InnoDB vs MyISAM
This pertains to MySQL 5.5
- InnoDB stores data in a file(s) called a tablespace. In newer versions of MySQL, you can store the data and indexes in separate files. MyISAM stores the data and indexes in two files (.MYD, .MYI). InnoDB is extremely critical about its tablespace and log files (They normally should be backed up together). You can’t just backup your data by copying files like you would with MyISAM. In some situations you can only restore a table to the server from which you backed it up!
- InnoDB are built on clustered indexes and uses MVCC to achieve high concurrency. This provides very fast primary key lookups. MyISAM doesn’t support transactions, FK contraints, or row-level locks. MyISAM uses shared and exclusive locks on the entire table. However, concurrent reads & inserts for new rows are allowed.
- InnoDB is crash safe (Assuming your flushes are truly durable on disk and not on some volatile cache). MyISAM is no where close to being crash safe. If you care about your data, use InnoDB. It might be OK to use MyISAM for read-only workloads.
- InnoDB will support full-text indexes in MySQL 5.6. MyISAM currently supports this feature. Normally these type of things should be offloaded to something like a Sphinx server.
- InnoDB repairs are reasonably fast. MyISAM is slow and you might not get all your data back. Eek.
- InnoDB requires a lot of memory (buffer pool). The data and indexes are cached in memory. Changes are written to the log buffer (physical memory) and are flushed every second to the log files (method depends on innodb_flush_log_at_trx_commit value). Having the data in memory is a huge performance boost. MyISAM only caches indexes (key_buffer_size) so that’s where you would allocate most of your memory if you’re only using MyISAM.
Overall InnoDB has a lot more intricacies but it’s worth learning about. In 99% of the cases, you should just stick to InnoDB unless you have a good reason not to.