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From "Ariel Weisberg (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9738) Migrate key-cache to be fully off-heap
Date Mon, 31 Aug 2015 19:36:49 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9738?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14723917#comment-14723917
] 

Ariel Weisberg commented on CASSANDRA-9738:
-------------------------------------------

I agree there is overlap in. The scope of what we need to make the key cache work is smaller,
but it might be game over for the key cache and large partitions anyways even with Robert's
improvements. Constantly loading and unloading large partitions is never going to work. We
are at least reaching parity with the old key cache.

If we could map the entire partition index then you could point this code at the mapping and
it would work. It would not be ideal because what we are doing is a basic translation of the
object graph which is an array pointing to variable size objects. Binary searches are going
to result in access to two pages for each comparison. Possibly still better than what we have
today?

I think the trick right now is figuring out what we can do for 3.0, and what the next intermediate
step is. If Robert goes and makes this work off-heap then the key cache can maybe go off heap
for 3.0. Seems like removing the key cache and reliably operating against a memory map is
unlikely for 3.0, but maybe shortly after.

What would the timeline be for 9754? That kind of determines what intermediate steps make
sense.

> Migrate key-cache to be fully off-heap
> --------------------------------------
>
>                 Key: CASSANDRA-9738
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9738
>             Project: Cassandra
>          Issue Type: Sub-task
>            Reporter: Robert Stupp
>            Assignee: Robert Stupp
>             Fix For: 3.0 beta 2
>
>
> Key cache still uses a concurrent map on-heap. This could go to off-heap and feels doable
now after CASSANDRA-8099.
> Evaluation should be done in advance based on a POC to prove that pure off-heap counter
cache buys a performance and/or gc-pressure improvement.
> In theory, elimination of on-heap management of the map should buy us some benefit.



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