Subject: (I) Calculation for databases

I.EXM_SEGMENT_SIZE
===================

Example:
--------
DB-Size: 127 MB
process instances: 5000
22 process instance segments
about 250 instances per segment
average instance size: 20 kb

Conclusions:
------------
The maximum file size on AIX is 2 GB.
The maximum recommended database size to achieve good
performance on AIX is about 1 Gigabyte.

ObjectStore performance deteriorates nonlinear with
a segment number above 3000-4000.
Objectstore performance deteriorates with the number
of objects per segment.
You need to balance those facts and find a segment number
below 3000 without getting to much objects per segment.
This is easy for small databases (thus the default of 200kb
for EXM_SEGMENT_SIZE).

With a process instance size of 20 kb you can
achieve about 50 000 process instances in 1 Gigabyte.

Table for 50 000 process instances.

EXM_SEGMENT_SIZE    instances per segment     # segments
---------------------------------------------------------
200000 (default)       10                        5000
400000                 20                        2500
800000(recommended)    40                        1250

Recommendation:
---------------
go with a EXM_SEGMENT_SIZE=800000 because even if the database
grows to 2 GB (100000 process instances) the # of segments (2500)
then stays below the recommended limit of 3000.


II.EXM_PREALLOCATE_SEGMENT, EXM_NUMBER_OF_SEGMENTS,EXM_SEGMENT_STRATEGY


=======================================================================
Those only apply when multiple RTSRVs access the same database
(improve concurrency) and when the database keeps a constant size
and number of process instances.


III. OS_AS_SIZE
================
This has no performance impact.
If OS_AS_SIZE is set too low, you get an err_out_of_address_space
exception.
For FlowMark the default of 100000 was always high enough.
oscompact on the other hand required to increase the value up to 1GB
in some environments.
Only increase this value if you get the exception.


IV. OS_CACHE_SIZE
=================
Increasing the value improves performance until the whole working
set of a transaction fits into the cache IF the machine has enough
real memory to avoid paging/swapping.
We recommend to increase OS_CACHE_SIZE to a value of 1/4 to 1/3 of
real memory installed.

The working set of a transaction depends on the number of users
assigned and the complexity of your processes (e.g nested blocks,...).
The working set of FlowMark transactions should not exceed 100MB.
To really exactly tune this parameter one would have to measure the
working set of transactions in your environment using Objectstore
Performance expert.


V. OS_RELOPT_THRESH=0
=====================
This disables relocation optimization.
Relocation optimization is an algorithm ObjectStore uses to
optimize performance in some scenarios not relevant for FlowMark
ON COST OF ADDRESS SPACE CONSUMPTION.
Since Flowmark does not benefit from this optimization we want
to conserve address space and disable this.