We have been experiencing swap issues on rhel 8.7.4 across 1000s of nodes. https://access.redhat.com/solutions/6785021. This is obtrusive enough that our linux engineering team decided to push a patch through to all of our teams. Once we updated the appropriate setting per the link I shared, all swap issues went away.
On Thu, Jul 27, 2023 at 5:33 AM manish khandelwal < manishkhandelwa...@gmail.com> wrote: > Thanks Tibor. I know that swapping should be disabled, that is a general > recommendation. > I wanted to know i*f anyone using Cassandra on RHEL faced any issue while > moving from Rhel 7.x to Rhel 8.x. * > > Regards > Manish > > On Thu, Jul 27, 2023 at 2:29 PM Tibor Répási <tibor.rep...@anzix.org> > wrote: > >> That doesn’t sound like a RHEL issue. Swapping can severely impact >> performance, that’s why it is recommended to turn off swap on Cassandra >> nodes. This was recommended in the Cassandra documentation by DataStax[1]. >> Apache Cassandra is testing that and log a warning on startup [2] if >> swap is found enabled. >> >> Alternatively, the kernel behaviour can be tuned by setting the IO cost >> of swapping [3] that best fit your use-case. For a Cassandra node having >> sufficient physical memory this might end up at zero swappiness to prevent >> swapping at all [4]. >> >> [1] >> https://docs.datastax.com/en/cassandra-oss/3.x/cassandra/install/installRecommendSettings.html#Disableswap >> [2] >> https://github.com/apache/cassandra/blob/738dfde73560d289218f3afa4103a37e9f401757/src/java/org/apache/cassandra/utils/SigarLibrary.java#L172 >> [3] >> https://docs.kernel.org/admin-guide/sysctl/vm.html?highlight=swappiness#swappiness >> >> [4] >> https://www.ibm.com/docs/en/linux-on-systems?topic=settings-setting-swappiness-parameter-zero >> >> >> On 27. Jul 2023, at 10:14, manish khandelwal < >> manishkhandelwa...@gmail.com> wrote: >> >> Has anybody seen issues running Cassandra on RHEL 8.6. I am seeing >> performance dip while running Cassandra on RHEL8.6. Also with RHEL I am >> seeing swapping happening in spite of a lot of free memory available. In >> RHEL 7.9 we did not see any swapping with same workload and same RPM of >> Cassandra. Anyone running Cassandra on RHEL? >> >> Regards >> Manish >> >> >>
