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 d59ff4a 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

Author: tglsfdc

src/backend/executor/nodeHash.c

@@ -2549,6 +2549,10 @@ ExecHashEstimate(HashState *node, ParallelContext *pcxt)
 {
 size_tsize;
 
+/* 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_tsize;
 
+/* 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_tsize;
 
+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);