  IndexTuple *itup, int ntup, OffsetNumber oldoffnum,
 						  BlockNumber parentblk, OffsetNumber downlinkoffnum);
@@ -621,7 +621,7 @@ gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
 		newtup = gistgetadjusted(indexrel, idxtuple, itup, giststate);
 		if (newtup)
 		{
-			gistbufferinginserttuples(buildstate, buffer, level,
+			blkno  = gistbufferinginserttuples(buildstate, buffer, level,
 											   &newtup, 1, childoffnum,
 									  InvalidBlockNumber, InvalidOffsetNumber);
 			/* gistbufferinginserttuples() released the buffer */
@@ -676,10 +676,14 @@ gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
  *
  * This is analogous with gistinserttuples() in the regular insertion code.
  *
+ * Returns the block number of the page where the (first) new or updated tuple
+ * was inserted. Usually that's the original page, but might be a sibling page
+ * if the original page was split.
+ *
  * Caller should hold a lock on 'buffer' on entry. This function will unlock
  * and unpin it.
  */
-static void
+static BlockNumber
 gistbufferinginserttuples(GISTBuildState *buildstate, Buffer buffer, int level,
 						  IndexTuple *itup, int ntup, OffsetNumber oldoffnum,
 						  BlockNumber parentblk, OffsetNumber downlinkoffnum)
@@ -687,12 +691,13 @@ gistbufferinginserttuples(GISTBuildState *buildstate, Buffer buffer, int level,
 	GISTBuildBuffers *gfbb = buildstate->gfbb;
 	List	   *splitinfo;
 	bool		is_split;
+	BlockNumber	placed_to_blk = InvalidBlockNumber;
 
 	is_split = gistplacetopage(buildstate->indexrel,
 							   buildstate->freespace,
 							   buildstate->giststate,
 							   buffer,
-							   itup, ntup, oldoffnum,
+							   itup, ntup, oldoffnum, &placed_to_blk,
 							   InvalidBuffer,
 							   &splitinfo,
 							   false);
@@ -823,6 +828,8 @@ gistbufferinginserttuples(GISTBuildState *buildstate, Buffer buffer, int level,
 	}
 	else
 		UnlockReleaseBuffer(buffer);
+
+	return placed_to_blk;
 }
 
 /*

src/include/access/gist_private.h

@@ -430,7 +430,8 @@ typedef struct
 
 extern bool gistplacetopage(Relation rel, Size freespace, GISTSTATE *giststate,
 				Buffer buffer,
-				IndexTuple *itup, int ntup, OffsetNumber oldoffnum,
+				IndexTuple *itup, int ntup,
+				OffsetNumber oldoffnum, BlockNumber *newblkno,
 				Buffer leftchildbuf,
 				List **splitinfo,
 				bool markleftchild);