Skip setting up shared instrumentation for Hash node if not needed.

We don't need to set up the shared space for hash join instrumentation data
if instrumentation hasn't been requested.  Let's follow the example of the
similar Sort node code and save a few cycles by skipping that when we can.

This reverts commit d59ff4ab3 and instead allows us to use the safer choice
of passing noError = false to shm_toc_lookup in ExecHashInitializeWorker,
since if we reach that call there should be a TOC entry to be found.

Thomas Munro

Discussion: https://postgr.es/m/E1ehkoZ-0005uW-43%40gemulon.postgresql.org

diff --git a/src/backend/executor/nodeHash.c b/src/backend/executor/nodeHash.c
index 70553b8fdf97ed1aaec2fe510345279fa40bcbef..b10f84745275c212efa977a8b1daeed0a5a4f82e 100644 (file)
--- a/src/backend/executor/nodeHash.c
+++ b/src/backend/executor/nodeHash.c
@@ -2549,6 +2549,10 @@ ExecHashEstimate(HashState *node, ParallelContext *pcxt)
 {
        size_t          size;
 
+       /* don't need this if not instrumenting or no workers */
+       if (!node->ps.instrument || pcxt->nworkers == 0)
+               return;
+
        size = mul_size(pcxt->nworkers, sizeof(HashInstrumentation));
        size = add_size(size, offsetof(SharedHashInfo, hinstrument));
        shm_toc_estimate_chunk(&pcxt->estimator, size);
@@ -2564,6 +2568,10 @@ ExecHashInitializeDSM(HashState *node, ParallelContext *pcxt)
 {
        size_t          size;
 
+       /* don't need this if not instrumenting or no workers */
+       if (!node->ps.instrument || pcxt->nworkers == 0)
+               return;
+
        size = offsetof(SharedHashInfo, hinstrument) +
                pcxt->nworkers * sizeof(HashInstrumentation);
        node->shared_info = (SharedHashInfo *) shm_toc_allocate(pcxt->toc, size);
@@ -2582,13 +2590,13 @@ ExecHashInitializeWorker(HashState *node, ParallelWorkerContext *pwcxt)
 {
        SharedHashInfo *shared_info;
 
-       /* might not be there ... */
+       /* don't need this if not instrumenting */
+       if (!node->ps.instrument)
+               return;
+
        shared_info = (SharedHashInfo *)
-               shm_toc_lookup(pwcxt->toc, node->ps.plan->plan_node_id, true);
-       if (shared_info)
-               node->hinstrument = &shared_info->hinstrument[ParallelWorkerNumber];
-       else
-               node->hinstrument = NULL;
+               shm_toc_lookup(pwcxt->toc, node->ps.plan->plan_node_id, false);
+       node->hinstrument = &shared_info->hinstrument[ParallelWorkerNumber];
 }
 
 /*
@@ -2614,6 +2622,9 @@ ExecHashRetrieveInstrumentation(HashState *node)
        SharedHashInfo *shared_info = node->shared_info;
        size_t          size;
 
+       if (shared_info == NULL)
+               return;
+
        /* Replace node->shared_info with a copy in backend-local memory. */
        size = offsetof(SharedHashInfo, hinstrument) +
                shared_info->num_workers * sizeof(HashInstrumentation);