The idea to use SSD/Flash as a cache is not new, and there are different solutions for this, both OpenSource like L2ARC for ZFS and Flashcache from Facebook, and proprietary, like directCache from Fusion-io.
They all however have some limitations, that’s why I am considering to have L2 cache on a database level, as an extension to InnoDB buffer pool.
Fortunately, there is a project in progress Flash_Cache_For_InnoDB by David which implements this.
David helped us to port his work to the latest Percona Server and you can get it from our launchpad Percona Server 5.5.28
I think that naming this as Flash_Cache is confusing due similarity to Flashcache from Facebook, so I prefer to name it as L2cache.
There is a quick benchmark on tpcc-mysql 2500W (250GB), I used
- data on RAID
- data on SSD (Intel SSD 910)
- data on RAID with L2 cache on Intel SSD 910, and size of cache is 150GB
As we see the result is quite good an promising, so I am going to continue to research on further integration with Percona Server.
Right now there are two challenging questions, which we need to resolve:
- Backup. In current state only mysqldump will work. To make backups with Percona XtraBackup we will need additional support of L2 cache in XtraBackup
- Recovery time. Right now if a crash happens, the cache is safe, but recovery time is on longer side, we need to see how it can be improved
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