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From "Jay Patel (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7882) Allow disabling slab allocation for off-heap memtables
Date Fri, 05 Sep 2014 09:11:28 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7882?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14122706#comment-14122706
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Jay Patel commented on CASSANDRA-7882:
--------------------------------------

Is this overhead from using jemalloc allocator, or this happens with native gcc as well? BTW,
I've opened a related ticket CASSANDRA-7883 to allow plugging jemalloc. And, CASSANDRA-7884
to make the region size configurable. 

I think logarithmically scaling from 1K to 1 MB option can also work. But, should we keep
the start & end region-size configurable? Usually, this will be advanced option to tune
but very helpful. By default, we can keep 1 MB region size as most use cases will not need
to pack many tables. 

Let me know the best way to handle this, and also you can assign it to me to have it in 2.1.1.
We're actually quite dependent on this as currently 1 MB is putting a upper limit on number
of tables in the cluster & having multiple under-utilized clusters to support high # of
tables is not cost-effective.


> Allow disabling slab allocation for off-heap memtables
> ------------------------------------------------------
>
>                 Key: CASSANDRA-7882
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7882
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jay Patel
>             Fix For: 2.1.1
>
>
> CASSANDRA-5935 allows option to disable region-based allocation for on-heap memtables
but there is no option to disable it for off-heap memtables (memtable_allocation_type: offheap_objects).

> Disabling region-based allocation will allow us to pack more tables in the schema since
minimum of 1MB region won't be allocated per table. Downside can be more fragmentation which
should be controllable by using better allocator like JEMalloc.
> How about below option in yaml?:
> memtable_allocation_type: unslabbed_offheap_objects
> Thanks.



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