MEMORY
SHMBASE
SHMVIRTSIZE* (kilobytes)
 |
OLTP - Big Resident (buffers), small Virtual (SHMVIRTSIZE) |
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DSS - Small Resident, big Virtual |
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DSS may be up to 75% RAM if paging is not induced |
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DSS KEY FIELD |
SHMADD (kilobytes) -
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10 - 20% of SHMVIRTSIZE |
SHMTOTAL §
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0 unlimited |
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can be used to make Informix more polite reserving resources for other applications. I have also had to use this when a failing malloc panics oninit |
Monitoring: -g seg – One of the first things I check as consolidating shared memory segments can be huge bang for the buck.
Note that onmode -F (used to free memory segments) can cause system failures on an active system and should be avoided.
UNIX COMMANDS:
Sar -g 3 3 – will show paging activity
Vmstat
Notes:
To calc shared memory segments corresponding to a DB instance shmid – 52564801*.0001 = SERVERNUM
DSS PARAMETERS
PDQPRIORITY
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if > 0, will enhance parallelization of index builds (which after 7.2 are always parallel to some degree) |
MAX_PDQPRIORITY
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100 |
DS_MAX_QUERIES
DS_TOTAL_MEMORY
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DSS should be 90% of SHMVIRTSIZE |
DS_MAX_SCANS
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1048576 |
Notes:
Quantum = (PDQPRIORITY/100)*(DS_TOTAL_MEMORY/DS_MAX_QUERIES)
Each sort thread gets quantum/#sort threads memory
A users effective priority = (pdqpriority/100) * ( MAX_PDQPRIORITY/100) where pdqpriority is set by the environment variable or the SET PDQPRIORITY statement.
