Allow pg_stat_statements to track WAL usage statistics.

Amit Kapila · Amit Kapila · commit 6b466bf5f2be · 2020-04-05T07:34:04.000+05:30
This commit adds three new columns in pg_stat_statements output to display WAL usage statistics added by commit df3b181. This commit doesn't bump the version of pg_stat_statements as the same is done for this release in commit 17e0328. Author: Kirill Bychik and Julien Rouhaud Reviewed-by: Julien Rouhaud, Fujii Masao, Dilip Kumar and Amit Kapila Discussion: https://postgr.es/m/CAB-hujrP8ZfUkvL5OYETipQwA=e3n7oqHFU=4ZLxWS_Cza3kQQ@mail.gmail.com
diff --git a/contrib/pg_stat_statements/expected/pg_stat_statements.out b/contrib/pg_stat_statements/expected/pg_stat_statements.out
@@ -211,6 +211,45 @@ SELECT query, calls, rows FROM pg_stat_statements ORDER BY query COLLATE "C";
  UPDATE test SET b = $1 WHERE a > $2                                          |     1 |    3
 (10 rows)
 
+--
+-- INSERT, UPDATE, DELETE on test table to validate WAL generation metrics
+--
+SELECT pg_stat_statements_reset();
+ pg_stat_statements_reset 
+--------------------------
+ 
+(1 row)
+
+-- utility "create table" should not be shown
+CREATE TABLE pgss_test (a int, b char(20));
+INSERT INTO pgss_test VALUES(generate_series(1, 10), 'aaa');
+UPDATE pgss_test SET b = 'bbb' WHERE a > 7;
+DELETE FROM pgss_test WHERE a > 9;
+-- DROP test table
+SET pg_stat_statements.track_utility = TRUE;
+DROP TABLE pgss_test;
+SET pg_stat_statements.track_utility = FALSE;
+-- Check WAL is generated for the above statements
+SELECT query, calls, rows,
+wal_bytes > 0 as wal_bytes_generated,
+wal_records > 0 as wal_records_generated,
+wal_records = rows as wal_records_as_rows
+FROM pg_stat_statements ORDER BY query COLLATE "C";
+                           query                           | calls | rows | wal_bytes_generated | wal_records_generated | wal_records_as_rows 
+-----------------------------------------------------------+-------+------+---------------------+-----------------------+---------------------
+ DELETE FROM pgss_test WHERE a > $1                        |     1 |    1 | t                   | t                     | t
+ DROP TABLE pgss_test                                      |     1 |    0 | t                   | t                     | f
+ INSERT INTO pgss_test VALUES(generate_series($1, $2), $3) |     1 |   10 | t                   | t                     | t
+ SELECT pg_stat_statements_reset()                         |     1 |    1 | f                   | f                     | f
+ SELECT query, calls, rows,                               +|     0 |    0 | f                   | f                     | t
+ wal_bytes > $1 as wal_bytes_generated,                   +|       |      |                     |                       | 
+ wal_records > $2 as wal_records_generated,               +|       |      |                     |                       | 
+ wal_records = rows as wal_records_as_rows                +|       |      |                     |                       | 
+ FROM pg_stat_statements ORDER BY query COLLATE "C"        |       |      |                     |                       | 
+ SET pg_stat_statements.track_utility = FALSE              |     1 |    0 | f                   | f                     | t
+ UPDATE pgss_test SET b = $1 WHERE a > $2                  |     1 |    3 | t                   | t                     | t
+(7 rows)
+
 --
 -- pg_stat_statements.track = none
 --
diff --git a/contrib/pg_stat_statements/pg_stat_statements--1.7--1.8.sql b/contrib/pg_stat_statements/pg_stat_statements--1.7--1.8.sql
@@ -41,7 +41,10 @@ CREATE FUNCTION pg_stat_statements(IN showtext boolean,
     OUT temp_blks_read int8,
     OUT temp_blks_written int8,
     OUT blk_read_time float8,
-    OUT blk_write_time float8
+    OUT blk_write_time float8,
+    OUT wal_records int8,
+    OUT wal_num_fpw int8,
+    OUT wal_bytes numeric
 )
 RETURNS SETOF record
 AS 'MODULE_PATHNAME', 'pg_stat_statements_1_8'
diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -188,6 +188,9 @@ typedef struct Counters
 	double		blk_read_time;	/* time spent reading, in msec */
 	double		blk_write_time; /* time spent writing, in msec */
 	double		usage;			/* usage factor */
+	int64		wal_records;	/* # of WAL records generated */
+	int64		wal_num_fpw;	/* # of WAL full page image records generated */
+	uint64		wal_bytes;		/* total amount of WAL bytes generated */
 } Counters;
 
