A general guideline for cache sizes is 40% for the main buffer cache and 60% for the temp buffer cache. Start with this guideline, monitor server performance, then adjust the cache size as necessary.
The total memory used for Sybase IQ main and temporary buffer caches, plus Sybase IQ memory overhead, and memory used for the operating system and other applications, must not exceed the physical memory on your system.
For optimal performance, allocate as much memory as possible to the IQ main and temporary buffer caches. For example, if you have 4GB of physical memory on your machine available to Sybase IQ, you can split that amount between the main and temporary shared buffer caches.
Buffer cache size requirements depend on use. For maximum performance, change the settings between inserting, querying the database, and mixed use. In a mixed-use environment, however, it is not always feasible to require all users to exit the database so that you can reset buffer cache options. In those cases, you may need to favor either load or query performance.
These guidelines assume you have one active database on your system at a time. If you have more than one active database, you need to further split the remaining memory among the databases you expect to use.
On some UNIX platforms, you may need to set other server switches to make more memory available for buffer caches.