Hi, Nirbhay!

On Jun 08, Nirbhay Choubey wrote:
> revision-id: 075233312cc5bc6c242f4629f8293d4c67937f02 (mariadb-10.1.14-10-g0752333)
> parent(s): c9f05974e618a869563f2360ef1ca910974a4f1c
> author: Nirbhay Choubey
> committer: Nirbhay Choubey
> timestamp: 2016-06-08 16:03:01 -0400
> message:
>
> MDEV-10161: wsrep_sync_wait not enabled when set to 1 in config file
>
> Since wsrep_sync_wait & wsrep_causal_reads variables are related,
> they are always kept in sync whenever one of them changes.
> Same is tried on server start, where wsrep_sync_wait get updated
> based on wsrep_causal_reads' value. But, since wsrep_causal_reads
> is OFF by default, wsrep_sync_wait's value gets modified and loses
> its WSREP_SYNC_WAIT_BEFORE_READ bit.
>
> Fixed by giving higher precedence to one that's explicitly set to
> a non-default value and later to wsrep_sync_wait in case both are
> set.
>
> diff --git a/sql/wsrep_mysqld.cc b/sql/wsrep_mysqld.cc
> index d0798ef..fffb0cc 100644
> --- a/sql/wsrep_mysqld.cc
> +++ b/sql/wsrep_mysqld.cc
> @@ -567,7 +567,39 @@ int wsrep_init()
>
>    wsrep_sst_auth_init(wsrep_sst_auth);
>
> -  wsrep_causal_reads_update(&global_system_variables);
> +  /*
> +    On server start, there is no way to detect whether the default value
> +    for a system variable was set explicitly by the user.
> +    Now, since wsrep_causal_reads & wsrep_sync_wait are used for same
> +    purpose, a rule of precedence must be defined to keep their values
> +    in sync. It goes as following:

This is wrong. First, in 10.1 there is a way to detect whether the value
was set by a user. I_S.SYSTEM_VARIABLES can show that.

But even if you'd detected that, it won't help you do distinguish
between

  mysqld --wsrep-sync-wait=1 --wsrep-causal-reads=0
  mysqld --wsrep-sync-wait=0 --wsrep-causal-reads=1

The only correct solution is to handle this in the mysqld_get_one_option
switch, updating the dependent option when one of these two is set.

Regards,
Sergei
Chief Architect MariaDB
and security@mariadb.org