Track identical top vs nested queries independently in pg_stat_statements

Changing pg_stat_statements.track between 'all' and 'top' would control
if pg_stat_statements tracked just top level statements or also
statements inside functions, but when tracking all it would not
differentiate between the two. Being table to differentiate this is
useful both to track where the actual query is coming from, and to see
if there are differences in executions between the two.

To do this, add a boolean to the hash key indicating if the statement
was top level or not.

Experience from the pg_stat_kcache module shows that in at least some
"reasonable worloads" only <5% of the queries show up both top level and
nested. Based on this, admittedly small, dataset, this patch does not
try to de-duplicate those query *texts*, and will just store one copy
for the top level and one for the nested.

Author: Julien Rohaud
Reviewed-By: Magnus Hagander, Masahiro Ikeda
Discussion: https://postgr.es/m/20201202040516.GA43757@nol

contrib/pg_stat_statements/Makefile

@@ -6,7 +6,8 @@ OBJS = \
 	pg_stat_statements.o
 
 EXTENSION = pg_stat_statements
-DATA = pg_stat_statements--1.4.sql pg_stat_statements--1.8--1.9.sql \
+DATA = pg_stat_statements--1.4.sql \
+        pg_stat_statements--1.9--1.10.sql pg_stat_statements--1.8--1.9.sql \
 	pg_stat_statements--1.7--1.8.sql pg_stat_statements--1.6--1.7.sql \
 	pg_stat_statements--1.5--1.6.sql pg_stat_statements--1.4--1.5.sql \
 	pg_stat_statements--1.3--1.4.sql pg_stat_statements--1.2--1.3.sql \

contrib/pg_stat_statements/expected/pg_stat_statements.out

@@ -901,4 +901,44 @@ SELECT dealloc FROM pg_stat_statements_info;
        0
 (1 row)
 
+--
+-- top level handling
+--
+SET pg_stat_statements.track = 'top';
+DELETE FROM test;
+DO $$
+BEGIN
+    DELETE FROM test;
+END;
+$$ LANGUAGE plpgsql;
+SELECT query, toplevel, plans, calls FROM pg_stat_statements WHERE query LIKE '%DELETE%' ORDER BY query COLLATE "C", toplevel;
+         query         | toplevel | plans | calls 
+-----------------------+----------+-------+-------
+ DELETE FROM test      | t        |     1 |     1
+ DO $$                +| t        |     0 |     1
+ BEGIN                +|          |       | 
+     DELETE FROM test;+|          |       | 
+ END;                 +|          |       | 
+ $$ LANGUAGE plpgsql   |          |       | 
+(2 rows)
+
+SET pg_stat_statements.track = 'all';
+DELETE FROM test;
+DO $$
+BEGIN
+    DELETE FROM test;
+END;
+$$ LANGUAGE plpgsql;
+SELECT query, toplevel, plans, calls FROM pg_stat_statements WHERE query LIKE '%DELETE%' ORDER BY query COLLATE "C", toplevel;
+         query         | toplevel | plans | calls 
+-----------------------+----------+-------+-------
+ DELETE FROM test      | f        |     1 |     1
+ DELETE FROM test      | t        |     2 |     2
+ DO $$                +| t        |     0 |     2
+ BEGIN                +|          |       | 
+     DELETE FROM test;+|          |       | 
+ END;                 +|          |       | 
+ $$ LANGUAGE plpgsql   |          |       | 
+(3 rows)
+
 DROP EXTENSION pg_stat_statements;

contrib/pg_stat_statements/pg_stat_statements--1.9--1.10.sql

@@ -0,0 +1,57 @@
+/* contrib/pg_stat_statements/pg_stat_statements--1.9--1.10.sql */
+
+-- complain if script is sourced in psql, rather than via ALTER EXTENSION
+\echo Use "ALTER EXTENSION pg_stat_statements UPDATE TO '1.10'" to load this file. \quit
+
+/* First we have to remove them from the extension */
+ALTER EXTENSION pg_stat_statements DROP VIEW pg_stat_statements;
+ALTER EXTENSION pg_stat_statements DROP FUNCTION pg_stat_statements(boolean);
+
+/* Then we can drop them */
+DROP VIEW pg_stat_statements;
+DROP FUNCTION pg_stat_statements(boolean);
+
+/* Now redefine */
+CREATE FUNCTION pg_stat_statements(IN showtext boolean,
+    OUT userid oid,
+    OUT dbid oid,
+    OUT toplevel bool,
+    OUT queryid bigint,
+    OUT query text,
+    OUT plans int8,
+    OUT total_plan_time float8,
+    OUT min_plan_time float8,
+    OUT max_plan_time float8,
+    OUT mean_plan_time float8,
+    OUT stddev_plan_time float8,
+    OUT calls int8,
+    OUT total_exec_time float8,
+    OUT min_exec_time float8,
+    OUT max_exec_time float8,
+    OUT mean_exec_time float8,
+    OUT stddev_exec_time float8,
+    OUT rows int8,
+    OUT shared_blks_hit int8,
+    OUT shared_blks_read int8,
+    OUT shared_blks_dirtied int8,
+    OUT shared_blks_written int8,
+    OUT local_blks_hit int8,
+    OUT local_blks_read int8,
+    OUT local_blks_dirtied int8,
+    OUT local_blks_written int8,
+    OUT temp_blks_read int8,
+    OUT temp_blks_written int8,
+    OUT blk_read_time float8,
+    OUT blk_write_time float8,
+    OUT wal_records int8,
+    OUT wal_fpi int8,
+    OUT wal_bytes numeric
+)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'pg_stat_statements_1_10'
+LANGUAGE C STRICT VOLATILE PARALLEL SAFE;
+
+CREATE VIEW pg_stat_statements AS
+  SELECT * FROM pg_stat_statements(true);
+
+GRANT SELECT ON pg_stat_statements TO PUBLIC;

