MEMORY

SHMBASE

SHMVIRTSIZE* (kilobytes)

OLTP - Big Resident (buffers), small Virtual (SHMVIRTSIZE)
DSS - Small Resident, big Virtual
DSS may be up to 75% RAM if paging is not induced
DSS KEY FIELD

SHMADD (kilobytes) -

10 - 20% of SHMVIRTSIZE

SHMTOTAL

0 unlimited
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

if > 0, will enhance parallelization of index builds (which after 7.2 are always parallel to some degree)

MAX_PDQPRIORITY

100

DS_MAX_QUERIES

DS_TOTAL_MEMORY

DSS should be 90% of SHMVIRTSIZE

DS_MAX_SCANS

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.

 

 

Introduction

Main & CPU

Disk IO

Logging

Memory & DSS

Miscellaneous

Notes

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