High ID (unique, auto increment) causes slow responses on PHP (MySQL)

 I've built a certain system where every time new user enters it creates a
"guest row" on "guests" table. he also gets an identifying cookie.

The table contains several fields, one of them is ID which is auto increment
and unique

When he does a certain action it gets recorded in the "done_action" table
with several fields on it, one of them is "guest_id" and his ID on it.


Problem is the guests table has about 30,000 rows (which means ID is high).

 I was wondering whether I should somehow change how the system works.

I've thought about couple of options

A weekly "cleanup" job. opens a table called "guests_tmp", *copies* all data
from guests to guests_tmp.

every row it copies it also changes the ID on the table done_action.

What do you  think?


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