Fix EXPLAIN ANALYZE of hash join when the leader doesn't participate.

If a hash join appears in a parallel query, there may be no hash table
available for explain.c to inspect even though a hash table may have
been built in other processes.  This could happen either because
parallel_leader_participation was set to off or because the leader
happened to hit the end of the outer relation immediately (even though
the complete relation is not empty) and decided not to build the hash
table.

Commit bf11e7ee introduced a way for workers to exchange
instrumentation via the DSM segment for Sort nodes even though they
are not parallel-aware.  This commit does the same for Hash nodes, so
that explain.c has a way to find instrumentation data from an
arbitrary participant that actually built the hash table.

Author: Thomas Munro
Reviewed-By: Andres Freund
Discussion: https://postgr.es/m/CAEepm%3D3DUQC2-z252N55eOcZBer6DPdM%3DFzrxH9dZc5vYLsjaA%40mail.gmail.com

1 files changed, 33 insertions, 10 deletions

diff --git a/src/backend/executor/execParallel.c b/src/backend/executor/execParallel.c
index 53c5254be13..0aca00b0e68 100644
--- a/src/backend/executor/execParallel.c
+++ b/src/backend/executor/execParallel.c
@@ -29,6 +29,7 @@
 #include "executor/nodeBitmapHeapscan.h"
 #include "executor/nodeCustom.h"
 #include "executor/nodeForeignscan.h"
+#include "executor/nodeHash.h"
 #include "executor/nodeIndexscan.h"
 #include "executor/nodeIndexonlyscan.h"
 #include "executor/nodeSeqscan.h"
@@ -259,8 +260,12 @@ ExecParallelEstimate(PlanState *planstate, ExecParallelEstimateContext *e)
 				ExecBitmapHeapEstimate((BitmapHeapScanState *) planstate,
 									   e->pcxt);
 			break;
+		case T_HashState:
+			/* even when not parallel-aware, for EXPLAIN ANALYZE */
+			ExecHashEstimate((HashState *) planstate, e->pcxt);
+			break;
 		case T_SortState:
-			/* even when not parallel-aware */
+			/* even when not parallel-aware, for EXPLAIN ANALYZE */
 			ExecSortEstimate((SortState *) planstate, e->pcxt);
 			break;
 
@@ -458,8 +463,12 @@ ExecParallelInitializeDSM(PlanState *planstate,
 				ExecBitmapHeapInitializeDSM((BitmapHeapScanState *) planstate,
 											d->pcxt);
 			break;
+		case T_HashState:
+			/* even when not parallel-aware, for EXPLAIN ANALYZE */
+			ExecHashInitializeDSM((HashState *) planstate, d->pcxt);
+			break;
 		case T_SortState:
-			/* even when not parallel-aware */
+			/* even when not parallel-aware, for EXPLAIN ANALYZE */
 			ExecSortInitializeDSM((SortState *) planstate, d->pcxt);
 			break;
 
@@ -872,8 +881,12 @@ ExecParallelReInitializeDSM(PlanState *planstate,
 				ExecBitmapHeapReInitializeDSM((BitmapHeapScanState *) planstate,
 											  pcxt);
 			break;
+		case T_HashState:
+			/* even when not parallel-aware, for EXPLAIN ANALYZE */
+			ExecHashReInitializeDSM((HashState *) planstate, pcxt);
+			break;
 		case T_SortState:
-			/* even when not parallel-aware */
+			/* even when not parallel-aware, for EXPLAIN ANALYZE */
 			ExecSortReInitializeDSM((SortState *) planstate, pcxt);
 			break;
 
@@ -928,12 +941,18 @@ ExecParallelRetrieveInstrumentation(PlanState *planstate,
 	planstate->worker_instrument->num_workers = instrumentation->num_workers;
 	memcpy(&planstate->worker_instrument->instrument, instrument, ibytes);
 
-	/*
-	 * Perform any node-type-specific work that needs to be done.  Currently,
-	 * only Sort nodes need to do anything here.
-	 */
-	if (IsA(planstate, SortState))
-		ExecSortRetrieveInstrumentation((SortState *) planstate);
+	/* Perform any node-type-specific work that needs to be done. */
+	switch (nodeTag(planstate))
+	{
+		case T_SortState:
+			ExecSortRetrieveInstrumentation((SortState *) planstate);
+			break;
+		case T_HashState:
+			ExecHashRetrieveInstrumentation((HashState *) planstate);
+			break;
+		default:
+			break;
+	}
 
 	return planstate_tree_walker(planstate, ExecParallelRetrieveInstrumentation,
 								 instrumentation);
@@ -1160,8 +1179,12 @@ ExecParallelInitializeWorker(PlanState *planstate, ParallelWorkerContext *pwcxt)
 				ExecBitmapHeapInitializeWorker((BitmapHeapScanState *) planstate,
 											   pwcxt);
 			break;
+		case T_HashState:
+			/* even when not parallel-aware, for EXPLAIN ANALYZE */
+			ExecHashInitializeWorker((HashState *) planstate, pwcxt);
+			break;
 		case T_SortState:
-			/* even when not parallel-aware */
+			/* even when not parallel-aware, for EXPLAIN ANALYZE */
 			ExecSortInitializeWorker((SortState *) planstate, pwcxt);
 			break;