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 638d42a3c520, 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

1 files changed, 13 insertions, 0 deletions

diff --git a/contrib/pg_stat_statements/sql/utility.sql b/contrib/pg_stat_statements/sql/utility.sql
index 87666d9135f..5f7d4a467f0 100644
--- a/contrib/pg_stat_statements/sql/utility.sql
+++ b/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';