Sachin Setiya <sachin.set...@mariadb.com> writes: > To my surprise slave_parallel_mode is replication channel specific , > while slave_parallel threadsis a global variable, Why So ?
There is a single pool of worker threads, to enable threads to be shared among multi-source connections - for example so all threads can work on one busy connection while another is idle. That is why slave_parallel_threads must be global. In contrast, it is perfectly possible to run one multi-source connection in conservative mode, and another in optimistic, for example. > And in mariadb documentation I was unable to find which variable is > replication channel specific and which variable is global one. Hm, if it's not documented that slave_parallel_mode is per-channel, that is unfortunate (this is something that was introduced for 10.1). > Yep, because if there is DDL statement or non transnational statement > it is executed alone. > So no need of mutex. Right, but you still need _some_ way to synchronise multiple threads incrementing the counter simultaneously (it is perfectly possible for two non-transactional event groups to execute concurrently in conservative mode, for example). >> The name "statements" is very confusing here, since you are counting event >> groups, not individual statements. >> > Changed It to event total_ddl_events , total_non_trans_events It's not individual events. It is "event groups", though this is mostly a terminology internally in the source code. The term "transaction" is unfortunate for something that is non-transactional. The name "event group" is also bad, as it is unfamiliar to users, I think. Maybe "total_ddl_events" is ok. I think in most cases only one statement at a time can be in an event group, when it is non-transactional or DDL. Though multiple binlog events will be involved for the single statement. >From this, _statement might also be ok, though it is somewhat unfortunate in case of row-based replication, where no SQL statements are involved at all on the slave. So baring better ideas, I guess *_events is ok, just be sure to make it clear in the documentation exactly what is counted. - Kristian. _______________________________________________ Mailing list: https://launchpad.net/~maria-developers Post to : maria-developers@lists.launchpad.net Unsubscribe : https://launchpad.net/~maria-developers More help : https://help.launchpad.net/ListHelp
