Buffer Memory     (Overview)

DESCRIPTION
The "Buffer Memory" value represents the amount of shared memory allocated for
the VSAM file buffer pool. All Transaction Servers share this buffer pool. 
Sun MTP reads and writes database records from/to this area.  The buffer pool 
allows the database to be cached in memory, eliminating much physical I/O. 


VALUES
The size of the "Buffer Memory" is a configurable option in the VCT. The range 
is from 16 buffers (4096 bytes per buffer) up to a maximum of 9999. The VCT 
rejects any number outside this range. Sun MTPScan displays the size of "Buffer 
Memory" in K bytes. To verify that the numbers match up, divide the value by 4K 
to get the number of buffers.


INTERPRETATION
In general, a larger "Buffer Memory" allows for more of the database to be 
cached in memory. For some Sun MTP systems, however, this may not be true when 
the database is large and accessed randomly. In that case, the cache hit rate
is diminished and a large "Buffer Memory" is just wasted.


CONCLUSIONS
Sun MTP works most effectively with 200-500 buffers. When "Buffer Memory" is 
under 200 buffers, physical I/O increases to unacceptable levels because there 
aren't enough buffers to cache the I/O. When there are more than 500 buffers, 
the buffer search algorithms require excessive CPU usage.
