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From Akhil Mehra <akhilme...@gmail.com>
Subject Re: MemtablePostFlush pending
Date Sun, 13 Aug 2017 22:19:51 GMT
HI Asad,

The post flush task frees up allocated commit log segments.

Apart for commit log segment allocation the post flush task "synchronises custom secondary
indexes and provides ordering guarantees for futures on switchMemtable/flush
etc, which expect to be able to wait until the flush (and all prior flushes) requested have
completed."

The post flush executor is a single threaded thread pool that cannot be tuned (https://github.com/apache/cassandra/blob/8b3a60b9a7dbefeecc06bace617279612ec7092d/src/java/org/apache/cassandra/db/ColumnFamilyStore.java#L160-L167
<https://github.com/apache/cassandra/blob/8b3a60b9a7dbefeecc06bace617279612ec7092d/src/java/org/apache/cassandra/db/ColumnFamilyStore.java#L160-L167>)

Are you using secondary indexes? I there a high write throughput which is resulting in frequent
meltable flushes?

Regards,
Akhil





> On 12/08/2017, at 7:05 AM, ZAIDI, ASAD A <az192g@att.com> wrote:
> 
> Hello Folks,
>  
> I’m using Cassandra 2.2 on 14 node cluster.
>  
> Now a days, I’m observing memtablepostflush pending number going high , this happens
intermittently. I’m looking if  Is there way to ‘tune’ memtablepostflush stage?
>  
> Thanks/ASad


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