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.

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;
 	}
@@ -1404,6 +1409,47 @@ 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
  *

src/backend/executor/nodeHash.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeHash.c,v 1.126 2010/01/04 02:44:39 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeHash.c,v 1.127 2010/02/01 15:43:36 rhaas Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -287,6 +287,7 @@ ExecHashTableCreate(Hash *node, List *hashOperators)
 	hashtable->innerBatchFile = NULL;
 	hashtable->outerBatchFile = NULL;
 	hashtable->spaceUsed = 0;
+	hashtable->spacePeak = 0;
 	hashtable->spaceAllowed = work_mem * 1024L;
 	hashtable->spaceUsedSkew = 0;
 	hashtable->spaceAllowedSkew =
@@ -719,6 +720,8 @@ ExecHashTableInsert(HashJoinTable hashtable,
 		hashTuple->next = hashtable->buckets[bucketno];
 		hashtable->buckets[bucketno] = hashTuple;
 		hashtable->spaceUsed += hashTupleSize;
+		if (hashtable->spaceUsed > hashtable->spacePeak)
+			hashtable->spacePeak = hashtable->spaceUsed;
 		if (hashtable->spaceUsed > hashtable->spaceAllowed)
 			ExecHashIncreaseNumBatches(hashtable);
 	}
@@ -1071,6 +1074,8 @@ ExecHashBuildSkewHash(HashJoinTable hashtable, Hash *node, int mcvsToUse)
 			+ mcvsToUse * sizeof(int);
 		hashtable->spaceUsedSkew += nbuckets * sizeof(HashSkewBucket *)
 			+ mcvsToUse * sizeof(int);
+		if (hashtable->spaceUsed > hashtable->spacePeak)
+			hashtable->spacePeak = hashtable->spaceUsed;
 
 		/*
 		 * Create a skew bucket for each MCV hash value.
@@ -1119,6 +1124,8 @@ ExecHashBuildSkewHash(HashJoinTable hashtable, Hash *node, int mcvsToUse)
 			hashtable->nSkewBuckets++;
 			hashtable->spaceUsed += SKEW_BUCKET_OVERHEAD;
 			hashtable->spaceUsedSkew += SKEW_BUCKET_OVERHEAD;
+			if (hashtable->spaceUsed > hashtable->spacePeak)
+				hashtable->spacePeak = hashtable->spaceUsed;
 		}
 
 		free_attstatsslot(node->skewColType,
@@ -1205,6 +1212,8 @@ ExecHashSkewTableInsert(HashJoinTable hashtable,
 	/* Account for space used, and back off if we've used too much */
 	hashtable->spaceUsed += hashTupleSize;
 	hashtable->spaceUsedSkew += hashTupleSize;
+	if (hashtable->spaceUsed > hashtable->spacePeak)
+		hashtable->spacePeak = hashtable->spaceUsed;
 	while (hashtable->spaceUsedSkew > hashtable->spaceAllowedSkew)
 		ExecHashRemoveNextSkewBucket(hashtable);
 

src/include/executor/hashjoin.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/executor/hashjoin.h,v 1.52 2010/01/02 16:58:03 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/executor/hashjoin.h,v 1.53 2010/02/01 15:43:36 rhaas Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -149,6 +149,7 @@ typedef struct HashJoinTableData
 
 	Size		spaceUsed;		/* memory space currently used by tuples */
 	Size		spaceAllowed;	/* upper limit for space used */
+	Size		spacePeak;		/* peak space used */
 	Size		spaceUsedSkew;	/* skew hash table's current space usage */
 	Size		spaceAllowedSkew;		/* upper limit for skew hashtable */