[ClusterLabs] Antw: Re: Antw: Re: Using different folder for /var/lib/pacemaker and usage of /dev/shm files

[Ulrich Windl]

>>> Ken Gaillot <kgaillot at redhat.com> schrieb am 17.05.2016 um 16:53 in Nachricht
<573B3074.1040305 at redhat.com>:
> On 05/17/2016 04:07 AM, Nikhil Utane wrote:
>> What I would like to understand is how much total shared memory
>> (approximately) would Pacemaker need so that accordingly I can define
>> the partition size. Currently it is 300 MB in our system. I recently ran
>> into insufficient shared memory issue because of improper clean-up. So
>> would like to understand how much Pacemaker would need for a 6-node
>> cluster so that accordingly I can increase it.
> 
> I have no idea :-)

A related question would be: What's in those segments? "strings" indicates that there is a lot of XML in those segments, and I as programmer who's first computer had 400 bytes of RAM wonder whether that is really needed... Aren't there more efficient representations for information exchange?

> 
> I don't think there's any way to pre-calculate it. The libqb library is
> the part of the software stack that actually manages the shared memory,
> but it's used by everything -- corosync (including its cpg and
> votequorum components) and each pacemaker daemon.
> 
> The size depends directly on the amount of communication activity in the
> cluster, which is only indirectly related to the number of
> nodes/resources/etc., the size of the CIB, etc. A cluster with nodes
> joining/leaving frequently and resources moving around a lot will use
> more shared memory than a cluster of the same size that's quiet. Cluster
> options such as cluster-recheck-interval would also matter.
> 
> Practically, I think all you can do is simulate expected cluster
> configurations and loads, and see what it comes out to be.
[...]


Regards,
Ulrich