Impact analysis of upgrading RHEL/SLES OS

[Pushpendra Rajpoot <pu...@gmail.com>]

Hi All,

I am running Cassandra 3.11.2 on RHEL 7.4. I am planning for an OS upgrade
from RHEL 7.4 to RHEL 7.9/8.x and SLES15. But I could not find any relevant
information on the impact of upgrading an OS.

Could you share any reference or your analysis of these impacts? I would
appreciate it if you could share your thoughts.

Regards,
Pushpendra

Re: Impact analysis of upgrading RHEL/SLES OS

[Erick Ramirez <er...@datastax.com>]

In most cases, minor OS upgrades are not problematic provided you have
sufficient capacity in your cluster so that it can tolerate scheduled
downtime while some nodes are being upgraded.

One thing you should be aware of are patches in newer versions of Linux
distributions which address Spectre and Meltdown vulnerabilities. The
microcode and security patches in RHEL 7.7 can have a significant impact on
the performance of servers. Note that this is not limited to Cassandra
workloads -- the fixes are applied at the OSI layer so it affects all
applications and databases running on patched operating systems. You can
find out more information about the RHEL patches in this KB --
https://access.redhat.com/articles/3311301.

Some recommended mitigation strategies for the performance impacts include:

   - Reviewing disk configuration, particularly setting a low(er)
   read-ahead size. See this blog post from The Last Pickle for guidance --
   https://thelastpickle.com/blog/2019/01/30/new-cluster-recommendations.html
   .
   - Disabling governors which use a lower CPU frequency, or explicitly
   setting CPU scaling to "performance". For reference, I previously wrote
   about this here --
   https://support.datastax.com/hc/en-us/articles/115003018063.
   - Set the disk access mode to mmap index files only. I've explained the
   details in this post -- https://community.datastax.com/questions/6947/.

Cheers!

Re: Impact analysis of upgrading RHEL/SLES OS

[Kane Wilson <k...@raft.so>]

OS upgrades most often don't have any impact on C*, and you'd likely only
expect trouble on a major upgrade, but this would typically be related to
package installation, rather than any effects on the database itself.
I wouldn't be too worried about going from RHEL7.4 to 7.9, however going to
8 you may want to test your installation/systemd units/OS settings you may
have tuned.
Best practice is to do a test run on a non production cluster, and always
perform a rolling upgrade one node at a time to ensure no downtime.

Also play it safe and don't perform more than one operation at a time. Do
the OS upgrade only - and try to avoid changes to Cassandra itself.

Cheers,
Kane

raft.so - Cassandra consulting, support, and managed services


On Mon, Mar 1, 2021 at 2:30 PM Pushpendra Rajpoot <
pushpendra.nh.rajpoot@gmail.com> wrote:

> Hi All,
>
> I am running Cassandra 3.11.2 on RHEL 7.4. I am planning for an OS
> upgrade from RHEL 7.4 to RHEL 7.9/8.x and SLES15. But I could not find any
> relevant information on the impact of upgrading an OS.
>
> Could you share any reference or your analysis of these impacts? I would
> appreciate it if you could share your thoughts.
>
> Regards,
> Pushpendra
>