Does MySQL (MyISAM) fill table holes in a multirow insert?

Question

I'm working on a project for which I need to frequently insert ~500 or so records at a remote location. I will be doing this in a single INSERT to minimize network traffic. I do, however, need to know the exact id field ( AUTO_INCREMENT ) values.

My web searches seem to indicate I could probably use the last_insert_id and calculate all the id values from there. However, this wouldn't work if the rows get ids that are all over the place.

Could anyone please clarify what would or should happen, and if the mathematical solution is safe?

Answer 1

A multirow insert is an atomic operation in MySQL (both MyISAM and InnoDB). Since the table will be locked for writing during this operations, no other rows will be inserted/updated during it's execution.

This means IDs will in fact be consecutive (unless auto-increment-increment option is set to something different than 1

Answer 2

Auto increment does exactly that, it auto-increments - ie each new row next the numerically next ID. MySQL does not re-use IDs of rows that were deleted.

Your solution is safe because write operations aquire a table lock, so no other inserts can happen while your operation completes - so you will get n contiguous auto-increment values for n inserted rows.