From 2edc5cd493ce3d7834026970e9d3cd00e203f51a Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Tue, 16 Nov 2010 11:02:11 +0200
Subject: [PATCH] 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 ++++------
src/backend/access/gist/gistutil.c | 21 +++++++++++++++++++++
src/backend/access/gist/gistvacuum.c | 2 +-
src/include/access/gist_private.h | 3 ++-
4 files changed, 28 insertions(+), 8 deletions(-)
diff --git a/src/backend/access/gist/gist.c b/src/backend/access/gist/gist.c
index 3054f98c9e8..8c2dbc940f4 100644
--- a/src/backend/access/gist/gist.c
+++ b/src/backend/access/gist/gist.c
@@ -22,8 +22,6 @@
#include "storage/indexfsm.h"
#include "utils/memutils.h"
-const XLogRecPtr XLogRecPtrForTemp = {1, 1};
-
/* Working state for gistbuild and its callback */
typedef struct
{
@@ -132,7 +130,7 @@ gistbuild(PG_FUNCTION_ARGS)
PageSetTLI(page, ThisTimeLineID);
}
else
- PageSetLSN(page, XLogRecPtrForTemp);
+ PageSetLSN(page, GetXLogRecPtrForTemp());
UnlockReleaseBuffer(buffer);
@@ -423,7 +421,7 @@ gistplacetopage(GISTInsertState *state, GISTSTATE *giststate)
{
for (ptr = dist; ptr; ptr = ptr->next)
{
- PageSetLSN(ptr->page, XLogRecPtrForTemp);
+ PageSetLSN(ptr->page, GetXLogRecPtrForTemp());
}
}
@@ -491,7 +489,7 @@ gistplacetopage(GISTInsertState *state, GISTSTATE *giststate)
PageSetTLI(state->stack->page, ThisTimeLineID);
}
else
- PageSetLSN(state->stack->page, XLogRecPtrForTemp);
+ PageSetLSN(state->stack->page, GetXLogRecPtrForTemp());
if (state->stack->blkno == GIST_ROOT_BLKNO)
state->needInsertComplete = false;
@@ -1027,7 +1025,7 @@ gistnewroot(Relation r, Buffer buffer, IndexTuple *itup, int len, ItemPointer ke
PageSetTLI(page, ThisTimeLineID);
}
else
- PageSetLSN(page, XLogRecPtrForTemp);
+ PageSetLSN(page, GetXLogRecPtrForTemp());
END_CRIT_SECTION();
}
diff --git a/src/backend/access/gist/gistutil.c b/src/backend/access/gist/gistutil.c
index 28ab575425e..d488bbb4200 100644
--- a/src/backend/access/gist/gistutil.c
+++ b/src/backend/access/gist/gistutil.c
@@ -677,3 +677,24 @@ gistoptions(PG_FUNCTION_ARGS)
PG_RETURN_BYTEA_P(result);
PG_RETURN_NULL();
}
+
+/*
+ * Temporary GiST indexes are not WAL-logged, but we need LSNs to detect
+ * concurrent page splits anyway. GetXLogRecPtrForTemp() provides a fake
+ * sequence of LSNs for that purpose. Each call generates an LSN that is
+ * greater than any previous value returned by this function in the same
+ * session.
+ */
+XLogRecPtr
+GetXLogRecPtrForTemp(void)
+{
+ static XLogRecPtr counter = {0, 1};
+
+ counter.xrecoff++;
+ if (counter.xrecoff == 0)
+ {
+ counter.xlogid++;
+ counter.xrecoff++;
+ }
+ return counter;
+}
diff --git a/src/backend/access/gist/gistvacuum.c b/src/backend/access/gist/gistvacuum.c
index 0ff5ba840ee..dbe9406ceb8 100644
--- a/src/backend/access/gist/gistvacuum.c
+++ b/src/backend/access/gist/gistvacuum.c
@@ -268,7 +268,7 @@ gistbulkdelete(PG_FUNCTION_ARGS)
pfree(rdata);
}
else
- PageSetLSN(page, XLogRecPtrForTemp);
+ PageSetLSN(page, GetXLogRecPtrForTemp());
END_CRIT_SECTION();
}
diff --git a/src/include/access/gist_private.h b/src/include/access/gist_private.h
index 34cc5d5a8bf..f2dcbfb39b2 100644
--- a/src/include/access/gist_private.h
+++ b/src/include/access/gist_private.h
@@ -87,7 +87,6 @@ typedef struct GISTScanOpaqueData
typedef GISTScanOpaqueData *GISTScanOpaque;
/* XLog stuff */
-extern const XLogRecPtr XLogRecPtrForTemp;
#define XLOG_GIST_PAGE_UPDATE 0x00
#define XLOG_GIST_NEW_ROOT 0x20
@@ -326,6 +325,8 @@ extern void gistMakeUnionKey(GISTSTATE *giststate, int attno,
GISTENTRY *entry2, bool isnull2,
Datum *dst, bool *dstisnull);
+extern XLogRecPtr GetXLogRecPtrForTemp(void);
+
/* gistvacuum.c */
extern Datum gistbulkdelete(PG_FUNCTION_ARGS);
extern Datum gistvacuumcleanup(PG_FUNCTION_ARGS);
--
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