Teach bitmap heap scan to cope with absence of a DSA.

If we have a plan that uses parallelism but are unable to execute it
using parallelism, for example due to a lack of available DSM
segments, then the EState's es_query_dsa will be NULL.  Parallel
bitmap heap scan needs to fall back to a non-parallel scan in such
cases.

Patch by me, reviewed by Dilip Kumar

Discussion: http://postgr.es/m/CAEepm=0kADK5inNf_KuemjX=HQ=PuTP0DykM--fO5jS5ePVFEA@mail.gmail.com

diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index 221391908c718d09574a7aeff9c2d9df65125f2b..eb5bbb57ef118d962d467a9945992ffb4fbebc51 100644 (file)
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -1051,6 +1051,11 @@ ExecBitmapHeapInitializeDSM(BitmapHeapScanState *node,
 {
        ParallelBitmapHeapState *pstate;
        EState     *estate = node->ss.ps.state;
+       dsa_area   *dsa = node->ss.ps.state->es_query_dsa;
+
+       /* If there's no DSA, there are no workers; initialize nothing. */
+       if (dsa == NULL)
+               return;
 
        pstate = shm_toc_allocate(pcxt->toc, node->pscan_len);
 
@@ -1083,6 +1088,10 @@ ExecBitmapHeapReInitializeDSM(BitmapHeapScanState *node,
        ParallelBitmapHeapState *pstate = node->pstate;
        dsa_area   *dsa = node->ss.ps.state->es_query_dsa;
 
+       /* If there's no DSA, there are no workers; do nothing. */
+       if (dsa == NULL)
+               return;
+
        pstate->state = BM_INITIAL;
 
        if (DsaPointerIsValid(pstate->tbmiterator))
@@ -1108,6 +1117,8 @@ ExecBitmapHeapInitializeWorker(BitmapHeapScanState *node,
        ParallelBitmapHeapState *pstate;
        Snapshot        snapshot;
 
+       Assert(node->ss.ps.state->es_query_dsa != NULL);
+
        pstate = shm_toc_lookup(pwcxt->toc, node->ss.ps.plan->plan_node_id, false);
        node->pstate = pstate;