Re: MySQL DB Size increase after partitioning

[Rick James]

Virtually every ALTER involves copying the entire table over. This means that briefly that twice as much disk space will be used.

If you have innodb_file_per_table = OFF and you are using InnoDB, then this "copy" of the table will exist in ibdata1. ibdata1 never shrinks. (This issue is a common one in the InnoDB forum.)

If you have innodb_file_per_table = ON and you are using InnoDB, then there will be new files, one per partition. These files will probably be allocated 8MB at a chunk. So, lots of partitions could lead to lots of free space 'wasted' in each partition.

If the table (pre- or post-PARTITION) had been MyISAM, the old copy probably would have been completely returned to the OS.

I fear you are stuck with a 375GB disk footprint, unless you want to go through an arduous procedure to free the extra space.