I think Erick posted https://community.datastax.com/questions/6947/. explained very clearly.
We hit same issue only on a huge table when upgrade, and we changed back after done. My understanding, Which option to chose, shall depend on your user case. If chasing high performance on a big table, then go default one, and increase capacity in memory, nowadays hardware is cheaper. Thanks, Jim On Mon, Aug 2, 2021 at 7:12 PM Amandeep Srivastava < amandeep.srivastava1...@gmail.com> wrote: > Can anyone please help with the above questions? To summarise: > > 1) What is the impact of using mmap only for indices besides a degradation > in read performance? > 2) Why does the off heap consumed during Cassandra full repair remains > occupied 12+ hours after the repair completion and is there a > manual/configuration driven way to clear that earlier? > > Thanks, > Aman > > On Thu, 29 Jul, 2021, 6:47 pm Amandeep Srivastava, < > amandeep.srivastava1...@gmail.com> wrote: > >> Hi Erick, >> >> Limiting mmap to index only seems to have resolved the issue. The max ram >> usage remained at 60% this time. Could you please point me to the >> limitations for setting this param? - For starters, I can see read >> performance getting reduced up to 30% (CASSANDRA-8464 >> <https://issues.apache.org/jira/browse/CASSANDRA-8464>) >> >> Also if you could please shed light on extended questions in my earlier >> email. >> >> Thanks a lot. >> >> Regards, >> Aman >> >> On Thu, Jul 29, 2021 at 12:52 PM Amandeep Srivastava < >> amandeep.srivastava1...@gmail.com> wrote: >> >>> Thanks, Bowen, don't think that's an issue - but yes I can try upgrading >>> to 3.11.5 and limit the merkle tree size to bring down the memory >>> utilization. >>> >>> Thanks, Erick, let me try that. >>> >>> Can someone please share documentation relating to internal functioning >>> of full repairs - if there exists one? Wanted to understand the role of the >>> heap and off-heap memory separately during the process. >>> >>> Also, for my case, once the nodes reach the 95% memory usage, it stays >>> there for almost 10-12 hours after the repair is complete, before falling >>> back to 65%. Any pointers on what might be consuming off-heap for so long >>> and can something be done to clear it earlier? >>> >>> Thanks, >>> Aman >>> >>> >>> >> >> -- >> Regards, >> Aman >> >
