MySQL: Truncate Table within Transaction?

Question

I have an InnoDB table that needs to be re-populated every ten minutes within anywhere from 60k to 200k records. Our approach up to this point has been as follows:

1. Turn off Autocommit
2. Truncate the table
3. Perform Select Queries & additional Calculations (using PHP)
4. Insert new records
5. Commit

After the Truncate operation is performed though, the data is immediately deleted, and is no longer available from the User Interface. To our users, this has been pretty disconcerting, even though within about 30 seconds or so the script encounters the Commit operation and the table is repopulated.

I thought that perhaps I could wrap the whole operation, including the Truncate, in a transaction, and that this might cut down on the length of time during which the table appears empty to users. So I changed SET AUTOCOMMIT=0 to START TRANSCATION.

Yikes! This had the opposite of the desired effect! Now the TRUNCATE operation still occurs at the beginning of the script, but it takes much longer to actually execute the INSERT operations within the transaction, so that by the time the COMMIT operation takes place and the data in the table is available again, it has been nearly ten minutes!

What could possibly cause this? Truthfully, I wasn't expecting any change at all, because I was under the impression that initiating a transaction basically just turns off Autocommit anyway??

question from:https://stackoverflow.com/questions/5972364/mysql-truncate-table-within-transaction

Answer 1

A better way to accomplish this might be to insert the data into a new table, and then use rename on both tables in order to swap them. A single rename is all that's needed for the swap, and this is an atomic action, which means the users won't even be able to detect that it happened, except for the new data showing up. You can then truncate/delete the old data.