 /*
@@ -348,6 +351,7 @@ static void pgss_store(const char *query, uint64 queryId,
 					   pgssStoreKind kind,
 					   double total_time, uint64 rows,
 					   const BufferUsage *bufusage,
+					   const WalUsage *walusage,
 					   pgssJumbleState *jstate);
 static void pg_stat_statements_internal(FunctionCallInfo fcinfo,
 										pgssVersion api_version,
@@ -891,6 +895,7 @@ pgss_post_parse_analyze(ParseState *pstate, Query *query)
 				   0,
 				   0,
 				   NULL,
+				   NULL,
 				   &jstate);
 }
 
@@ -926,9 +931,17 @@ pgss_planner(Query *parse,
 		instr_time	duration;
 		BufferUsage bufusage_start,
 					bufusage;
+		WalUsage	walusage_start,
+					walusage;
 
 		/* We need to track buffer usage as the planner can access them. */
 		bufusage_start = pgBufferUsage;
+
+		/*
+		 * Similarly the planner could write some WAL records in some cases
+		 * (e.g. setting a hint bit with those being WAL-logged)
+		 */
+		walusage_start = pgWalUsage;
 		INSTR_TIME_SET_CURRENT(start);
 
 		plan_nested_level++;
@@ -954,6 +967,10 @@ pgss_planner(Query *parse,
 		memset(&bufusage, 0, sizeof(BufferUsage));
 		BufferUsageAccumDiff(&bufusage, &pgBufferUsage, &bufusage_start);
 
+		/* calc differences of WAL counters. */
+		memset(&walusage, 0, sizeof(WalUsage));
+		WalUsageAccumDiff(&walusage, &pgWalUsage, &walusage_start);
+
 		pgss_store(query_string,
 				   parse->queryId,
 				   parse->stmt_location,
@@ -962,6 +979,7 @@ pgss_planner(Query *parse,
 				   INSTR_TIME_GET_MILLISEC(duration),
 				   0,
 				   &bufusage,
+				   &walusage,
 				   NULL);
 	}
 	else
@@ -1079,6 +1097,7 @@ pgss_ExecutorEnd(QueryDesc *queryDesc)
 				   queryDesc->totaltime->total * 1000.0,	/* convert to msec */
 				   queryDesc->estate->es_processed,
 				   &queryDesc->totaltime->bufusage,
+				   &queryDesc->totaltime->walusage,
 				   NULL);
 	}
 
@@ -1123,8 +1142,11 @@ pgss_ProcessUtility(PlannedStmt *pstmt, const char *queryString,
 		uint64		rows;
 		BufferUsage bufusage_start,
 					bufusage;
+		WalUsage	walusage_start,
+					walusage;
 
 		bufusage_start = pgBufferUsage;
+		walusage_start = pgWalUsage;
 		INSTR_TIME_SET_CURRENT(start);
 
 		exec_nested_level++;
@@ -1154,6 +1176,10 @@ pgss_ProcessUtility(PlannedStmt *pstmt, const char *queryString,
 		memset(&bufusage, 0, sizeof(BufferUsage));
 		BufferUsageAccumDiff(&bufusage, &pgBufferUsage, &bufusage_start);
 
+		/* calc differences of WAL counters. */
+		memset(&walusage, 0, sizeof(WalUsage));
+		WalUsageAccumDiff(&walusage, &pgWalUsage, &walusage_start);
+
 		pgss_store(queryString,
 				   0,			/* signal that it's a utility stmt */
 				   pstmt->stmt_location,
@@ -1162,6 +1188,7 @@ pgss_ProcessUtility(PlannedStmt *pstmt, const char *queryString,
 				   INSTR_TIME_GET_MILLISEC(duration),
 				   rows,
 				   &bufusage,
+				   &walusage,
 				   NULL);
 	}
 	else
@@ -1197,7 +1224,8 @@ pgss_hash_string(const char *str, int len)
  *
  * If jstate is not NULL then we're trying to create an entry for which
  * we have no statistics as yet; we just want to record the normalized
- * query string.  total_time, rows, bufusage are ignored in this case.
+ * query string.  total_time, rows, bufusage and walusage are ignored in this
+ * case.
  *
  * If kind is PGSS_PLAN or PGSS_EXEC, its value is used as the array position
  * for the arrays in the Counters field.
@@ -1208,6 +1236,7 @@ pgss_store(const char *query, uint64 queryId,
 		   pgssStoreKind kind,
 		   double total_time, uint64 rows,
 		   const BufferUsage *bufusage,
+		   const WalUsage *walusage,
 		   pgssJumbleState *jstate)
 {
 	pgssHashKey key;
@@ -1402,6 +1431,9 @@ pgss_store(const char *query, uint64 queryId,
 		e->counters.blk_read_time += INSTR_TIME_GET_MILLISEC(bufusage->blk_read_time);
 		e->counters.blk_write_time += INSTR_TIME_GET_MILLISEC(bufusage->blk_write_time);
 		e->counters.usage += USAGE_EXEC(total_time);
+		e->counters.wal_records += walusage->wal_records;
+		e->counters.wal_num_fpw += walusage->wal_num_fpw;
+		e->counters.wal_bytes += walusage->wal_bytes;
 
