From acbffaa77d0c4846f8749daa45fde507be1e969b Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas
Date: Tue, 16 Nov 2010 11:02:11 +0200
Subject: The GiST scan algorithm uses LSNs to detect concurrent pages splits,
 but temporary indexes are not WAL-logged. We used a constant LSN for
 temporary indexes, on the assumption that we don't need to worry about
 concurrent page splits in temporary indexes because they're only visible to
 the current session. But that assumption is wrong, it's possible to insert
 rows and split pages in the same session, while a scan is in progress. For
 example, by opening a cursor and fetching some rows, and INSERTing new rows
 before fetching some more.

Fix by generating fake increasing LSNs, used in place of real LSNs in
temporary GiST indexes.
---
 src/backend/access/gist/gist.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

(limited to 'src/backend/access/gist/gist.c')

diff --git a/src/backend/access/gist/gist.c b/src/backend/access/gist/gist.c
index 00b1620ab00..fbc828e7832 100644
--- a/src/backend/access/gist/gist.c
+++ b/src/backend/access/gist/gist.c
@@ -23,8 +23,6 @@
 #include "miscadmin.h"
 #include "utils/memutils.h"
 
-const XLogRecPtr XLogRecPtrForTemp = {1, 1};
-
 /* Working state for gistbuild and its callback */
 typedef struct
 {
@@ -127,7 +125,7 @@ gistbuild(PG_FUNCTION_ARGS)
 		END_CRIT_SECTION();
 	}
 	else
-		PageSetLSN(BufferGetPage(buffer), XLogRecPtrForTemp);
+		PageSetLSN(BufferGetPage(buffer), GetXLogRecPtrForTemp());
 	LockBuffer(buffer, GIST_UNLOCK);
 	WriteBuffer(buffer);
 
@@ -356,7 +354,7 @@ gistplacetopage(GISTInsertState *state, GISTSTATE *giststate)
 			ptr = dist;
 			while (ptr)
 			{
-				PageSetLSN(BufferGetPage(ptr->buffer), XLogRecPtrForTemp);
+				PageSetLSN(BufferGetPage(ptr->buffer), GetXLogRecPtrForTemp());
 				ptr = ptr->next;
 			}
 		}
@@ -475,7 +473,7 @@ gistplacetopage(GISTInsertState *state, GISTSTATE *giststate)
 			END_CRIT_SECTION();
 		}
 		else
-			PageSetLSN(state->stack->page, XLogRecPtrForTemp);
+			PageSetLSN(state->stack->page, GetXLogRecPtrForTemp());
 
 		if (state->stack->blkno == GIST_ROOT_BLKNO)
 			state->needInsertComplete = false;
@@ -1206,7 +1204,7 @@ gistnewroot(Relation r, Buffer buffer, IndexTuple *itup, int len, ItemPointer ke
 		END_CRIT_SECTION();
 	}
 	else
-		PageSetLSN(page, XLogRecPtrForTemp);
+		PageSetLSN(page, GetXLogRecPtrForTemp());
 }
 
 void
-- 
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