In MySQL what does “Overhead” mean, what is bad about it, and how to fix it?

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It appears that the overhead is temporary diskspace that the database used to run some of the queries, so you should only worry if this gets really high.

You can compare ‘Optimizing the table’ with the defragmenting of your hard drive.

I quote:

Every database will, over time,
require some form of maintenance to
keep it at an optimal performance
level. Purging deleted rows,
resequencing, compressing, managing
index paths, defragmenting, etc. is
what is known as OPTIMIZATION in mysql
and other terms in other databases.
For example, IBM DB2/400 calls it
REORGANIZE PHYSICAL FILE MEMBER.

It’s kind of like changing the oil in
your car or getting a tune-up. You may
think you really don’t have to, but by
doing so your car runs much better,
you get better gas mileage, etc. A car
that gets lots of mileage requires
tune-ups more often. A database that
gets heavy use requires the same. If
you are doing a lot of UPDATE and/or
DELETE operations, and especially if
your tables have variable length
columns (VARCHAR, TEXT, etc), you need
to keep ‘er tuned up.

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