Don't prematurely free the BufferAccessStrategy in pgstat_heap().

This function continued to use it after heap_endscan() freed it.  In
passing, don't explicit create a strategy here.  Instead, use the one
created by heap_beginscan_strat(), if any.  Back-patch to 9.2, where use
of a BufferAccessStrategy here was introduced.

diff --git a/contrib/pgstattuple/pgstattuple.c b/contrib/pgstattuple/pgstattuple.c
index edc603f6a1b097674f822c5b48facf81e5ab2b12..10077483d3587544d214df9034c672905e9280c0 100644 (file)
--- a/contrib/pgstattuple/pgstattuple.c
+++ b/contrib/pgstattuple/pgstattuple.c
@@ -274,7 +274,6 @@ pgstat_heap(Relation rel, FunctionCallInfo fcinfo)
    BlockNumber tupblock;
    Buffer      buffer;
    pgstattuple_type stat = {0};
-   BufferAccessStrategy bstrategy;
    SnapshotData SnapshotDirty;
 
    /* Disable syncscan because we assume we scan from block zero upwards */
@@ -283,10 +282,6 @@ pgstat_heap(Relation rel, FunctionCallInfo fcinfo)
 
    nblocks = scan->rs_nblocks; /* # blocks to be scanned */
 
-   /* prepare access strategy for this table */
-   bstrategy = GetAccessStrategy(BAS_BULKREAD);
-   scan->rs_strategy = bstrategy;
-
    /* scan the relation */
    while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
    {
@@ -320,26 +315,28 @@ pgstat_heap(Relation rel, FunctionCallInfo fcinfo)
        {
            CHECK_FOR_INTERRUPTS();
 
-           buffer = ReadBufferExtended(rel, MAIN_FORKNUM, block, RBM_NORMAL, bstrategy);
+           buffer = ReadBufferExtended(rel, MAIN_FORKNUM, block,
+                                       RBM_NORMAL, scan->rs_strategy);
            LockBuffer(buffer, BUFFER_LOCK_SHARE);
            stat.free_space += PageGetHeapFreeSpace((Page) BufferGetPage(buffer));
            UnlockReleaseBuffer(buffer);
            block++;
        }
    }
-   heap_endscan(scan);
 
    while (block < nblocks)
    {
        CHECK_FOR_INTERRUPTS();
 
-       buffer = ReadBufferExtended(rel, MAIN_FORKNUM, block, RBM_NORMAL, bstrategy);
+       buffer = ReadBufferExtended(rel, MAIN_FORKNUM, block,
+                                   RBM_NORMAL, scan->rs_strategy);
        LockBuffer(buffer, BUFFER_LOCK_SHARE);
        stat.free_space += PageGetHeapFreeSpace((Page) BufferGetPage(buffer));
        UnlockReleaseBuffer(buffer);
        block++;
    }
 
+   heap_endscan(scan);
    relation_close(rel, AccessShareLock);
 
    stat.table_len = (uint64) nblocks *BLCKSZ;