Specifies the size of the main shared buffer cache.
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Can be set only for the PUBLIC group. Requires DBA permissions to set the option. Shut down and restart the database server for the change to take effect.
This option sets the size of the main shared memory buffer cache for the database. Sybase recommends that you do not use this option; instead, set the main buffer cache size with the -iqmc server option.
On 64-bit systems, you can allocate as much physical memory as you have to IQ buffer caches; however, for values greater than 4GB, you must use the server options -iqmc and -iqtc to set main and temporary buffer cache sizes. On 32-bit systems, the operating system limits the amount of memory you can allocate. See the Sybase IQ Installation and Configuration Guide for your platform for details.
For any active database, the default main buffer cache size of 16MB is too low. For optimal performance, allocate as much memory as possible to the IQ main and temporary buffer caches. For example, if you have 4GB of shared memory on your machine available to Sybase IQ, you can split that amount between the main and temporary shared buffer caches.
When setting the main cache size you must consider many factors, including total physical memory, swap space, memory for the temporary buffer cache, your mix of query and load processing, as well as memory requirements of the operating system and other applications on the machine.
For information about setting buffer cache sizes, see Chapter 5, “Managing System Resources” in the Sybase IQ Performance and Tuning Guide.
