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 <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 <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 <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 <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
