PG-1459 Keep username and datname empty if we cannont get real values

If we cannot get username and datname real values just keep these fields
empty.

Author: artemgavrilov

Makefile

@@ -29,6 +29,7 @@ REGRESS = basic \
 	squashing \
 	tags \
 	user \
+	rollback \
 	level_tracking \
 	decode_error_level \
 	parallel \

pg_stat_monitor.c

@@ -1743,19 +1743,16 @@ pgsm_create_hash_entry(uint64 bucket_id, int64 queryid, PlanInfo *plan_info)
 	{
 		datname = get_database_name(entry->key.dbid);
 		username = GetUserNameFromId(entry->key.userid, true);
-	}
-
-	if (!datname)
-		datname = pnstrdup("<database name not available>", sizeof(entry->datname) - 1);
 
-	if (!username)
-		username = pnstrdup("<user name not available>", sizeof(entry->username) - 1);
+		snprintf(entry->datname, sizeof(entry->datname), "%s", datname);
+		snprintf(entry->username, sizeof(entry->username), "%s", username);
 
-	snprintf(entry->datname, sizeof(entry->datname), "%s", datname);
-	snprintf(entry->username, sizeof(entry->username), "%s", username);
+		if (datname)
+			pfree(datname);
 
-	pfree(datname);
-	pfree(username);
+		if (username)
+			pfree(username);
+	}
 
 	MemoryContextSwitchTo(oldctx);
 

regression/expected/rollback.out

@@ -0,0 +1,72 @@
+CREATE EXTENSION pg_stat_monitor;
+CREATE USER u WITH SUPERUSER;
+SET ROLE u;
+CREATE TABLE t (a int PRIMARY KEY) ;
+SELECT pg_stat_monitor_reset();
+ pg_stat_monitor_reset 
+-----------------------
+ 
+(1 row)
+
+BEGIN;
+INSERT INTO t VALUES (1);
+COMMIT;
+SELECT query, username, datname FROM pg_stat_monitor ORDER BY query COLLATE "C";
+             query              | username |      datname       
+--------------------------------+----------+--------------------
+ BEGIN                          | u        | contrib_regression
+ COMMIT                         | u        | contrib_regression
+ INSERT INTO t VALUES (1)       | u        | contrib_regression
+ SELECT pg_stat_monitor_reset() | u        | contrib_regression
+(4 rows)
+
+SELECT pg_stat_monitor_reset();
+ pg_stat_monitor_reset 
+-----------------------
+ 
+(1 row)
+
+-- During manual rollback we will be able to get username and datname of the query that was rolled back.
+BEGIN;
+INSERT INTO t VALUES (2);
+ROLLBACK;
+SELECT query, username, datname FROM pg_stat_monitor ORDER BY query COLLATE "C";
+             query              | username |      datname       
+--------------------------------+----------+--------------------
+ BEGIN                          | u        | contrib_regression
+ INSERT INTO t VALUES (2)       | u        | contrib_regression
+ ROLLBACK                       | u        | contrib_regression
+ SELECT pg_stat_monitor_reset() | u        | contrib_regression
+(4 rows)
+
+SELECT pg_stat_monitor_reset();
+ pg_stat_monitor_reset 
+-----------------------
+ 
+(1 row)
+
+-- If transaction is rolled back due an error, we won't be able to get username and datname of the query that was rolled back.
+BEGIN;
+INSERT INTO t VALUES (1);
+ERROR:  duplicate key value violates unique constraint "t_pkey"
+DETAIL:  Key (a)=(1) already exists.
+ROLLBACK;
+SELECT query, username, datname FROM pg_stat_monitor ORDER BY query COLLATE "C";
+             query              | username |      datname       
+--------------------------------+----------+--------------------
+ BEGIN                          | u        | contrib_regression
+ INSERT INTO t VALUES (1);      | u        | contrib_regression
+ ROLLBACK                       |          | 
+ SELECT pg_stat_monitor_reset() | u        | contrib_regression
+(4 rows)
+
+SELECT pg_stat_monitor_reset();
+ pg_stat_monitor_reset 
+-----------------------
+ 
+(1 row)
+
+DROP TABLE t;
+SET ROLE NONE;
+DROP USER u;
+DROP EXTENSION pg_stat_monitor;

regression/sql/rollback.sql

@@ -0,0 +1,36 @@
+CREATE EXTENSION pg_stat_monitor;
+
+CREATE USER u WITH SUPERUSER;
+SET ROLE u;
+CREATE TABLE t (a int PRIMARY KEY) ;
+
+SELECT pg_stat_monitor_reset();
+
+BEGIN;
+INSERT INTO t VALUES (1);
+COMMIT;
+
+SELECT query, username, datname FROM pg_stat_monitor ORDER BY query COLLATE "C";
+SELECT pg_stat_monitor_reset();
+
+-- During manual rollback we will be able to get username and datname of the query that was rolled back.
+BEGIN;
+INSERT INTO t VALUES (2);
+ROLLBACK;
+
+SELECT query, username, datname FROM pg_stat_monitor ORDER BY query COLLATE "C";
+SELECT pg_stat_monitor_reset();
+
+-- If transaction is rolled back due an error, we won't be able to get username and datname of the query that was rolled back.
+BEGIN;
+INSERT INTO t VALUES (1);
+ROLLBACK;
+
+SELECT query, username, datname FROM pg_stat_monitor ORDER BY query COLLATE "C";
+SELECT pg_stat_monitor_reset();
+
+DROP TABLE t;
+SET ROLE NONE;
+DROP USER u;
+
+DROP EXTENSION pg_stat_monitor;