From 7e59c0889ffd7553e8e6c8572603ebb32b1fb649 Mon Sep 17 00:00:00 2001
From: Tomas Vondra <tomas.vondra@postgresql.org>
Date: Sat, 29 Oct 2022 17:46:51 +0200
Subject: [PATCH 02/10] wip: introduce debug_brin_stats

---
 src/backend/access/brin/brin_minmax.c | 80 +++++++++++++++++++++++++++
 src/backend/utils/misc/guc_tables.c   | 18 ++++++
 2 files changed, 98 insertions(+)

diff --git a/src/backend/access/brin/brin_minmax.c b/src/backend/access/brin/brin_minmax.c
index 67e68a8b8ed..6e20a34fbcd 100644
--- a/src/backend/access/brin/brin_minmax.c
+++ b/src/backend/access/brin/brin_minmax.c
@@ -27,6 +27,10 @@
 #include "utils/syscache.h"
 #include "utils/timestamp.h"
 
+#ifdef DEBUG_BRIN_STATS
+bool debug_brin_stats = false;
+#endif
+
 typedef struct MinmaxOpaque
 {
 	Oid			cached_subtype;
@@ -479,6 +483,13 @@ brin_minmax_count_overlaps(BrinRange **minranges, int nranges,
 {
 	int64	noverlaps;
 
+#ifdef DEBUG_BRIN_STATS
+	TimestampTz		start_ts;
+
+	if (debug_brin_stats)
+		start_ts = GetCurrentTimestamp();
+#endif
+
 	noverlaps = 0;
 	for (int i = 0; i < nranges; i++)
 	{
@@ -501,6 +512,16 @@ brin_minmax_count_overlaps(BrinRange **minranges, int nranges,
 	 */
 	noverlaps *= 2;
 
+#ifdef DEBUG_BRIN_STATS
+	if (debug_brin_stats)
+	{
+		elog(WARNING, "----- brin_minmax_count_overlaps -----");
+		elog(WARNING, "noverlaps = %ld", noverlaps);
+		elog(WARNING, "duration = %ld", TimestampDifferenceMilliseconds(start_ts,
+										GetCurrentTimestamp()));
+	}
+#endif
+
 	stats->avg_overlaps = (double) noverlaps / nranges;
 }
 
@@ -527,6 +548,13 @@ brin_minmax_match_tuples_to_ranges(BrinRanges *ranges,
 
 	int64  *unique = (int64 *) palloc0(sizeof(int64) * nvalues);
 
+#ifdef DEBUG_BRIN_STATS
+	TimestampTz		start_ts;
+
+	if (debug_brin_stats)
+		start_ts = GetCurrentTimestamp();
+#endif
+
 	/*
 	 * Build running count of unique values. We know there are unique[i]
 	 * unique values in values array up to index "i".
@@ -572,6 +600,18 @@ brin_minmax_match_tuples_to_ranges(BrinRanges *ranges,
 	Assert(nmatches >= 0);
 	Assert(nmatches_unique >= 0);
 
+#ifdef DEBUG_BRIN_STATS
+	if (debug_brin_stats)
+	{
+		elog(WARNING, "----- brin_minmax_match_tuples_to_ranges -----");
+		elog(WARNING, "nmatches = %ld %f", nmatches, (double) nmatches / numrows);
+		elog(WARNING, "nmatches unique = %ld %ld %f", nmatches_unique, nvalues_unique,
+			(double) nmatches_unique / nvalues_unique);
+		elog(WARNING, "duration = %ld", TimestampDifferenceMilliseconds(start_ts,
+									GetCurrentTimestamp()));
+	}
+#endif
+
 	stats->avg_matches = (double) nmatches / numrows;
 	stats->avg_matches_unique = (double) nmatches_unique / nvalues_unique;
 }
@@ -603,6 +643,13 @@ brin_minmax_value_stats(BrinRange **minranges, BrinRange **maxranges,
 			minval_corr = 0,
 			maxval_corr = 0;
 
