Mysql partitioning

Partitioning is a write-optimization.

A partitioned table's contents are stored in different locations (ex. different servers).
A partitioning key is passed to a function to determine which partition a row or column should belong to.

Partitions must share the same storage-engine

Frequently a globally relevant identifier is used as the partitioning key (ex. a user).
then all of the rest of their data (ex. comments, projects, posts, ..) are stored on the same database instance.

Partition Methods

horizontal:  rows are partitioned
vertical:    cols are partitioned

Partition Introspection

EXPLAIN PARTITIONS SELECT * FROM users;  # list partitions, partition-key for query