Fix race conditions associated with SPGiST redirection tuples.

The correct test for whether a redirection tuple is removable is whether
tuple's xid < RecentGlobalXmin, not OldestXmin; the previous coding
failed to protect index searches being done in concurrent transactions that
have no XID.  This mirrors the recent fix in btree's page recycling logic
made in commit d3abbbebe52eb1e59e621c880ad57df9d40d13f2.

Also, WAL-log the newest XID of any removed redirection tuple on an index
page, and apply ResolveRecoveryConflictWithSnapshot during InHotStandby WAL
replay.  This protects against concurrent Hot Standby transactions possibly
needing to see the redirection tuple(s).

Per my query of 2012-03-12 and subsequent discussion.

diff --git a/src/backend/access/spgist/spgutils.c b/src/backend/access/spgist/spgutils.c
index afa14841003505399155a06fd24796f382827796..72aae02b4506b7855848715caab2f66054757d07 100644 (file)
--- a/src/backend/access/spgist/spgutils.c
+++ b/src/backend/access/spgist/spgutils.c
@@ -722,6 +722,7 @@ spgFormDeadTuple(SpGistState *state, int tupstate,
        if (tupstate == SPGIST_REDIRECT)
        {
                ItemPointerSet(&tuple->pointer, blkno, offnum);
+               Assert(TransactionIdIsValid(state->myXid));
                tuple->xid = state->myXid;
        }
        else

diff --git a/src/backend/access/spgist/spgvacuum.c b/src/backend/access/spgist/spgvacuum.c
index 27b55170cb4b3bfa083ce0d7ffa7cbbb1d1f2733..26bbd656c100ee96d530fdc3d0d93f28be094af4 100644 (file)
--- a/src/backend/access/spgist/spgvacuum.c
+++ b/src/backend/access/spgist/spgvacuum.c
@@ -24,7 +24,6 @@
 #include "storage/bufmgr.h"
 #include "storage/indexfsm.h"
 #include "storage/lmgr.h"
-#include "storage/procarray.h"
 #include "utils/snapmgr.h"
 
 
@@ -49,7 +48,6 @@ typedef struct spgBulkDeleteState
        SpGistState spgstate;           /* for SPGiST operations that need one */
        spgVacPendingItem *pendingList;         /* TIDs we need to (re)visit */
        TransactionId myXmin;           /* for detecting newly-added redirects */
-       TransactionId OldestXmin;       /* for deciding a redirect is obsolete */
        BlockNumber lastFilledBlock;    /* last non-deletable block */
 } spgBulkDeleteState;
 
@@ -491,8 +489,7 @@ vacuumLeafRoot(spgBulkDeleteState *bds, Relation index, Buffer buffer)
  * Unlike the routines above, this works on both leaf and inner pages.
  */
 static void
-vacuumRedirectAndPlaceholder(Relation index, Buffer buffer,
-                                                        TransactionId OldestXmin)
+vacuumRedirectAndPlaceholder(Relation index, Buffer buffer)
 {
        Page            page = BufferGetPage(buffer);
        SpGistPageOpaque opaque = SpGistPageGetOpaque(page);
@@ -509,6 +506,7 @@ vacuumRedirectAndPlaceholder(Relation index, Buffer buffer,
        xlrec.node = index->rd_node;
        xlrec.blkno = BufferGetBlockNumber(buffer);
        xlrec.nToPlaceholder = 0;
+       xlrec.newestRedirectXid = InvalidTransactionId;
 
        START_CRIT_SECTION();
 
@@ -526,13 +524,18 @@ vacuumRedirectAndPlaceholder(Relation index, Buffer buffer,
                dt = (SpGistDeadTuple) PageGetItem(page, PageGetItemId(page, i));
 
                if (dt->tupstate == SPGIST_REDIRECT &&
-                       TransactionIdPrecedes(dt->xid, OldestXmin))
+                       TransactionIdPrecedes(dt->xid, RecentGlobalXmin))
                {
                        dt->tupstate = SPGIST_PLACEHOLDER;
                        Assert(opaque->nRedirection > 0);
                        opaque->nRedirection--;
                        opaque->nPlaceholder++;
 
+                       /* remember newest XID among the removed redirects */
+                       if (!TransactionIdIsValid(xlrec.newestRedirectXid) ||
+                               TransactionIdPrecedes(xlrec.newestRedirectXid, dt->xid))
+                               xlrec.newestRedirectXid = dt->xid;
+
                        ItemPointerSetInvalid(&dt->pointer);
 