 		SpinLockRelease(&e->mutex);
 	}
@@ -1449,8 +1481,8 @@ pg_stat_statements_reset(PG_FUNCTION_ARGS)
 #define PG_STAT_STATEMENTS_COLS_V1_1	18
 #define PG_STAT_STATEMENTS_COLS_V1_2	19
 #define PG_STAT_STATEMENTS_COLS_V1_3	23
-#define PG_STAT_STATEMENTS_COLS_V1_8	29
-#define PG_STAT_STATEMENTS_COLS			29	/* maximum of above */
+#define PG_STAT_STATEMENTS_COLS_V1_8	32
+#define PG_STAT_STATEMENTS_COLS			32	/* maximum of above */
 
 /*
  * Retrieve statement statistics.
@@ -1786,6 +1818,23 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
 			values[i++] = Float8GetDatumFast(tmp.blk_read_time);
 			values[i++] = Float8GetDatumFast(tmp.blk_write_time);
 		}
+		if (api_version >= PGSS_V1_8)
+		{
+			char		buf[256];
+			Datum		wal_bytes;
+
+			values[i++] = Int64GetDatumFast(tmp.wal_records);
+			values[i++] = Int64GetDatumFast(tmp.wal_num_fpw);
+
+			snprintf(buf, sizeof buf, UINT64_FORMAT, tmp.wal_bytes);
+
+			/* Convert to numeric. */
+			wal_bytes = DirectFunctionCall3(numeric_in,
+											CStringGetDatum(buf),
+											ObjectIdGetDatum(0),
+											Int32GetDatum(-1));
+			values[i++] = wal_bytes;
+		}
 
 		Assert(i == (api_version == PGSS_V1_0 ? PG_STAT_STATEMENTS_COLS_V1_0 :
 					 api_version == PGSS_V1_1 ? PG_STAT_STATEMENTS_COLS_V1_1 :
diff --git a/contrib/pg_stat_statements/sql/pg_stat_statements.sql b/contrib/pg_stat_statements/sql/pg_stat_statements.sql
@@ -101,6 +101,29 @@ SELECT * FROM test WHERE a IN (1, 2, 3, 4, 5);
 
 SELECT query, calls, rows FROM pg_stat_statements ORDER BY query COLLATE "C";
 
+--
+-- INSERT, UPDATE, DELETE on test table to validate WAL generation metrics
+--
+SELECT pg_stat_statements_reset();
+
+-- utility "create table" should not be shown
+CREATE TABLE pgss_test (a int, b char(20));
+
+INSERT INTO pgss_test VALUES(generate_series(1, 10), 'aaa');
+UPDATE pgss_test SET b = 'bbb' WHERE a > 7;
+DELETE FROM pgss_test WHERE a > 9;
+-- DROP test table
+SET pg_stat_statements.track_utility = TRUE;
+DROP TABLE pgss_test;
+SET pg_stat_statements.track_utility = FALSE;
+
+-- Check WAL is generated for the above statements
+SELECT query, calls, rows,
+wal_bytes > 0 as wal_bytes_generated,
+wal_records > 0 as wal_records_generated,
+wal_records = rows as wal_records_as_rows
+FROM pg_stat_statements ORDER BY query COLLATE "C";
+
 --
 -- pg_stat_statements.track = none
 --
diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml
@@ -264,6 +264,33 @@
       </entry>
      </row>
 
+     <row>
+      <entry><structfield>wal_bytes</structfield></entry>
+      <entry><type>numeric</type></entry>
+      <entry></entry>
+      <entry>
+        Total amount of WAL bytes generated by the statement
+      </entry>
+     </row>
+
+     <row>
+      <entry><structfield>wal_records</structfield></entry>
+      <entry><type>bigint</type></entry>
+      <entry></entry>
+      <entry>
+        Total count of WAL records generated by the statement
+      </entry>
+     </row>
+
+     <row>
+      <entry><structfield>wal_num_fpw</structfield></entry>
+      <entry><type>bigint</type></entry>
+      <entry></entry>
+      <entry>
+        Total count of WAL full page writes generated by the statement
+      </entry>
+     </row>
+
     </tbody>
    </tgroup>
   </table>
