We have compared network traffic used between Microsoft SQL Server and MySQL in a scenario where one event log entry is logged to a database. In this scenario EventSentry connected to the database server, transferred one event log entry (with approximately 200 characters), and disconnected from the database.
In this test we measured the following:
Microsoft SQL Server 2000 (without encryption):
~2.7kb for one event + TCP session setup
~1.6kb for each additional event
Microsoft SQL Server 2000 (with encryption):
~1.7kb for one event + TCP session setup
~1kb for each additional event
~10.5kb for one event + TCP session setup
~3.4kb for each additional event
As such, if you have limited bandwidth available and plan on transferring a significant amount of information over WAN links then MySQL and MSSQL will use less network traffic than Oracle.