Question

Whatever changes made to the MySQL database, are those changes readable within the same transaction? Or should I commit the transaction to read the changes?

I could easily test this. But putting a question in SO brings up a lot of good suggestions. Thanks for any input.

Answer 1

Assuming you’re using InnoDB, the answer to your first question is generally yes, implying the answer to your second is generally no.

By default MySQL’s InnoDB uses a technique called consistent non-locking reads:

The query sees the changes made by
transactions that committed before
that point of time, and no changes
made by later or uncommitted
transactions. The exception to this
rule is that the query sees the
changes made by earlier statements
within the same transaction.

That being said, there’s a lot of stuff to know about transactions. You can change the isolation level of a transaction in order to control the transaction results more thoroughly.

The chapter on the InnoDB Transaction Model is a great place to start.