Thanks for the responses. Appreciae it. @Dor, so you are saying if we add "memlock unlimited" in limits.conf, the entire heap (Xms=Xmx) can be locked at startup ? Will this be applied to all Java processes ? We have couple of Java programs running with the same owner.
Thanks Kunal On Thu, Apr 16, 2020 at 4:31 PM Dor Laor <d...@scylladb.com> wrote: > It is good to configure swap for the OS but exempt Cassandra > from swapping. Why is it good? Since you never know the > memory utilization of additional agents and processes you or > other admins will run on your server. > > So do configure a swap partition. > You can control the eagerness of the kernel by the swappiness > sysctl parameter. You can even control it per cgroup: > > https://askubuntu.com/questions/967588/how-can-i-prevent-certain-process-from-being-swapped > > You should make sure Cassandra locks its memory so the kernel > won't choose its memory to be swapped out (since it will kill > your latency). You do it by mlock. Read more on: > > https://stackoverflow.com/questions/578137/can-i-tell-linux-not-to-swap-out-a-particular-processes-memory > > The scylla /dist/common/limits.d/scylladb.com looks like this: > scylla - core unlimited > scylla - memlock unlimited > scylla - nofile 200000 > scylla - as unlimited > scylla - nproc 8096 > > On Thu, Apr 16, 2020 at 3:57 PM Nitan Kainth <nitankai...@gmail.com> > wrote: > > > > Swap is controlled by OS and will use it when running short of memory. I > don’t think you can disable at Cassandra level > > > > > > Regards, > > > > Nitan > > > > Cell: 510 449 9629 > > > > > > On Apr 16, 2020, at 5:50 PM, Kunal <kunal.v...@gmail.com> wrote: > > > > > > > > Hello, > > > > > > > > I need some suggestion from you all. I am new to Cassandra and was > reading Cassandra best practices. On one document, it was mentioned that > Cassandra should not be using swap, it degrades the performance. > > > > My question is instead of disabling swap system wide, can we force > Cassandra not to use swap? Some documentation suggests to use > memory_locking_policy in cassandra.yaml. > > > > > > How do I check if our Cassandra already has this parameter and still > uses swap ? Is there any way i can check this. I already checked > cassandra.yaml and dont see this parameter. Is there any other place i can > check and confirm? > > > > > > Also, Can I set memlock parameter to unlimited (64kB default), so entire > Heap (Xms = Xmx) can be locked at node startup ? Will that help? > > > > > > Or if you have any other suggestions, please let me know. > > > > > > > > > > > > Regards, > > > > Kunal > > > > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: user-unsubscr...@cassandra.apache.org > For additional commands, e-mail: user-h...@cassandra.apache.org > > -- Regards, Kunal Vaid
