Comments - Parallel Replication
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i understand this such way that if I give SELECT statement at Master it start threads to do SELECT at Master as well in Slave's.
No, this is completely wrong. Replication does not do anything with SELECT statements - only INSERT/UPDATE/DELETE.
I suggest reading up on a tutorial on MySQL replication to get a clearer picture.
I know Mysql replication, it's just replication,... nothing to do whit parallel !!!
I suggest you remove word parallel and change it Multimaster / Master / Master-slave - replication !!!
I suggest you get familiar whit parallel prosessing.
It could be possible,.... you could make SELECT that will be prossed by several threads and machines. That's parallel.
Your documentation is miss leading,... "f slave-parallel-threads is 0, then each slave setup will have one thread each to execute queries." What can be run in parallel
Currently the following things can be run in parallel on the slave:
Queries that are run on the master in one group commit. Queries that are from different domains. Queries from different masters (when using multi-source replication).
"the SQL threads will read ahead in the relay logs, queueing events in memory while looking for opportunities for executing events in parallel. The @@slave_parallel_max_queued variable sets a limit for how much memory the SQL threads will use for read-ahead in the relay logs looking for such opportunities."
knielsen is right. To repeat/rephrase: Parallel replication is replication with parallel execution of INSERT, UPDATE, and DELETE queries on slaves. It's the correct use of the word parallel. It is not multi-master or multi-source replication.
What you're doing is fixating on the word parallel, coming up with your own ideas about what the word means, and willfully ignoring the replication part.