Using MyISAM for reading and InnoDB for writing data I read many articles about comparisons of MyISAM and InnoDB from performance point of view and I decided to use MyISAM for reading data and InnoDB for writing data.

I want to use two structure like an image below. Two same (synchronized) databases but different table engines.



What is your suggestions about this structure?
What are disadvantages of this design?
I recommend against using this. Consider:

This would only be of some advantage if on two separate servers (no point in mixing both on same MySQL server, naturally, since reads &amp; writes will take place on both)

Which means you would follow RolandoMySQLDBA's advice, and set up an InnoDB master with MyISAM slave.

Do you have foreign keys on your InnoDB tables? If so, you're into integrity issues. If you happen to have ON DELETE CASCADE or ON DELETE SET NULL - prepare for bad news -- the cascading will not propagate on the slave. See: Impact of foreign keys absence on replicating slaves

OK, so maybe it's just this one table, and no foreign keys. But then you get to inherit all of MyISAM's other disadvantages, such as the likely possibility of not being able to recover from crash. Transactions won't work; the slave may find itself trying to execute queries on a table that hasn't really recovered from a crash; contains incorrect data. You may run into replication failures.

Phil's comment is also very valid: by synchronizing the tables you actually mean any write to your InnoDB table must propagate to your MyISAM table. This means same amount of writing.

If you are willing to relax some constraints, such as only batching (somehow?) the writes to the slave every once in a while, then that makes somewhat more sense.

So, in general, while the solution could work, you would have a constant headache to take care of.