Size              (Recovery)

DESCRIPTION
"Size" indicates the size of the recovery file as specified in the Sun MTP VSAM
Configuration Table (VCT).


VALUES
"Size" displays the size in terms of blocks, not bytes. Each block contains the
same number of bytes as the VSAM block size for the system.  The default VSAM
block size is 4K.  However, the block size can be 4, 8, 16, or 32K. If recovery 
is not active by request, "Size" shows nothing. If a "Filename" has been 
specified in the VCT, but the "Size" is less than one hundred blocks, the
datapoint displays 'Not Enough' instead of the number specified in the VCT.


INTERPRETATION
The optimum recovery file "Size" file depends on the recovery activity generated
by applications running within a Sun MTP system. Logically, Sun MTPScan treats the 
recovery file as a circular file. The actual file is a fixed "Size". Sun MTP must
abort a transaction when the logical tail of the file catches up with the head 
in order to safely provide data integrity. The value of "Last Wrap" gives an 
idea of how often this happens. When "Last Wrap" continues to change, recovery 
file "Size" is a limiting factor in system performance and the "Size" should be 
increased.

One rule of thumb for calculating a working recovery file "Size" is to base the
"Size" on the activity of the most write-heavy transaction. Each write to a 
database may generate an accompanying before image to the recovery file (if a
successive write is to a different record). Multiply the number of these writes
by the number of Transaction Servers. Then multiply that number by the average
record size. Use the result as an initial recovery file "Size" (remember to 
transform the "Size" from bytes to blocks) and adjust when "Last Wrap" sees too 
much activity. 

Note that you must further increase the "Size" of the recovery file to take into
account batch jobs that also require recovery file space.


CONCLUSIONS
If the "Size" is less than one hundred blocks, Sun MTP does not perform VSAM 
recovery. When this is the case, Sun MTPScan displays 'Not Enough' for "Size". If 
you want recovery, change the number of blocks in the VCT, write the changes, 
and restart the Sun MTP system. Then consult the Recovery Screen to make sure 
recovery is working as desired.
