Matt, from the ever excellent MySQL Performance Blog, decided to run a test using a simple scenario drawn from his client experience in the gaming space. The scenario: read a row based on a primary key, update the row, write it to disk, and use the row to lookup another row. Matt ran three different tests explained in a series of three different articles: MySQL and MySQL + Memcached, Memcached Only, and Tokyo Tyrant.
The lovingly compiled details along with many cool graphs are in the articles, but in general the lessons learned are:
- When memcached has enough memory (so records being accessed are in RAM), memcached + MySQL can provide a 10x performance boost over MySQL alone. When the RAM is too small and hot records, those being accessed a lot, aren't in RAM, or perhaps applications are doing a sequential scan of a table and the entire table isn't cached, then memcached won't be the big bang improvement you may be hoping for.
- When the database is removed and memcached serves both reads and writes the result is a 2.5x more performance over MySQL + memcached and 100x over MySQL alone. Warning warning: as you read on the memcached email list a 1000 times, memcached is just a cache, not a persistent store, you will lose data, so don't try this at home.
- Tokyo Tyrant is a disk based key-value store. Tyrant was nearly 2x faster than MySQL + memcached and about 20% slower than a memcached only solution. Keep in mind one concern about Tyrant is that it is not distributed, it's not a scale-out solution, so it will face sharding issues similar to MySQL. It also flushes data to disk periodically which leaves an open data loss hole and variable performance during syncs.
Matt is careful to say he is not trying to pick a winner. His purpose is to get you to take a look at your application and be open to which solution will work best for your particular problem. There are options out there now. Ask yourself: Is keeping data in the database really necessary? Or is there a different tool for the job that may work better than that trusty old hammer?
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