MDEV-40661: mysql_upgrade.test not stable on a busy server

[gkodinov]

The cleanup of the old connection goes on in the background. It can take longer on a busy server and this trigger the active sessions warning in DROP user.
Stabilized the test by counting the number of session prior to upgrade and waiting for the count after.

[gkodinov]

Note a similar PR: #5344

[Copilot]

Pull request overview

Stabilizes mysql-test/main/mysql_upgrade.test for busy servers by ensuring mysql_upgrade’s background connection cleanup has completed (as measured by returning to the pre-upgrade session count) before running DROP USER, avoiding intermittent “active sessions” warnings.

Changes:

• Capture the current Threads_connected count before selected mysql_upgrade invocations.
• Wait after mysql_upgrade until Threads_connected returns to (or below) the pre-upgrade baseline before dropping affected users.
• Apply this pattern across several upgrade scenarios within the same test.

Suppressed comments (5)

mysql-test/main/mysql_upgrade.test:209

• This --source line has trailing whitespace after the include filename. While mysqltest currently tolerates it, it adds noise and can be error-prone in tooling; please remove the trailing space.

--source include/wait_until_count_sessions.inc 

mysql-test/main/mysql_upgrade.test:140

• This --source line has trailing whitespace after the include filename. While mysqltest currently tolerates it, it adds noise and can be error-prone in tooling; please remove the trailing space.

--source include/wait_until_count_sessions.inc 

mysql-test/main/mysql_upgrade.test:425

• This --source line has trailing whitespace after the include filename. While mysqltest currently tolerates it, it adds noise and can be error-prone in tooling; please remove the trailing space.

--source include/wait_until_count_sessions.inc 

mysql-test/main/mysql_upgrade.test:458

• This --source line has trailing whitespace after the include filename. While mysqltest currently tolerates it, it adds noise and can be error-prone in tooling; please remove the trailing space.

--source include/wait_until_count_sessions.inc 

mysql-test/main/mysql_upgrade.test:605

• This --source line has trailing whitespace after the include filename. While mysqltest currently tolerates it, it adds noise and can be error-prone in tooling; please remove the trailing space.

--source include/wait_until_count_sessions.inc 

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[svoj]

@vuvova seem to prefer to disable_warnings: 61d784c.

As discussed previously, count_sessions.inc is fragile, this guard can be easily bypassed by setting sleeps in the server. And we've seen such test failures in buildbot many times.

[gkodinov]

@vuvova seem to prefer to disable_warnings: 61d784c.

As discussed previously, count_sessions.inc is fragile, this guard can be easily bypassed by setting sleeps in the server. And we've seen such test failures in buildbot many times.

Disable_warning it is. I really think this is not the best option, but if it's popular, sure. The main point is to stabilize the test.