When you add memory, you increase cache to maximize the capability of the CPUs. This is helpful when CPUs are processing faster than the disk contents can be read into memory (that is, when the system is I/O-bound).
The following table lists reasons to add more memory.
|Add vprocs to existing nodes||Each vproc consumes 32 MB of memory. When you add vprocs to existing nodes, you probably should add memory.
Additional vprocs can substantially reduce free memory, which can cause more I/Os because the system can cache fewer datablocks.
|Excessive paging/swapping (thrashing)||More memory means that more code and data can be cached, achieving less I/O for paging and swapping.|
|Tables in memory||Increased memory may reduce I/O by accommodating:
I/O can be affected by the size of data blocks. See the DATABLOCKSIZE option for the CREATE TABLE statement in SQL Data Definition Language.