[ClusterLabs] Syncing data and reducing CPU utilization of cib process

[Nikhil Utane]

Ken,

The CIB file is not being updated that often.
I took a packet capture and don't see the node sending any message to other
nodes (other than keep-alives).
What then explains these messages coming every second?

-Regards
Nikhil

On Sat, Apr 1, 2017 at 1:37 AM, Ken Gaillot <kgaillot at redhat.com> wrote:

> On 03/31/2017 06:44 AM, Nikhil Utane wrote:
> > We are seeing this log in pacemaker.log continuously.
> >
> > Mar 31 17:13:01 [6372] 0005B932ED72        cib:     info:
> > crm_compress_string:  Compressed 436756 bytes into 14635 (ratio 29:1) in
> > 284ms
> >
> > This looks to be the reason for high CPU. What does this log indicate?
>
> If a cluster message is larger than 128KB, pacemaker will compress it
> (using BZ2) before transmitting it across the network to the other
> nodes. This can hit the CPU significantly. Having a large resource
> definition makes such messages more common.
>
> There are many ways to sync a configuration file between nodes. If the
> configuration rarely changes, a simple rsync cron could do it.
> Specialized tools like lsyncd are more responsive while still having a
> minimal footprint. DRBD or shared storage would be more powerful and
> real-time. If it's a custom app, you could even modify it to use
> something like etcd or a NoSQL db.
>
> >
> > -Regards
> > Nikhil
> >
> >
> > On Fri, Mar 31, 2017 at 12:08 PM, Nikhil Utane
> > <nikhil.subscribed at gmail.com <mailto:nikhil.subscribed at gmail.com>>
> wrote:
> >
> >     Hi,
> >
> >     In our current design (which we plan to improve upon) we are using
> >     the CIB file to synchronize information across active and standby
> nodes.
> >     Basically we want the standby node to take the configuration that
> >     was used by the active node so we are adding those as resource
> >     attributes. This ensures that when the standby node takes over, it
> >     can read all the configuration which will be passed to it as
> >     environment variables.
> >     Initially we thought the list of configuration parameters will be
> >     less and we did some prototyping and saw that there wasn't much of
> >     an issue. But now the list has grown it has become close to 300
> >     attributes. (I know this is like abusing the feature and we are
> >     looking towards doing it the right way).
> >
> >     So I have two questions:
> >     1) What is the best way to synchronize such kind of information
> >     across nodes in the cluster? DRBD? Anything else that is simpler?
> >     For e.g. instead of syncing 300 attributes i could just sync up the
> >     path to a file.
> >
> >     2) In the current design, is there anything that I can do to reduce
> >     the CPU utilization of cib process? Currently it regularly takes
> >     30-50% of the CPU.
> >     Any quick fix that I can do which will bring it down? For e.g.
> >     configure how often it synchronizes etc?
> >
> >     -Thanks
> >     Nikhil
>
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