                        itemToPlaceholder[xlrec.nToPlaceholder] = i;
@@ -640,13 +643,13 @@ spgvacuumpage(spgBulkDeleteState *bds, BlockNumber blkno)
                else
                {
                        vacuumLeafPage(bds, index, buffer, false);
-                       vacuumRedirectAndPlaceholder(index, buffer, bds->OldestXmin);
+                       vacuumRedirectAndPlaceholder(index, buffer);
                }
        }
        else
        {
                /* inner page */
-               vacuumRedirectAndPlaceholder(index, buffer, bds->OldestXmin);
+               vacuumRedirectAndPlaceholder(index, buffer);
        }
 
        /*
@@ -723,7 +726,7 @@ spgprocesspending(spgBulkDeleteState *bds)
                        /* deal with any deletable tuples */
                        vacuumLeafPage(bds, index, buffer, true);
                        /* might as well do this while we are here */
-                       vacuumRedirectAndPlaceholder(index, buffer, bds->OldestXmin);
+                       vacuumRedirectAndPlaceholder(index, buffer);
 
                        SpGistSetLastUsedPage(index, buffer);
 
@@ -806,7 +809,6 @@ spgvacuumscan(spgBulkDeleteState *bds)
        initSpGistState(&bds->spgstate, index);
        bds->pendingList = NULL;
        bds->myXmin = GetActiveSnapshot()->xmin;
-       bds->OldestXmin = GetOldestXmin(true, false);
        bds->lastFilledBlock = SPGIST_LAST_FIXED_BLKNO;
 
        /*

diff --git a/src/backend/access/spgist/spgxlog.c b/src/backend/access/spgist/spgxlog.c
index 82f8c8b978a01a426d4019aa5f7fdbfc463a5b36..45eda70ac765bdb39cba76d35127784c76821716 100644 (file)
--- a/src/backend/access/spgist/spgxlog.c
+++ b/src/backend/access/spgist/spgxlog.c
@@ -15,8 +15,9 @@
 #include "postgres.h"
 
 #include "access/spgist_private.h"
+#include "access/transam.h"
 #include "access/xlogutils.h"
-#include "storage/bufmgr.h"
+#include "storage/standby.h"
 #include "utils/memutils.h"
 
 
@@ -888,6 +889,15 @@ spgRedoVacuumRedirect(XLogRecPtr lsn, XLogRecord *record)
        ptr += sizeof(spgxlogVacuumRedirect);
        itemToPlaceholder = (OffsetNumber *) ptr;
 
+       /*
+        * If any redirection tuples are being removed, make sure there are no
+        * live Hot Standby transactions that might need to see them.  This code
+        * behaves similarly to btree's XLOG_BTREE_REUSE_PAGE case.
+        */
+       if (InHotStandby && TransactionIdIsValid(xldata->newestRedirectXid))
+               ResolveRecoveryConflictWithSnapshot(xldata->newestRedirectXid,
+                                                                                       xldata->node);
+
        if (!(record->xl_info & XLR_BKP_BLOCK_1))
        {
                buffer = XLogReadBuffer(xldata->node, xldata->blkno, false);
@@ -1060,8 +1070,9 @@ spg_desc(StringInfo buf, uint8 xl_info, char *rec)
                        break;
                case XLOG_SPGIST_VACUUM_REDIRECT:
                        out_target(buf, ((spgxlogVacuumRedirect *) rec)->node);
-                       appendStringInfo(buf, "vacuum redirect tuples on page %u",
-                                                        ((spgxlogVacuumRedirect *) rec)->blkno);
+                       appendStringInfo(buf, "vacuum redirect tuples on page %u, newest XID %u",
+                                                        ((spgxlogVacuumRedirect *) rec)->blkno,
+                                                        ((spgxlogVacuumRedirect *) rec)->newestRedirectXid);
                        break;
                default:
                        appendStringInfo(buf, "unknown spgist op code %u", info);

diff --git a/src/include/access/spgist_private.h b/src/include/access/spgist_private.h
index 74267a439002af2bc58806b0898a02098c2b5465..b5bc45121aa8a84cf30609aa9302897b447f5625 100644 (file)
--- a/src/include/access/spgist_private.h
+++ b/src/include/access/spgist_private.h
@@ -591,6 +591,7 @@ typedef struct spgxlogVacuumRedirect
        BlockNumber blkno;                      /* block number to clean */
        uint16          nToPlaceholder; /* number of redirects to make placeholders */
        OffsetNumber firstPlaceholder;          /* first placeholder tuple to remove */
+       TransactionId newestRedirectXid;        /* newest XID of removed redirects */
 
        /* offsets of redirect tuples to make placeholders follow */
 } spgxlogVacuumRedirect;