While "AutoCommit" defaults to "true", there are cases where this default is not properly supported, and the perl/DBI programmer has to explicitly set it to "false" and then explicitly use the "commit" method as appropriate.

I ran across one such case when using Oracle 8.1.3 -- I found that a "select ... for update" would cause oracle to generate an error (don't remember what it said, exactly), unless AutoCommit was turned off. This caused some nasty diversions when we were migrating an app from Oracle 7.x, where there was no such problem.