• Bill Qu's avatar
    Bug #15868071 USING SET GLOBAL SQL_LOG_BIN SHOULD NOT BE ALLOWED · 5693b1e4
    Bill Qu authored
    Normally, SET SESSION SQL_LOG_BIN is used by DBAs to run a
    non-conflicting command locally only, ensuring it does not
    get replicated.
    Setting GLOBAL SQL_LOG_BIN would not require all sessions to
    disconnect. When SQL_LOG_BIN is changed globally, it does not
    immediately take effect for any sessions. It takes effect by
    becoming the session-level default inherited at the start of
    each new session, and this setting is kept and cached for the
    duration of that session. Setting it intentionally is unlikely
    to have a useful effect under any circumstance; setting it
    unintentionally, such as while intending to use SET [SESSION]
    is potentially disastrous. Accidentally using SET GLOBAL
    SQL_LOG_BIN will not show an immediate effect to the user,
    instead not having the desired session-level effect, and thus
    causing other potential problems with local-only maintenance
    being binlogged and executed on slaves; And transactions from
    new sessions (after SQL_LOG_BIN is changed globally) are not
    binlogged and replicated, which would result in irrecoverable
    or difficult data loss.
    This is the regular GLOBAL variables way to work, but in
    replication context it does not look right on a working server
    (with connected sessions) 'set global sql_log_bin' and none of
    that connections is affected. Unexperienced DBA after noticing
    that the command did "nothing" will change the session var and
    most probably won't unset the global var, causing new sessions
    to not be binlog.
    Setting GLOBAL SQL_LOG_BIN allows DBA to stop binlogging on all
    new sessions, which can be used to make a server "replication
    read-only" without restarting the server. But this has such big
    requirements, stop all existing connections, that it is more
    likely to make a mess, it is too risky to allow the GLOBAL variable.
    
    The statement 'SET GLOBAL SQL_LOG_BIN=N' will produce an error
    in 5.5, 5.6 and 5.7. Reading the GLOBAL SQL_LOG_BIN will produce
    a deprecation warning in 5.7.
    5693b1e4
binlog_grant.test 1.7 KB