If you’re running MySQL 5.7, you might have noticed the ibtmp1 file located in the datadir, and you might be wondering exactly what this file is.
In 5.7, InnoDB added a separate tablespace for all non-compressed InnoDB temporary tables. This new tablespace is named ibtmp1 and is located in the datadir by default.
“The new tablespace is always recreated on server startup. … A newly added configuration file option, innodb_temp_data_file_path, allows for a user-defined temporary data file path. For related information, see InnoDB Temporary Table Undo Logs.”
You can read that, and the full changelog entry, here: