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Posted to user@cassandra.apache.org by "ZAIDI, ASAD A" <az...@att.com> on 2017/08/11 19:05:44 UTC

MemtablePostFlush pending

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

Re: MemtablePostFlush pending

Posted by Akhil Mehra <ak...@gmail.com>.

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 <az...@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

Re: MemtablePostFlush pending

Posted by Erick Ramirez <fl...@gmail.com>.

Check what you have set for memtable_cleanup_threshold and if it's set too
low which means more flushing triggered. Cheers!

On Sat, Aug 12, 2017 at 5:05 AM, ZAIDI, ASAD A <az...@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
>
>
>