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Shared memory segment with 0 attaches

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Juan Canjura
Advisor

Shared memory segment with 0 attaches

Hi,

I just run a sys_check on a 3-node Tru64 Cluster and found some messages similar to this one:

Operational: Shared memory segment with 0 attaches ( 5243056 ).
This is should be investigated. This may be normal, or may mean shared memory was not properly released.

I've been searching for some light on this but couldn't anything yet. What does this mean? (or better) is there any way to find out if that could be a performance issue?

Thanks in advance.

Juan
3 REPLIES
Victor Semaska_3
Esteemed Contributor

Re: Shared memory segment with 0 attaches

Juan,

I get those messages all the time when I run sys_check. Check with the ipcs command like this:

# ipcs -bom

Shared Memory:
T ID KEY MODE OWNER GROUP NATTCH SEGSZ
m 0 0x435dce60 --rw-rw-rw- root system 1 8024
m 1 0x615d045c --rw------- root daemon 0 57776

The NATTCH column is the no. attached. I get the error message because of the 2nd one. Don't know why it's there, I simply ignore them.

Vic


Vic
There are 10 kinds of people, one that understands binary and one that doesn't.
Ivan Ferreira
Honored Contributor
Solution

Re: Shared memory segment with 0 attaches

Shared memory is used for process communications. Normally, databases make extensive use of shared memory.

When the database starts, or a process that uses shared memory start, it creates the shared memory segment. Normally, one or more process are attached to the shared memory segment to exchange information.

There could be the case, that a process creates a shared memory segment, but when it ends, does not closes the shared memory segment created. If is not used, then is consuming memory without needs.

You can view the CPID/LPID to identify the current and last process ID that used the shared memory segment. You can also identify the creator by looking at the CREATOR CGROUP fields.
Por que hacerlo dificil si es posible hacerlo facil? - Why do it the hard way, when you can do it the easy way?
Juan Canjura
Advisor

Re: Shared memory segment with 0 attaches

Fair enough, thank you both.

Juan