+#ifdef DEBUG_BRIN_STATS
+	TimestampTz		start_ts;
+
+	if (debug_brin_stats)
+		start_ts = GetCurrentTimestamp();
+#endif
+
 	for (int i = 1; i < nranges; i++)
 	{
 		if (range_values_cmp(&minranges[i-1]->min_value, &minranges[i]->min_value, typcache) != 0)
@@ -625,6 +672,19 @@ brin_minmax_value_stats(BrinRange **minranges, BrinRange **maxranges,
 
 	stats->minval_correlation = (double) minval_corr / nranges;
 	stats->maxval_correlation = (double) maxval_corr / nranges;
+
+#ifdef DEBUG_BRIN_STATS
+	if (debug_brin_stats)
+	{
+		elog(WARNING, "----- brin_minmax_value_stats -----");
+		elog(WARNING, "minval ndistinct " INT64_FORMAT " correlation %f",
+			 stats->minval_ndistinct, stats->minval_correlation);
+		elog(WARNING, "maxval ndistinct " INT64_FORMAT " correlation %f",
+			 stats->maxval_ndistinct, stats->maxval_correlation);
+		elog(WARNING, "duration = %ld", TimestampDifferenceMilliseconds(start_ts,
+										GetCurrentTimestamp()));
+	}
+#endif
 }
 
 /*
@@ -649,6 +709,13 @@ brin_minmax_increment_stats(BrinRange **minranges, BrinRange **maxranges,
 			max_minval = 0,
 			max_maxval = 0;
 
+#ifdef DEBUG_BRIN_STATS
+	TimestampTz		start_ts;
+
+	if (debug_brin_stats)
+		start_ts = GetCurrentTimestamp();
+#endif
+
 	for (int i = 1; i < nranges; i++)
 	{
 		if (range_values_cmp(&minranges[i-1]->min_value, &minranges[i]->min_value, typcache) != 0)
@@ -700,6 +767,19 @@ brin_minmax_increment_stats(BrinRange **minranges, BrinRange **maxranges,
 		}
 	}
 
+#ifdef DEBUG_BRIN_STATS
+	if (debug_brin_stats)
+	{
+		elog(WARNING, "----- brin_minmax_increment_stats -----");
+		elog(WARNING, "minval ndistinct %ld sum %f max %f avg %f",
+			 minval_ndist, sum_minval, max_minval, sum_minval / minval_ndist);
+		elog(WARNING, "maxval ndistinct %ld sum %f max %f avg %f",
+			 maxval_ndist, sum_maxval, max_maxval, sum_maxval / maxval_ndist);
+		elog(WARNING, "duration = %ld", TimestampDifferenceMilliseconds(start_ts,
+										GetCurrentTimestamp()));
+	}
+#endif
+
 	stats->minval_increment_avg = (sum_minval / minval_ndist);
 	stats->minval_increment_max = max_minval;
 
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 67687d158e6..f8d06296fb1 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -96,6 +96,10 @@ extern bool ignore_checksum_failure;
 extern bool ignore_invalid_pages;
 extern bool synchronize_seqscans;
 
+#ifdef DEBUG_BRIN_STATS
+extern bool debug_brin_stats;
+#endif
+
 #ifdef TRACE_SYNCSCAN
 extern bool trace_syncscan;
 #endif
@@ -1230,6 +1234,20 @@ struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+#ifdef DEBUG_BRIN_STATS
+	/* this is undocumented because not exposed in a standard build */
+	{
+		{"debug_brin_stats", PGC_USERSET, DEVELOPER_OPTIONS,
+			gettext_noop("Print info about calculated BRIN statistics."),
+			NULL,
+			GUC_NOT_IN_SAMPLE
+		},
+		&debug_brin_stats,
+		false,
+		NULL, NULL, NULL
+	},
+#endif
+
 	{
 		{"exit_on_error", PGC_USERSET, ERROR_HANDLING_OPTIONS,
 			gettext_noop("Terminate session on any error."),
-- 
2.39.1