Percona Server is a MySQL build with additional modules from our compatriots Petr Zaitsev and Vadim Tkachenko and comrades. Its main feature is the default XtraDB storage engine. It differs from MySQL + InnoDB plugin with better performance and scalability, especially on modern multi-core servers. Also improved functionality - more stuff useful for optimization statistics and stuff. It maintains full compatibility with InnoDB tables, i.e. you can switch between InnoDB and XtraDB without any consequences (unless you use some XtraDB-specific features, like smaller page size).
XtraDB is based on InnoDB code, fully compatible with it, but has better performance due to the integration of patches from Google and Percona. In particular, in XtraDB improved memory handling mechanism, added support for multiple threads reading and writing, support for bandwidth management, the implementation of preemptive sampling data (read-ahead), adaptive checkpointing, improved I / O subsystem InnoDB, expanded scaling capabilities, finally appeared support for multi-threading and multi-processor, added additional features to collect additional data about the system and the analysis of statistics on them.
The most important and useful tool from those that develops Percona, besides XtraDB, in our opinion, is XtraBackup. It allows you to make backups of InnoDB and XtraDB databases right on the fly. Essentially, XtraBackup simply copies the current directory with the data while the server is on, which makes such a copy "faulty", and then restores the directory from the saved logs, just as MySQL would do during crash recovery. No database halts, except for a copy of MyISAM logs, hanging queries. Backup removal speed - up to several times faster compared to classic dumping.