Commit Transaction Command

The debug logs seem a little confusing. On sending a query something like
this will show up:

DEBUG: StartTransactionCommand
LOG: query: select * from blah;
DEBUG: ProcessQuery
DEBUG: CommitTransactionCommand

This is with auto commit off. My first reaction on seeing this was the auto
commit setting must not work. Then I noticed that most things, even "begin"
and "commit" commands entered via the query interface in psql were wrapped
with the same "DEBUG" output. And finally I did some testing and found that
transactions did in fact work correctly.

I am hoping that someone can enlighten me as to what this DEBUG output
actually indicates.

Running version 7.3.5.

Thanks,

Jim Wilson