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What is Trace Flags -- 5101 and 5102 in Sybase?



Normally, each engine issues and checks for its own Disk I/O on behalf of the tasks it runs. In completely symmetric operating systems, this behavior provides maximum I/O throughput for ASE. Some operating systems are not completely symmetric in their Disk I/O routines. For these environments, the server can be booted with the 5101 trace flag. While tasks still request disk I/O from any engine, the actual request to/from the OS is performed by engine 0. The performance benefit comes from the reduced or eliminated contention on the locking mechanism inside the OS kernel. To enable I/O affinity to engine 0, start ASE with the 5101 Trace Flag.

Your errorlog will indicate the use of this option with the message:

Disk I/O affinitied to engine: 0

This trace flag only provides performance gains for servers with 3 or more dataserver engines configured and being significantly utilized.

Use of this trace flag with fully symmetric operating systems will degrade performance!

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