• petr/cps@mysql.com/owlet.'s avatar
    Fix Bug #18559 "log tables cannot change engine, and · be2ce261
    petr/cps@mysql.com/owlet. authored
                    gets deadlocked when dropping w/ log on"
    
    Log tables rely on concurrent insert machinery to add data.
    This means that log tables are always opened and locked by
    special (artificial) logger threads. Because of this, the thread
    which tries to drop a log table starts to wait for the table
    to be unlocked. Which will happen only if the log table is disabled.
    Alike situation happens if one tries to alter a log table.
    However in addition to the problem above, alter table calls
    check_if_locking_is_allowed() routine for the engine. The
    routine does not allow alter for the log tables. So, alter
    doesn't start waiting forever for logs to be disabled, but 
    returns with an error.
    Another problem is that not all engines could be used for
    the log tables. That's because they need concurrent insert.
    
    In this patch we:
    (1) Explicitly disallow to drop/alter a log table if it
        is currently used by the logger.
    (2) Update MyISAM to support log tables
    (3) Allow to drop log tables/alter log tables if log is
        disabled
    At the same time we (4) Disallow to alter log tables to
    unsupported engine (after this patch CSV and MyISAM are 
    alowed)
    Recommit with review fixes.
    be2ce261
log.h 19.1 KB