repair by sorting?
mysqldump is disabling indexes, inserting the records, and re-enabling the indexes. This means it affects the entire table, including the many more records I expect are there based on the time.
Add --skip-disable-keys to the arguments for mysqldump and that should stop happening.
The mysqldump command will do three things to a table during the reload:
DISABLE KEYS;- multiple INSERTs...
ENABLE KEYS;
When you disable keys, it actually disables non-unique indexes.
Primary Keys and Unique Keys are loaded immediately.
Once ENABLE KEYS is started, all non-unique indexes are then build using 'Repair By Sorting';
If you bypass DISABLE KEYS and ENABLE KEYS, you will make things much worse, because the Primary Keys, Unique Keys, and Non-Unique Keys are built row by row and that's internally a messier operation for MySQL.
Since so little data is being added, doing --skip-disable-keys as 'Autocracy' suggested is both wise and concise.
BTW this only applies to MyISAM tables. InnoDB ignores DISABLE KEYS and ENABLE KEYS.