| Patrick,
the VLM feature in oracle allows you for two things:
- Big Oracle Blocks (BOB): up to 32 KB per block.
- Large number of database block buffers up to a limit beyond the
traditional 2 GB limitation. This is the parameter with the main impact on
the so called Large Shared Global Area (LSGA).
In datawarehouse environments, BOB is a must. However, depending on the
relative size of your database compared to the main memory you have
available, and also depending on the number of simultaneous users you are
going to support simultaneously, you may or may not benefit from the large
number of buffers.
If you do full scans mostly and your tables fit into main memory, VLM would
be fine, but don't forget to analyze your tables and specify the cost based
optimizer.
However, if many sorts or hash joins are to be performed, then you may
be interested in increasing the "sort-area-size" and/or the "hash-area-
size" which enlarges the per process PGA (Private Global Area), so nothing
to do with LSGA.
In the second case, quite common, the SGA should be sized so that the
smaller and more frequently used tables can be cached.
When many users with or without many parallel query servers want to access
the database, the VLM addressing and SMP capability of Digital UNIX can be
used here to support many concurrent processes (client, shadow or both).
I hope it helps,
Juli�n Rodr�guez
Digital Spain
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