Augment EXPLAIN output with more details on Hash nodes.

We show the number of buckets, the number of batches (and also the original
number if it has changed), and the peak space used by the hash table.  Minor
executor changes to track peak space used.

1 files changed, 47 insertions, 1 deletions

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 37647e57398..8c9b060e6bd 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994-5, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.199 2010/01/15 22:36:29 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.200 2010/02/01 15:43:35 rhaas Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -20,6 +20,7 @@
 #include "commands/explain.h"
 #include "commands/prepare.h"
 #include "commands/trigger.h"
+#include "executor/hashjoin.h"
 #include "executor/instrument.h"
 #include "optimizer/clauses.h"
 #include "optimizer/planner.h"
@@ -67,6 +68,7 @@ static void show_upper_qual(List *qual, const char *qlabel, Plan *plan,
 				ExplainState *es);
 static void show_sort_keys(Plan *sortplan, ExplainState *es);
 static void show_sort_info(SortState *sortstate, ExplainState *es);
+static void show_hash_info(HashState *hashstate, ExplainState *es);
 static const char *explain_get_index_name(Oid indexId);
 static void ExplainScanTarget(Scan *plan, ExplainState *es);
 static void ExplainMemberNodes(List *plans, PlanState **planstate,
@@ -1052,6 +1054,9 @@ ExplainNode(Plan *plan, PlanState *planstate,
 							"One-Time Filter", plan, es);
 			show_upper_qual(plan->qual, "Filter", plan, es);
 			break;
+		case T_Hash:
+			show_hash_info((HashState *) planstate, es);
+			break;
 		default:
 			break;
 	}
@@ -1405,6 +1410,47 @@ show_sort_info(SortState *sortstate, ExplainState *es)
 }
 
 /*
+ * Show information on hash buckets/batches.
+ */
+static void
+show_hash_info(HashState *hashstate, ExplainState *es)
+{
+	HashJoinTable hashtable;
+
+	Assert(IsA(hashstate, HashState));
+	hashtable = hashstate->hashtable;
+
+	if (hashtable)
+	{
+		long spacePeakKb = (hashtable->spacePeak + 1023) / 1024;
+		if (es->format != EXPLAIN_FORMAT_TEXT)
+		{
+			ExplainPropertyLong("Hash Buckets", hashtable->nbuckets, es);
+			ExplainPropertyLong("Hash Batches", hashtable->nbatch, es);
+			ExplainPropertyLong("Original Hash Batches",
+								hashtable->nbatch_original, es);
+			ExplainPropertyLong("Peak Memory Usage", spacePeakKb, es);
+		}
+		else if (hashtable->nbatch_original != hashtable->nbatch)
+		{
+			appendStringInfoSpaces(es->str, es->indent * 2);
+			appendStringInfo(es->str,
+							 "Buckets: %d  Batches: %d (originally %d)  Memory Usage: %ldkB\n",
+							 hashtable->nbuckets, hashtable->nbatch,
+							 hashtable->nbatch_original, spacePeakKb);
+		}
+		else
+		{
+			appendStringInfoSpaces(es->str, es->indent * 2);
+			appendStringInfo(es->str,
+							 "Buckets: %d  Batches: %d  Memory Usage: %ldkB\n",
+							 hashtable->nbuckets, hashtable->nbatch,
+							 spacePeakKb);
+		}
+	}
+}
+
+/*
  * Fetch the name of an index in an EXPLAIN
  *
  * We allow plugins to get control here so that plans involving hypothetical