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

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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!

The 5102 trace flag prevents engine 0 from running any non-affinitied tasks. Normally, this forces engine 0 to perform Network I/O only. Applications with heavy result set requirements (either large results or many connections issuing short, fast requests) may benefit. This effectively eliminates the normal latency for engine 0 to complete running its user thread before it issues the network I/O to the underlying network transport driver. If used in conjunction with the 5101 trace flag, engine 0 would perform all Disk I/O and Network I/O. For environments with heavy disk and network I/O, engine 0 could easily saturate when only the 5101 flag is in use. This flag allows engine 0 to concentrate on I/O by not allowing it to run user tasks. To force task affinity off engine 0, start ASE with the 5102 Trace Flag.

Your errorlog will indicate the use of this option with the message:
I/O only enabled for engine: 0

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