mysql56/wait__until__count__sessions_8inc_source.html

# include/wait_until_count_sessions.inc

#

# SUMMARY

#

#    Waits until the passed number ($count_sessions) of concurrent sessions or

#    a smaller number was observed via

#       SHOW STATUS LIKE 'Threads_connected'

#    or the operation times out.

#    Note:

#    1. We wait for $current_sessions <= $count_sessions because in the use case

#       with count_sessions.inc before and wait_until_count_sessions.inc after

#       the core of the test it could happen that the disconnects of sessions

#       belonging to the preceeding test are not finished.

#       sessions at test begin($count_sessions) =  m + n

#       sessions of the previous test which will be soon disconnected = n (n >= 0)

#       sessions at test end ($current sessions, assuming the test disconnects

#          all additional sessions) = m

#    2. Starting with 5.1 we could also use

#       SELECT COUNT(*) FROM information_schema.processlist

#       I stay with "SHOW STATUS LIKE 'Threads_connected'" because this

#       runs in all versions 5.0+

#

#

# USAGE

#

#    let $count_sessions= 3;

#    --source include/wait_until_count_sessions.inc

#

#    OR typical example of a test which uses more than one session

#       Such a test could harm successing tests if there is no server shutdown

#       and start between.

#

#       If the testing box is slow than the disconnect of sessions belonging to

#       the current test might happen when the successing test gets executed.

#       This means the successing test might see activities like unexpected

#       rows within the general log or the PROCESSLIST.

#       Example from bug http://bugs.mysql.com/bug.php?id=40377

#       --- bzr_mysql-6.0-rpl/.../r/log_state.result

#       +++ bzr_mysql-6.0-rpl/.../r/log_state.reject

#       @@ -25,6 +25,7 @@

#        event_time user_host ... command_type argument

#        TIMESTAMP  USER_HOST ... Query create table t1(f1 int)

#        TIMESTAMP  USER_HOST ... Query select * from mysql.general_log

#       +TIMESTAMP  USER_HOST ... Quit

#       ....

#

#       What to do?

#       -----------

#       <start of test>

#       # Determine initial number of connections (set $count_sessions)

#       --source include/count_sessions.inc

#       ...

#       connect (con1,.....)

#       ...

#       connection default;

#       ...

#       disconnect con1;

#       ...

#       # Wait until we have reached the initial number of connections

#       # or more than the sleep time above (10 seconds) has passed.

#       # $count_sessions

#       --source include/wait_until_count_sessions.inc

#       <end of test>

#

#       Important note about tests with unfortunate (= not cooperative

#       to successing tests) architecture:

#          connection con1;

#          send SELECT ..., sleep(10)

#          connection default;

#          ...

#          disconnect con1;

#          <end of test>

#       should be fixed by

#          connection con1;

#          send SELECT ..., sleep(10)

#          connection default;

#          ...

#          connect con1;

#          reap;

#          connection default;

#          disconnect con1;

#          <end of test>

#       and not only by appending include/wait_until_count_sessions.inc etc.

#

#

# EXAMPLE

#

#    backup.test, grant3.test

#

#

# Created:

#    2009-01-14 mleich

# Modified:

#    2009-02-24 mleich Fix Bug#43114 wait_until_count_sessions too restrictive,

#                                    random PB failures

#


let $wait_counter= 100;

if ($wait_timeout)

{

   let $wait_counter= `SELECT $wait_timeout * 10`;

}

# Reset $wait_timeout so that its value won't be used on subsequent

# calls, and default will be used instead.

let $wait_timeout= 0;

while ($wait_counter)

{

   let $current_sessions= query_get_value(SHOW STATUS LIKE 'Threads_connected', Value, 1);

   let $success= `SELECT $current_sessions <= $count_sessions`;

   if ($success)

   {

      let $wait_counter= 0;

   }

   if (!$success)

   {

      real_sleep 0.1;

      dec $wait_counter;

   }

}

if (!$success)

{

   --echo # Timeout in wait_until_count_sessions.inc

   --echo # Number of sessions   expected: <= $count_sessions   found: $current_sessions

   SHOW PROCESSLIST;

   --die Timeout in wait_until_count_sessions.inc

}