Sybase 12.4.2 manual Managing large buffer caches on HP, Controlling file system buffering, 437

CHAPTER 12 Managing System Resources

Managing large buffer caches on HP

On HP UNIX, start_asiq sets -iqsmemto 500 by default. This setting allows a total buffer cache size (i.e., main and temp caches combined) of 2GB.

If you need more than 2GB for buffer caches, and your system can accommodate a larger value, you must add unwired memory, by specifying -iqsmem. The value you specify on the command line overrides the start_asiq setting.

To get this much memory for
buffer caches	Set -iqsmem to this value
Up to 2000MB	provided by default by start_asiq
2200MB	600
2400MB	800
2600	1000
2800	1200
3000	1400

For example, the following settings are needed to allow buffer caches of 1600MB main and 800MB temp on HP UNIX:

SET OPTION "PUBLIC".MAIN_CACHE_MEMORY_MB = 1600

SET OPTION "PUBLIC".TEMP_CACHE_MEMORY_MB = 800

You must then restart the server with the following command:

start_asiq my_iqserver -iqsmem 800 my_iqdb

Controlling file system buffering

On Solaris UFS file systems and Windows NT file systems only, you can control whether file system buffering is turned on or off. Turning off file system buffering saves a data copy from the file system buffer cache to the main IQ buffer cache. Usually, doing so reduces paging, and therefore improves performance. However, you need to be aware of certain exceptions:

•If the IQ page size for the database is less than the file system's block size (typically only in the case in testing situations) turning off file system buffering may decrease performance, especially during multiuser operation.

•During loads, file system buffering may be helpful.

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