Is it common practice to mix InnoDB and MyISAM tables on same server?

Question

I've got a single database of about 4.5GB running on a server with 8GB RAM. The vast majority of the tables are MyIsam (about 4.3GB), but I'm soon going to be converting some of them to InnoDB. (It's going to be a slow process, focusing on the most write-intensive tables at first).

Is there anything wrong with running a dedicated server where both types of storage engines exist?

Answer 1

There's nothing wrong with using multiple storage engines on the same physical machine, as long as you understand the pros and cons of each. There are performance considerations, feature limitations and use cases for all the plugin storage types.

For instance, if you have a small table that's 90% writes, you might choose MyISAM. If the data can be regenerated easily and it's a small table, say for queuing, you might choose Memory. If you have a table that's 90% reads, and the data has got to be there when you look for it, then you'd probably choose a storage engine that supports transactions and configurable atomicity, such as InnoDB. If you want accessibility through the file system w/o damaging data, you might choose CSV.

Nonetheless, you can safely use multiple storage engines within the same schema as well as the physical host.

Let me note though, that your buffers play a role in this whole mess. If you use both MyISAM and InnoDB, you will need to be careful that your key_buffer and innodb_buffer_pool do not contend. This will take careful planning on your part, but that's what we do.

Answer 2

I can't tell you if this is a common practice. I can say about my own experience.

I always use the best tool for the job, so I mix engines all the time. Most of my projects use MyISAM as the default engine.

When I need special features just available on InnoDB, I go for it.

When a table is mostly read-only, I choose Archive engine before I could blink.

Knowing that machine server has enough memory, all my temp data are store on Heap tables.

I saw in the past some slowdowns mixing MyISAM and InnoDB but this is not a specific MySQL problem. It's a design problem not seeming when you use just one engine. Actually using the wrong engine causes more slowdown doesn't matter if it is just MyISAM, just InnoDB or a mix of both. It's hard to define a formula to know when the slowdown would happen. Just actual tests could say it to you.

Of course, you couldn't preserve integrity and consistency mixing InnoDB and MyISAM on an unique query.

Answer 3

I try to avoid mixing MyISAM and InnoDB tables in the same database, but this is for sanity rather than practical reasons. However, I find it useful to have a database with MyISAM tables for fulltext search so I can run that on sites. Keeping it in a separate database with a foreign key for each entry makes it easy for any other developers working on the DB to see what's going on.