Missed the heap part, not sure why is that happening On Tue, Aug 3, 2021 at 8:59 AM manish khandelwal < manishkhandelwa...@gmail.com> wrote:
> mmap is used for faster reads and as you guessed right you might see read > performance degradation. If you are seeing high memory usage after repairs > due to mmaped files, the only way to reduce the memory usage is to trigger > some other process which requires memory. *mmapped* files use > buffer/cache memory which gets released as soon as some other process > requests memory from the kernel. Kernel does not want to waste its effort > until some request for resource comes in. > > > > On Tue, Aug 3, 2021 at 4:42 AM 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 >>> >>
