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Scaling the memory size impacts the shared memory
usage which is adapted by the onconfig parameter BUFFERS.
When using the ext2 file systems on FCP disks, we
got the best results with the following rules:
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BUFFERS
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0.6 * memory size
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exceptions:
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1 CPU
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0.5 * memory size
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for 16GB and
Database cache hit ratio >99%
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0.75 * memory size
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further parameters:
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SHMVIRTSIZE
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0.2 * memory size
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SHMADD
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0.2 * memory size
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Note:
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The SHMVIRTSIZE was sized appropriately so that in any case no additional
segment was needed. Therefore it might be oversized.
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We locked all shared memory segments in storage. To achieve this, the specification
of the RESIDENT parameter with a value of 1 is not sufficient. It is necessary
to specify at least a value of 2 to fix the BUFFER pool segment and the
virtual segment.
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For buffer pools bigger than 4GB, Informix will allocate several segments.
The best way to lock all segments is to set the RESIDENT value to the number
of shared memory segments displayed from the LINUX command 'ipcs -m', as
far as they belong to the Informix database.
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For buffer pools bigger than 8GB you need the Informix version 9.40.FC3
or higher.
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