contrib/pg_stat_statements/pg_stat_statements.c

@@ -87,7 +87,7 @@ PG_MODULE_MAGIC;
 #define PGSS_TEXT_FILE	PG_STAT_TMP_DIR "/pgss_query_texts.stat"
 
 /* Magic number identifying the stats file format */
-static const uint32 PGSS_FILE_HEADER = 0x20201218;
+static const uint32 PGSS_FILE_HEADER = 0x20201227;
 
 /* PostgreSQL major version number, changes in which invalidate all entries */
 static const uint32 PGSS_PG_MAJOR_VERSION = PG_VERSION_NUM / 100;
@@ -119,7 +119,8 @@ typedef enum pgssVersion
 	PGSS_V1_1,
 	PGSS_V1_2,
 	PGSS_V1_3,
-	PGSS_V1_8
+	PGSS_V1_8,
+	PGSS_V1_10
 } pgssVersion;
 
 typedef enum pgssStoreKind
@@ -141,16 +142,17 @@ typedef enum pgssStoreKind
  * Hashtable key that defines the identity of a hashtable entry.  We separate
  * queries by user and by database even if they are otherwise identical.
  *
- * Right now, this structure contains no padding.  If you add any, make sure
- * to teach pgss_store() to zero the padding bytes.  Otherwise, things will
- * break, because pgss_hash is created using HASH_BLOBS, and thus tag_hash
- * is used to hash this.
+ * If you add a new key to this struct, make sure to teach pgss_store() to
+ * zero the padding bytes.  Otherwise, things will break, because pgss_hash is
+ * created using HASH_BLOBS, and thus tag_hash is used to hash this.
+
  */
 typedef struct pgssHashKey
 {
 	Oid			userid;			/* user OID */
 	Oid			dbid;			/* database OID */
 	uint64		queryid;		/* query identifier */
+	bool		toplevel;		/* query executed at top level */
 } pgssHashKey;
 
 /*
@@ -297,6 +299,7 @@ PG_FUNCTION_INFO_V1(pg_stat_statements_reset_1_7);
 PG_FUNCTION_INFO_V1(pg_stat_statements_1_2);
 PG_FUNCTION_INFO_V1(pg_stat_statements_1_3);
 PG_FUNCTION_INFO_V1(pg_stat_statements_1_8);
+PG_FUNCTION_INFO_V1(pg_stat_statements_1_10);
 PG_FUNCTION_INFO_V1(pg_stat_statements);
 PG_FUNCTION_INFO_V1(pg_stat_statements_info);
 
@@ -1224,9 +1227,14 @@ pgss_store(const char *query, uint64 queryId,
 	query = CleanQuerytext(query, &query_location, &query_len);
 
 	/* Set up key for hashtable search */
+
+	/* memset() is required when pgssHashKey is without padding only */
+	memset(&key, 0, sizeof(pgssHashKey));
+
 	key.userid = GetUserId();
 	key.dbid = MyDatabaseId;
 	key.queryid = queryId;
+	key.toplevel = (exec_nested_level == 0);
 
 	/* Lookup the hash table entry with shared lock. */
 	LWLockAcquire(pgss->lock, LW_SHARED);
@@ -1406,7 +1414,8 @@ pg_stat_statements_reset(PG_FUNCTION_ARGS)
 #define PG_STAT_STATEMENTS_COLS_V1_2	19
 #define PG_STAT_STATEMENTS_COLS_V1_3	23
 #define PG_STAT_STATEMENTS_COLS_V1_8	32
-#define PG_STAT_STATEMENTS_COLS			32	/* maximum of above */
+#define PG_STAT_STATEMENTS_COLS_V1_10	33
+#define PG_STAT_STATEMENTS_COLS			33	/* maximum of above */
 
