Date:         Wed, 9 Aug 1995 10:56:05 EDT
Reply-To:     The NOMAD2 Discussion List
Sender:       The NOMAD2 Discussion List
From:         "Walter H.Horowitz"
Subject:      VM Storage sizes for shared database servers
Comments: To: Nomad2 Discussion List
          <NOMAD2-L%TAMVM1.TAMU.EDU@sna_norwalk_2.alsys.com>

The following was provided by Lloyd Fuller:

Unlike VM/HPO (or VM/SP), VM/ESA doesn't take any additional real memory
for larger virtual machines (except during actual use of the memory)
except at "break" points.  Those "break" points are at 32MB multiples.
Under VM/ESA, page tables are pageable (they weren't with HPO/SP), and
32MBs worth fit in one set of segment tables.

Hence it costs no additional real memory until a virtual machine exceeds
32MB _UNLESS_ the memory is used.  So I have been suggesting that you
make shared database servers be 32MB in size.

Now, will the memory be used and how?  With version 5.50 and newer, BTREE
buffers are above 16MB line in VM.  With 6.00 and newer, TYPE STANDARD
can make bigger blocks and/or use the other SCHEMA options to cause more
buffers.  This allows more of the database to stay resident in memory and
reduces I/O and can reduce paging.  If we have the data in our buffers in
memory, we don't have to ask CMS for it.

In addition to buffers, NOMAD puts some control storage and all window/
screen buffers above 16MB when possible.  Servers typically won't have
window/screen buffers, but they do use the control storage above 16MB.

Some more information about running under VM/ESA:

1.  The clients don't have to be running in XA mode for the server to run
XA.  The clients can be, or some or all can be running in 370 virtual
not necessarily the same _COPY_.  In other words, if you have several
XA servers, you can load one copy of NOMAD above 16MB for the servers,
and another copy for the clients that can still be running in 370.  Or,
if many of the clients are also running XA, they can also use the copy
above 16MB.

2.  If you are running VM/ESA version 1.1 or newer, _AND_ running on
ES/9000 hardware, you can use DATASPACEs.  NOMAD will use dataspaces for
shared database servers for LOOKUP tables.  It knows to do this when the
server is running in an XC virtual machine.  Two directory statements are
necessary for the server (documented in the VM Installation Guide for
6.00).  When asked to load a LOOKUP table, the server will attempt to
create a dataspace (or use one if it is already there).  The information
for the table will be loaded into the dataspace, and shared with all
clients.  The clients that are running in XC virtual machines will do the
lookup directly without talking to the server further (barring any updates
to the table).  Other clients still talk to the server for lookup.
Walter H. Horowitz - email whh@dart.thomsoft.com
Thomson Software Products - (203) 845-5025
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