From cba6bbfbd4dd4f7e6312dfc82c7ae847adc57aff Mon Sep 17 00:00:00 2001
From: Ibrar Ahmed <ibrar.ahmad@gmail.com>
Date: Thu, 11 Feb 2021 19:07:39 +0000
Subject: [PATCH] PG-177: Error in Histogram ranges.

---
 docs/USER_GUIDE.md | 26 +++++++++++++-------------
 pg_stat_monitor.c  | 45 ++++++++++++---------------------------------
 pg_stat_monitor.h  |  1 -
 3 files changed, 25 insertions(+), 47 deletions(-)

diff --git a/docs/USER_GUIDE.md b/docs/USER_GUIDE.md
index 855ca5b..9490e2e 100644
--- a/docs/USER_GUIDE.md
+++ b/docs/USER_GUIDE.md
@@ -284,19 +284,19 @@ SELECT resp_calls, query FROM pg_stat_monitor;
 {3," 0"," 0"," 0"," 0"," 0"," 0"," 0"," 0"," 1"} | select * from pg_stat_monitor_reset()
 {3," 0"," 0"," 0"," 0"," 0"," 0"," 0"," 0"," 1"} | SELECT * FROM foo
 
-SELECT * FROM histogram(4, '4B64EE85C83D9AAC') AS a(range TEXT, freq INT, bar TEXT);
-   range   | freq |              bar
------------+------+--------------------------------
- (0 - 1)}  |  692 | ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■
- (1 - 1)}  |    0 |
- (1 - 1)}  |    0 |
- (1 - 2)}  |  572 | ■■■■■■■■■■■■■■■■■■■■■■■■■
- (2 - 3)}  |   74 | ■■■
- (3 - 3)}  |    0 |
- (3 - 5)}  |    9 |
- (5 - 6)}  |    1 |
- (6 - 7)}  |    1 |
- (7 - 10)} |    1 |
+postgres=# SELECT * FROM histogram(0, 'F44CD1B4B33A47AF') AS a(range TEXT, freq INT, bar TEXT);
+       range        | freq |              bar
+--------------------+------+--------------------------------
+  (0 - 3)}          |    2 | ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■
+  (3 - 10)}         |    0 |
+  (10 - 31)}        |    1 | ■■■■■■■■■■■■■■■
+  (31 - 100)}       |    0 |
+  (100 - 316)}      |    0 |
+  (316 - 1000)}     |    0 |
+  (1000 - 3162)}    |    0 |
+  (3162 - 10000)}   |    0 |
+  (10000 - 31622)}  |    0 |
+  (31622 - 100000)} |    0 |
 (10 rows)
 ```
 
diff --git a/pg_stat_monitor.c b/pg_stat_monitor.c
index e0b3653..fccfbf6 100644
--- a/pg_stat_monitor.c
+++ b/pg_stat_monitor.c
@@ -103,7 +103,6 @@ PG_FUNCTION_INFO_V1(get_histogram_timings);
 static uint pg_get_client_addr(void);
 static int pg_get_application_name(char* application_name);
 static PgBackendStatus *pg_get_backend_status(void);
-static Datum textarray_get_datum(char **arr, int arr_len, int str_len);
 static Datum intarray_get_datum(int32 arr[], int len);
 
 #if PG_VERSION_NUM >= 130000
@@ -2263,35 +2262,6 @@ comp_location(const void *a, const void *b)
 }
 
 #define MAX_STRING_LEN	1024
-/* Convert array into Text dataum */
-static Datum
-textarray_get_datum(char **arr, int arr_len, int str_len)
-{
-	int     j;
-	char    *text_str = palloc0(MAX_STRING_LEN);
-	bool    first = true;
-
-	/* Sanity check */
-	if (arr == NULL || str_len >= MAX_STRING_LEN)
-		return 0;
-
-	/* Need to calculate the actual size, and avoid unnessary memory usage */
-	for (j = 0; j < arr_len; j++)
-	{
-		if (arr[j] == NULL || strlen(arr[j]) == 0)
-			continue;
-		if (first)
-		{
-			snprintf(text_str, MAX_STRING_LEN, "%s", arr[j]);
-			first = false;
-			continue;
-		}
-		snprintf(text_str, MAX_STRING_LEN, "%s,%s", text_str, arr[j]);
-	}
-	return CStringGetTextDatum(text_str);
-
-}
-
 /* Convert array into Text dataum */
 static Datum
 intarray_get_datum(int32 arr[], int len)
@@ -2759,7 +2729,8 @@ get_histogram_timings(PG_FUNCTION_ARGS)
 	double b_max;
 	double b_min;
 	double bucket_size;
-	char   range[50][1024] = {0};
+	bool	first = true;
+	char    *text_str = palloc0(MAX_STRING_LEN);
 
 	b_max = log(q_max - q_min);
 	b_min = 0;
@@ -2768,8 +2739,16 @@ get_histogram_timings(PG_FUNCTION_ARGS)
 	{
 		int64 b_start = (index == 1)? 0 : exp(bucket_size * (index - 1));
 		int64 b_end = exp(bucket_size * index);
-		sprintf(range[index-1], "(%ld - %ld)}", b_start, b_end);
+		if (first)
+		{
+			sprintf(text_str, "(%ld - %ld)}", b_start, b_end);
+			first = false;
+		}
+		else
+		{
+			sprintf(text_str, "%s, (%ld - %ld)}", text_str, b_start, b_end);
+		}
 	}
-	return TextArrayGetTextDatum((char**)range, b_count, 1023);
+	return CStringGetTextDatum(text_str);
 }
 
diff --git a/pg_stat_monitor.h b/pg_stat_monitor.h
index 407b8a1..4a62e32 100644
--- a/pg_stat_monitor.h
+++ b/pg_stat_monitor.h
@@ -54,7 +54,6 @@
 #include "utils/guc.h"
 
 #define MAX_BACKEND_PROCESES (MaxBackends + NUM_AUXILIARY_PROCS + max_prepared_xacts)
-#define  TextArrayGetTextDatum(x,y,z) textarray_get_datum(x,y,z)
 #define  IntArrayGetTextDatum(x,y) intarray_get_datum(x,y)
 
 /* XXX: Should USAGE_EXEC reflect execution time and/or buffer usage? */