And what is your actual question?
What this message means?
If yes, here's the short explanation:
First PowerCenter issues a SELECT query for each source qualifier to the respective source database (no matter whether this is a "manually written" SELECT statement or a SELECT statement generated by PowerCenter itself). This point in time is logged in the session log with this RR_4049 message.
Now when the source DB either delivers the first record or the information "no data avaiable", you will get another message in the session log. The time difference between the RR_4049 and this second message is (roughly) the time that the source DB needs to prepare and execute the SELECT statement.
Finally, when the source DB deivers the last record to PowerCenter and indicates that this has been the last source record, PowerCenter will issue another message (something like "last record delivered by database at ...:...:...") in the session log.
Otherwise please explain in a bit more detail what exactly you want to know.