Show names of DEALLOCATE as constants in pg_stat_statements

This commit switches query jumbling so as prepared statement names are
treated as constants in DeallocateStmt.  A boolean field is added to
DeallocateStmt to make a distinction between ALL and named prepared
statements, as "name" was used to make this difference before, NULL
meaning DEALLOCATE ALL.

Prior to this commit, DEALLOCATE was not tracked in pg_stat_statements,
for the reason that it was not possible to treat its name parameter as a
constant.  Now that query jumbling applies to all the utility nodes,
this reason does not apply anymore.

Like 638d42a3c5, this can be a huge advantage for monitoring where
prepared statement names are randomly generated, preventing bloat in
pg_stat_statements.  A couple of tests are added to track the new
behavior.

Author: Dagfinn Ilmari Mannsåker, Michael Paquier
Reviewed-by: Julien Rouhaud
Discussion: https://postgr.es/m/ZMhT9kNtJJsHw6jK@paquier.xyz

contrib/pg_stat_statements/expected/utility.out

@@ -472,6 +472,47 @@ SELECT pg_stat_statements_reset();
  
 (1 row)
 
+-- Execution statements
+SELECT 1 as a;
+ a 
+---
+ 1
+(1 row)
+
+PREPARE stat_select AS SELECT $1 AS a;
+EXECUTE stat_select (1);
+ a 
+---
+ 1
+(1 row)
+
+DEALLOCATE stat_select;
+PREPARE stat_select AS SELECT $1 AS a;
+EXECUTE stat_select (2);
+ a 
+---
+ 2
+(1 row)
+
+DEALLOCATE PREPARE stat_select;
+DEALLOCATE ALL;
+DEALLOCATE PREPARE ALL;
+SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
+ calls | rows |                 query                 
+-------+------+---------------------------------------
+     2 |    0 | DEALLOCATE $1
+     2 |    0 | DEALLOCATE ALL
+     2 |    2 | PREPARE stat_select AS SELECT $1 AS a
+     1 |    1 | SELECT $1 as a
+     1 |    1 | SELECT pg_stat_statements_reset()
+(5 rows)
+
+SELECT pg_stat_statements_reset();
+ pg_stat_statements_reset 
+--------------------------
+ 
+(1 row)
+
 -- SET statements.
 -- These use two different strings, still they count as one entry.
 SET work_mem = '1MB';

contrib/pg_stat_statements/pg_stat_statements.c

@@ -104,8 +104,7 @@ static const uint32 PGSS_PG_MAJOR_VERSION = PG_VERSION_NUM / 100;
  * ignores.
  */
 #define PGSS_HANDLED_UTILITY(n)		(!IsA(n, ExecuteStmt) && \
-									!IsA(n, PrepareStmt) && \
-									!IsA(n, DeallocateStmt))
+									!IsA(n, PrepareStmt))
 
 /*
  * Extension version number, for supporting older extension versions' objects
@@ -830,8 +829,7 @@ pgss_post_parse_analyze(ParseState *pstate, Query *query, JumbleState *jstate)
 
 	/*
 	 * Clear queryId for prepared statements related utility, as those will
-	 * inherit from the underlying statement's one (except DEALLOCATE which is
-	 * entirely untracked).
+	 * inherit from the underlying statement's one.
 	 */
 	if (query->utilityStmt)
 	{
@@ -1116,8 +1114,6 @@ pgss_ProcessUtility(PlannedStmt *pstmt, const char *queryString,
 	 * calculated from the query tree) would be used to accumulate costs of
 	 * ensuing EXECUTEs.  This would be confusing, and inconsistent with other
 	 * cases where planning time is not included at all.
-	 *
-	 * Likewise, we don't track execution of DEALLOCATE.
 	 */
 	if (pgss_track_utility && pgss_enabled(exec_nested_level) &&
 		PGSS_HANDLED_UTILITY(parsetree))

contrib/pg_stat_statements/sql/utility.sql

@@ -237,6 +237,19 @@ DROP DOMAIN domain_stats;
 SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
 SELECT pg_stat_statements_reset();
 
+-- Execution statements
+SELECT 1 as a;
+PREPARE stat_select AS SELECT $1 AS a;
+EXECUTE stat_select (1);
+DEALLOCATE stat_select;
+PREPARE stat_select AS SELECT $1 AS a;
+EXECUTE stat_select (2);
+DEALLOCATE PREPARE stat_select;
+DEALLOCATE ALL;
+DEALLOCATE PREPARE ALL;
+SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
+SELECT pg_stat_statements_reset();
+
 -- SET statements.
 -- These use two different strings, still they count as one entry.
 SET work_mem = '1MB';

src/backend/parser/gram.y

@@ -11953,6 +11953,8 @@ DeallocateStmt: DEALLOCATE name
 						DeallocateStmt *n = makeNode(DeallocateStmt);
 
 						n->name = $2;
+						n->isall = false;
+						n->location = @2;
 						$$ = (Node *) n;
 					}
 				| DEALLOCATE PREPARE name
@@ -11960,6 +11962,8 @@ DeallocateStmt: DEALLOCATE name
 						DeallocateStmt *n = makeNode(DeallocateStmt);
 
 						n->name = $3;
+						n->isall = false;
+						n->location = @3;
 						$$ = (Node *) n;
 					}
 				| DEALLOCATE ALL
@@ -11967,6 +11971,8 @@ DeallocateStmt: DEALLOCATE name
 						DeallocateStmt *n = makeNode(DeallocateStmt);
 
 						n->name = NULL;
+						n->isall = true;
+						n->location = -1;
 						$$ = (Node *) n;
 					}
 				| DEALLOCATE PREPARE ALL
@@ -11974,6 +11980,8 @@ DeallocateStmt: DEALLOCATE name
 						DeallocateStmt *n = makeNode(DeallocateStmt);
 
 						n->name = NULL;
+						n->isall = true;
+						n->location = -1;
 						$$ = (Node *) n;
 					}
 		;

src/include/nodes/parsenodes.h

@@ -3929,8 +3929,12 @@ typedef struct ExecuteStmt
 typedef struct DeallocateStmt
 {
 	NodeTag		type;
-	char	   *name;			/* The name of the plan to remove */
-	/* NULL means DEALLOCATE ALL */
+	/* The name of the plan to remove, NULL if DEALLOCATE ALL */
+	char	   *name pg_node_attr(query_jumble_ignore);
+	/* true if DEALLOCATE ALL */
+	bool		isall;
+	/* token location, or -1 if unknown */
+	int			location pg_node_attr(query_jumble_location);
 } DeallocateStmt;
 
 /*