Re: coufused about ibtmp1

[eimmaa rose]

Hi Victor,

The documentation wording is a bit confusing because MySQL’s handling of temporary tables changed in recent versions. Here’s the concise explanation that matches what you observed:

User-created TEMPORARY TABLES (InnoDB)
Their data files live under #innodb_temp/ (controlled by innodb_temp_tablespaces_dir), so creating a temp table will update files like temp_XX.ibt there.

ibtmp1’s role
ibtmp1 is used for undo logs and some internal on-disk temporary structures. When you INSERT/UPDATE/DELETE on a temp table, the undo information is written to ibtmp1, which is why you see both temp_*.ibt and ibtmp1 modification times change.

So the correct summary is: data files for user temp tables → #innodb_temp; undo and internal temp activity → ibtmp1. Your tests align with this behavior.

If you want, I can post a shorter version of this for the forum or a more technical one with example commands (e.g., how to observe undo growth).

— Eimmaa Rose