Shared memory issue::shared memory segments can not be allocated

by on February 16, 2010

SQL1084C Shared memory segments cannot be allocated

Have you seen above message anytime? It is annoying when you see this message.Basically first thing you can try is changing instance_memory and database_memory

Important kernel parameters to be considered here are shmmax and shmall.Shmmax is the maximum size of a shared memory segment and shmall is the maximum allocatable shared memory(sum of shared mem segments should be equal or less than this).Recommended value for shmmax is setting it equal to the RAM and for shmall it is 90% of physical memory

ipcs -l is the command to check the values of these kernel parameters

—— Shared Memory Limits ——–
max number of segments = 4096 // SHMMNI
max seg size (kbytes) = 32768 // SHMMAX
max total shared memory (kbytes) = 8388608 // SHMALL
min seg size (bytes) = 1

Sometimes you need to increase the value of shmmax to accomodate bigger segment or even increase shmall value to help more overall shared memory.

How do we map shared memory on the box with shared memory parameters on the database and instance??

We use db2pd -memsets,db2pd -mempools to look at the shared memory segments allocated and we try to map it to the original values on the box.My next blog post will reveal the mapping mechanism and the usage of db2pd -memsets,db2pd -mempools commands

{ 1 comment… read it below or add one }

Matilda September 16, 2011 at 4:08 pm

I was really confused, and this answered all my qtuesoins.

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