 /*
  * Retrieve statement statistics.
@@ -1418,6 +1427,16 @@ pg_stat_statements_reset(PG_FUNCTION_ARGS)
  * expected API version is identified by embedding it in the C name of the
  * function.  Unfortunately we weren't bright enough to do that for 1.1.
  */
+Datum
+pg_stat_statements_1_10(PG_FUNCTION_ARGS)
+{
+	bool		showtext = PG_GETARG_BOOL(0);
+
+	pg_stat_statements_internal(fcinfo, PGSS_V1_10, showtext);
+
+	return (Datum) 0;
+}
+
 Datum
 pg_stat_statements_1_8(PG_FUNCTION_ARGS)
 {
@@ -1537,6 +1556,10 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
 			if (api_version != PGSS_V1_8)
 				elog(ERROR, "incorrect number of output arguments");
 			break;
+		case PG_STAT_STATEMENTS_COLS_V1_10:
+			if (api_version != PGSS_V1_10)
+				elog(ERROR, "incorrect number of output arguments");
+			break;
 		default:
 			elog(ERROR, "incorrect number of output arguments");
 	}
@@ -1628,6 +1651,8 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
 
 		values[i++] = ObjectIdGetDatum(entry->key.userid);
 		values[i++] = ObjectIdGetDatum(entry->key.dbid);
+		if (api_version >= PGSS_V1_10)
+			values[i++] = BoolGetDatum(entry->key.toplevel);
 
 		if (is_allowed_role || entry->key.userid == userid)
 		{
@@ -1765,6 +1790,7 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
 					 api_version == PGSS_V1_2 ? PG_STAT_STATEMENTS_COLS_V1_2 :
 					 api_version == PGSS_V1_3 ? PG_STAT_STATEMENTS_COLS_V1_3 :
 					 api_version == PGSS_V1_8 ? PG_STAT_STATEMENTS_COLS_V1_8 :
+					 api_version == PGSS_V1_10 ? PG_STAT_STATEMENTS_COLS_V1_10 :
 					 -1 /* fail if you forget to update this assert */ ));
 
 		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
@@ -2437,10 +2463,20 @@ entry_reset(Oid userid, Oid dbid, uint64 queryid)
 	if (userid != 0 && dbid != 0 && queryid != UINT64CONST(0))
 	{
 		/* If all the parameters are available, use the fast path. */
+		memset(&key, 0, sizeof(pgssHashKey));
 		key.userid = userid;
 		key.dbid = dbid;
 		key.queryid = queryid;
 
+		/* Remove the key if it exists, starting with the top-level entry  */
+		key.toplevel = false;
+		entry = (pgssEntry *) hash_search(pgss_hash, &key, HASH_REMOVE, NULL);
+		if (entry)				/* found */
+			num_remove++;
+
+		/* Also remove entries for top level statements */
+		key.toplevel = true;
+
 		/* Remove the key if exists */
 		entry = (pgssEntry *) hash_search(pgss_hash, &key, HASH_REMOVE, NULL);
 		if (entry)				/* found */

contrib/pg_stat_statements/pg_stat_statements.control

@@ -1,5 +1,5 @@
 # pg_stat_statements extension
 comment = 'track planning and execution statistics of all SQL statements executed'
-default_version = '1.9'
+default_version = '1.10'
 module_pathname = '$libdir/pg_stat_statements'
 relocatable = true

contrib/pg_stat_statements/sql/pg_stat_statements.sql

@@ -364,4 +364,25 @@ SELECT query, plans, calls, rows FROM pg_stat_statements ORDER BY query COLLATE
 SELECT pg_stat_statements_reset();
 SELECT dealloc FROM pg_stat_statements_info;
 
+--
+-- top level handling
+--
+SET pg_stat_statements.track = 'top';
+DELETE FROM test;
+DO $$
+BEGIN
+    DELETE FROM test;
+END;
+$$ LANGUAGE plpgsql;
+SELECT query, toplevel, plans, calls FROM pg_stat_statements WHERE query LIKE '%DELETE%' ORDER BY query COLLATE "C", toplevel;
+
+SET pg_stat_statements.track = 'all';
+DELETE FROM test;
+DO $$
+BEGIN
+    DELETE FROM test;
+END;
+$$ LANGUAGE plpgsql;
+SELECT query, toplevel, plans, calls FROM pg_stat_statements WHERE query LIKE '%DELETE%' ORDER BY query COLLATE "C", toplevel;
+
 DROP EXTENSION pg_stat_statements;

doc/src/sgml/pgstatstatements.sgml

@@ -87,6 +87,15 @@
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>toplevel</structfield> <type>bool</type>
+      </para>
+      <para>
+       True if the query was executed as a top level statement
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>queryid</structfield> <type>bigint</type>