From bdee4af8e07648008fe522fc5a562db453be5ad7 Mon Sep 17 00:00:00 2001
From: David Rowley <drowley@postgresql.org>
Date: Fri, 19 Jun 2020 17:25:07 +1200
Subject: Fix EXPLAIN ANALYZE for parallel HashAgg plans

Since 1f39bce02, HashAgg nodes have had the ability to spill to disk when
memory consumption exceeds work_mem. That commit added new properties to
EXPLAIN ANALYZE to show the maximum memory usage and disk usage, however,
it didn't quite go as far as showing that information for parallel
workers.  Since workers may have experienced something very different from
the main process, we should show this information per worker, as is done
in Sort.

Reviewed-by: Justin Pryzby
Reviewed-by: Jeff Davis
Discussion: https://postgr.es/m/CAApHDvpEKbfZa18mM1TD7qV6PG+w97pwCWq5tVD0dX7e11gRJw@mail.gmail.com
Backpatch-through: 13, where the hashagg spilling code was added.
---
 src/backend/commands/explain.c | 110 +++++++++++++++++++++++++++++++++++------
 1 file changed, 96 insertions(+), 14 deletions(-)

(limited to 'src/backend/commands/explain.c')

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 9092b4b3094..67bdcb2b278 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -3051,29 +3051,111 @@ show_hashagg_info(AggState *aggstate, ExplainState *es)
 	Agg		   *agg = (Agg *) aggstate->ss.ps.plan;
 	int64		memPeakKb = (aggstate->hash_mem_peak + 1023) / 1024;
 
-	Assert(IsA(aggstate, AggState));
-
 	if (agg->aggstrategy != AGG_HASHED &&
 		agg->aggstrategy != AGG_MIXED)
 		return;
 
-	if (es->costs && aggstate->hash_planned_partitions > 0)
+	if (es->format != EXPLAIN_FORMAT_TEXT)
 	{
-		ExplainPropertyInteger("Planned Partitions", NULL,
-							   aggstate->hash_planned_partitions, es);
+
+		if (es->costs && aggstate->hash_planned_partitions > 0)
+		{
+			ExplainPropertyInteger("Planned Partitions", NULL,
+								   aggstate->hash_planned_partitions, es);
+		}
+
+		if (!es->analyze)
+			return;
+
+		/* EXPLAIN ANALYZE */
+		ExplainPropertyInteger("Peak Memory Usage", "kB", memPeakKb, es);
+		if (aggstate->hash_batches_used > 0)
+		{
+			ExplainPropertyInteger("Disk Usage", "kB",
+								   aggstate->hash_disk_used, es);
+			ExplainPropertyInteger("HashAgg Batches", NULL,
+								   aggstate->hash_batches_used, es);
+		}
 	}
+	else
+	{
+		bool		gotone = false;
 
-	if (!es->analyze)
-		return;
+		if (es->costs && aggstate->hash_planned_partitions > 0)
+		{
+			ExplainIndentText(es);
+			appendStringInfo(es->str, "Planned Partitions: %d",
+							 aggstate->hash_planned_partitions);
+			gotone = true;
+		}
+
+		if (!es->analyze)
+		{
+			if (gotone)
+				appendStringInfoChar(es->str, '\n');
+			return;
+		}
+
+		if (!gotone)
+			ExplainIndentText(es);
+		else
+			appendStringInfoString(es->str, "  ");
+
+		appendStringInfo(es->str, "Peak Memory Usage: " INT64_FORMAT " kB",
+						 memPeakKb);
 
-	/* EXPLAIN ANALYZE */
-	ExplainPropertyInteger("Peak Memory Usage", "kB", memPeakKb, es);
-	if (aggstate->hash_batches_used > 0)
+		if (aggstate->hash_batches_used > 0)
+			appendStringInfo(es->str, "  Disk Usage: " UINT64_FORMAT " kB  HashAgg Batches: %d",
+							 aggstate->hash_disk_used,
+							 aggstate->hash_batches_used);
+		appendStringInfoChar(es->str, '\n');
+	}
+
+	/* Display stats for each parallel worker */
+	if (es->analyze && aggstate->shared_info != NULL)
 	{
-		ExplainPropertyInteger("Disk Usage", "kB",
-							   aggstate->hash_disk_used, es);
-		ExplainPropertyInteger("HashAgg Batches", NULL,
-							   aggstate->hash_batches_used, es);
+		for (int n = 0; n < aggstate->shared_info->num_workers; n++)
+		{
+			AggregateInstrumentation *sinstrument;
+			uint64		hash_disk_used;
+			int			hash_batches_used;
+
+			sinstrument = &aggstate->shared_info->sinstrument[n];
+			hash_disk_used = sinstrument->hash_disk_used;
+			hash_batches_used = sinstrument->hash_batches_used;
+			memPeakKb = (sinstrument->hash_mem_peak + 1023) / 1024;
+
+			if (es->workers_state)
+				ExplainOpenWorker(n, es);
+
+			if (es->format == EXPLAIN_FORMAT_TEXT)
+			{
+				ExplainIndentText(es);
+
+				appendStringInfo(es->str, "Peak Memory Usage: " INT64_FORMAT " kB",
+								 memPeakKb);
+
+				if (hash_batches_used > 0)
+					appendStringInfo(es->str, "  Disk Usage: " UINT64_FORMAT " kB  HashAgg Batches: %d",
+									 hash_disk_used, hash_batches_used);
+				appendStringInfoChar(es->str, '\n');
+			}
+			else
+			{
+				ExplainPropertyInteger("Peak Memory Usage", "kB", memPeakKb,
+									   es);
+				if (hash_batches_used > 0)
+				{
+					ExplainPropertyInteger("Disk Usage", "kB", hash_disk_used,
+										   es);
+					ExplainPropertyInteger("HashAgg Batches", NULL,
+										   hash_batches_used, es);
+				}
+			}
+
+			if (es->workers_state)
+				ExplainCloseWorker(n, es);
+		}
 	}
 }
 
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