Solved

Configuring PID recycle pool on AIX

Posted on 2010-08-18
4
1,351 Views
Last Modified: 2013-11-17
We have a number of client sites running a custom application against our database, each with 500+ users. The database has associated with it a number of dedicated daemon processes, one of which is responsible for "cleaning up" any processes that exit unexpectedly, occasionally leaving record locks and shared memory which could compromise database integrity. The client's application typically launches many short-lived processes. As a result it is possible for a process to exit and before the daemon has a chance to detect and clean it up, the OS has re-assigned the PID to another process. Needless to say this can cause all manner of problems to the daemon and at its worst, force the daemon to exit and require a database shutdown.

We cannot reduce the sleep time of the daemon any further. The client has gone to 7-digit PIDs anticipating that this will increase the size of the PID pool available to it and hence reduce the chance of the problem arising, but this does not appear to have an basis since the problem still recurs from time to time.

Is there some way to configure the kernel to either:
1) increase the pool size? (there is a pool of PIDs isn't there?)
2) specify some delay period before the PID is re-used?
3) some other way to prevent the situation arising?

Many thanks in advance!

Mark
0
Comment
Question by:UnifySupport
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2
4 Comments
 
LVL 68

Assisted Solution

by:woolmilkporc
woolmilkporc earned 500 total points
ID: 33473084
Hi,
I guess your database is Universe?
If so, going to 7-digit PIDs is a mandatory approach. Are you sure that this configuration is actually in effect?
In AIX the PID assignment is somewhat unpredictable, to avoid creating a covert channel (allowing for conclusion on the OS by analyzing the sequence of PIDs used).
AIX PIDs are a combination of the PSLOT number (which can be reused immediately) and a Generation Count (max. 4096 afaik) which should prevent PIDs from being reused too rapidly. AIX PIDs are always even (except for 1, "init").
There is no "pool" of PIDs. You can't influence the creating or reusing of PIDs in AIX.
Did you talk to your database provider? I think there is nothing you can do on the AIX side.
 wmp
0
 

Author Comment

by:UnifySupport
ID: 33473569
It's actually a Unify database, I am a support engineer for Unify Corporation and the client has implemented 7-digit PIDs. However, I do not know whether they have max'd the generation count. I remember in a recent googling odyssey seeing PLSOT mentioned - there was also a second configuration variable involved but its name escapes me at the moment and I forgot to bookmark the site :(

Can you please tell me how I can determine what the generation count would be? I'm also guessing that 4096 (which does seem to ring a bell as the maximum value which can be ascribed) is not the default setting - yes?

Cheers,
Mark
0
 
LVL 68

Accepted Solution

by:
woolmilkporc earned 500 total points
ID: 33473830
4096 for Generation Count seems unchangeable. At least I have no idea at all where this could be done. If it were a tunable value it should appear with  "schedo -a" ("schedo -F -a" in AIX 6) or should be referenced by an environment variable. Both is not the case, as far as I can see.
This is the appropriate reference -
http://publib.boulder.ibm.com/infocenter/aix/v6r1/index.jsp?topic=/com.ibm.aix.prftungd/doc/prftungd/summ_tun_params.htm 
You cam check whether it's actually 4096 -
- Take some unique, well-known process, like "cron"
- Issue "ps -ef | grep cron" and note the PID
- Issue "pstat -a | grep cron" and note the PSLOT (1st column)
- Perform an integer divide "PID / 4096" e.g. with ksh "echo $((PID/4096))"
- You will get PSLOT, q.e.d.
There is no other value besides the calculated PSLOT and the fixed Generation Count 0-4096 step 2, afaik.
 wmp
0
 

Author Closing Comment

by:UnifySupport
ID: 35404276
Thank you, and please forgive the delay in completing this!
0

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
AIX Server 10 95
Control Number of Log Files -Perl 7 102
add some character at the end of line in vi 7 135
lunix and unix command 21 154
My previous tech tip, Installing the Solaris OS From the Flash Archive On a Tape (http://www.experts-exchange.com/articles/OS/Unix/Solaris/Installing-the-Solaris-OS-From-the-Flash-Archive-on-a-Tape.html), discussed installing the Solaris Operating S…
Introduction Regular patching is part of a system administrator's tasks. However, many patches require that the system be in single-user mode before they can be installed. A cluster patch in particular can take quite a while to apply if the machine…
Learn how to navigate the file tree with the shell. Use pwd to print the current working directory: Use ls to list a directory's contents: Use cd to change to a new directory: Use wildcards instead of typing out long directory names: Use ../ to move…
In a previous video, we went over how to export a DynamoDB table into Amazon S3.  In this video, we show how to load the export from S3 into a DynamoDB table.

734 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question