mariadb/mysql-test/main/consistent_snapshot.test
Sergei Golubchik bead24b7f3 mariadb-test: wait on disconnect
Remove one of the major sources of race condiitons in mariadb-test.
Normally, mariadb_close() sends COM_QUIT to the server and immediately
disconnects. In mariadb-test it means the test can switch to another
connection and sends queries to the server before the server even
started parsing the COM_QUIT packet and these queries can see the
connection as fully active, as it didn't reach dispatch_command yet.

This is a major source of instability in tests and many - but not all,
still less than a half - tests employ workarounds. The correct one
is a pair count_sessions.inc/wait_until_count_sessions.inc.
Also very popular was wait_until_disconnected.inc, which was completely
useless, because it verifies that the connection is closed, and after
disconnect it always is, it didn't verify whether the server processed
COM_QUIT. Sadly the placebo was as widely used as the real thing.

Let's fix this by making mariadb-test `disconnect` command _to wait_ for
the server to confirm. This makes almost all workarounds redundant.

In some cases count_sessions.inc/wait_until_count_sessions.inc is still
needed, though, as only `disconnect` command is changed:

 * after external tools, like `exec $MYSQL`
 * after failed `connect` command
 * replication, after `STOP SLAVE`
 * Federated/CONNECT/SPIDER/etc after `DROP TABLE`

and also in some XA tests, because an XA transaction is dissociated from
the THD very late, after the server has closed the client connection.

Collateral cleanups: fix comments, remove some redundant statements:
 * DROP IF EXISTS if nothing is known to exist
 * DROP table/view before DROP DATABASE
 * REVOKE privileges before DROP USER
 etc
2025-07-16 09:14:33 +07:00

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--source include/have_innodb.inc
connect (con1,localhost,root,,);
connect (con2,localhost,root,,);
--echo ### Test 1:
--echo ### - While a consistent snapshot transaction is executed,
--echo ### no external inserts should be visible to the transaction.
connection con1;
CREATE TABLE t1 (a INT) ENGINE=innodb;
START TRANSACTION WITH CONSISTENT SNAPSHOT;
connection con2;
INSERT INTO t1 VALUES(1);
connection con1;
SELECT * FROM t1; # if consistent snapshot was set as expected, we
# should see nothing.
COMMIT;
--echo ### Test 2:
--echo ### - For any non-consistent snapshot transaction, external
--echo ### committed inserts should be visible to the transaction.
DELETE FROM t1;
START TRANSACTION; # Now we omit WITH CONSISTENT SNAPSHOT
connection con2;
INSERT INTO t1 VALUES(1);
connection con1;
SELECT * FROM t1; # if consistent snapshot was not set, as expected, we
# should see 1.
COMMIT;
--echo ### Test 3:
--echo ### - Bug#44664: valgrind warning for COMMIT_AND_CHAIN and ROLLBACK_AND_CHAIN
--echo ### Chaining a transaction does not retain consistency level.
START TRANSACTION WITH CONSISTENT SNAPSHOT;
DELETE FROM t1;
COMMIT WORK AND CHAIN;
connection con2;
INSERT INTO t1 VALUES(1);
connection con1;
SELECT * FROM t1; # if consistent snapshot was not set, as expected, we
# should see 1.
COMMIT;
connection default;
disconnect con1;
disconnect con2;
DROP TABLE t1;
--echo # End of 4.1 tests