mysql_deadlock_restart_transaction

[pikiou]

I playtested my game with someone on another computer, and each time I got a white screen with this message:

Code: Select all

Sorry, an unexpected error has occured ...

mysql_deadlock_restart_transaction

#0 /home/pikiou/gearnpiston/gearnpiston.game.php(783): APP_DbObject::DbQuery('REPLACE propert...')
#1 /home/pikiou/gearnpiston/gearnpiston.game.php(185): Gearnpiston->saveProperties()
#2 /var/tournoi/release/tournoi-130118-1659-gs/www/game/module/table/table.game.php(74): Gearnpiston->getAllDatas()
#3 /var/tournoi/release/tournoi-130118-1659-gs/www/view/common/game.view.php(176): Table->getAllTableDatas()
#4 /var/tournoi/release/tournoi-130118-1659-gs/www/view/common/game.view.php(135): game_view->post_generate()
#3 /var/tournoi/release/tournoi-130118-1659-gs/www/view/common/game.view.php(176): Table->getAllTableDatas()
#4 /var/tournoi/release/tournoi-130118-1659-gs/www/view/common/game.view.php(135): game_view->post_generate()
#5 /var/tournoi/release/tournoi-130118-1659-gs/www/view/common/ebg.view.php(23): game_view->generate_content(Array)
#6 /var/tournoi/release/tournoi-130118-1659-gs/www/include/webActionCore.inc.php(178): ebg_view->generate(Array)
#7 /var/tournoi/release/tournoi-130118-1659-gs/www/index.php(126): launchWebAction('gearnpiston', 'gearnpiston', '__default', false, false, NULL, true)
#8 {main}

A deadlock happens when two scripts try to modify the same table at the same time and the mysql server is configured to only allow one at a time.
A refresh did the trick, but I'm wandering: will this only happen in the studio or do I have to loop repeat all my DB queries just in case?

[Alkazar]

Is your table InnoDb or MyIsam(not sure what is the default) ?
If it's not, it should be Innodb.
In InnoDb, a deadlock happens if a user 1 locks a row X in table A , user 2 locks a row Y in table B(could be the same table) and then 1 tries to get a lock on row Y of table B (no deadlock yet), and 2 tries to get a lock on row X of table A. Do you see if it can happen in your game logic ?
Anyway, deadlocks are resolved automatically, and the only thing you should do try to avoid succession of queries which could end in deadlocks, but never retries the query on it's own.

[pikiou]

Table engine was correctly InnoDB but your explanation made it clear what was wrong, thanks a lot!
Two users were updating the same set of rows but in a random order, hence the mutual block.