* The ability to tune various parts of innodb that were originally designed to perform well on regular disks - those with fast sequential access, slower random access, and no real wear considerations. See http://www.percona.com/doc/percona-server/5.1/scalability/in...
I haven't looked at MariaDB 5.5 to see how it compares to Percona Server 5.5. I put Percona Server into production last fall and MariaDB was still at 5.3 at the time.
* You can put the innodb doublewrite buffer on your spinning disks - that's the best place for it since it's heavy sequential writes. See section 2.2.2 here http://yoshinorimatsunobu.blogspot.com/2009/05/tables-on-ssd...
* The ability to tune various parts of innodb that were originally designed to perform well on regular disks - those with fast sequential access, slower random access, and no real wear considerations. See http://www.percona.com/doc/percona-server/5.1/scalability/in...
Here's a recent post from Percona showing MySQL vs Percona server on an Intel 320 SSD: http://www.mysqlperformanceblog.com/2012/02/23/percona-serve...
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MariaDB is pretty nice too. Their team has introduced some sorely needed query optimizations (http://kb.askmonty.org/en/what-is-mariadb-53/#subquery-optim...) and it does include Percona's XtraDB.
I haven't looked at MariaDB 5.5 to see how it compares to Percona Server 5.5. I put Percona Server into production last fall and MariaDB was still at 5.3 at the time.