>I have noticed several log entries like:
>
>

>DBCC TRACEON 3604, server process ID (SPID) 59.
>DBCC TRACEOFF 3604, server process ID (SPID) 59.
>

>
>can someone tell me what this is and where do they come from?

Trace flags for performance tuning:

http://www.extremeexperts.com/SQL/Articles/DBCCTraceFlags.aspx

Trace flag 3604

"One of the most used trace flag. Trace flag 3604 sends trace output to the client. This trace flag is used only when setting trace flags with DBCC TRACEON and DBCC TRACEOFF. Trace flag 3604 was documented in SQL Server 6.5 Books Online and in SQL Server 7.0 Books Online, but was not documented in SQL Server 2000."