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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 Thu, 27 Aug 2015 15:51:46 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9738?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14716905#comment-14716905
] 

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

How big is the realistic size range of key cache values?

The only thing that makes me uncomfortable right now is the buffer handling for the serializing
the key cache value in serializedSize(). Resizing in the loop is 4k at a time and not doubling.
I think it at least needs to double to manage whatever the worst case is.

It seems to me like the right tack on failure is to allocate the correct size buffer by calculating
the size the old way or double (for lg(n)). Doubling is fine if we really never expect sane
data models to hit it. Doubling is not going to be great for people to hit under real world
conditions especially if they have to do it several times.

It's tempting to ask to have 10189 expanded to be "make this stuff fast" and then do it the
old way in this change set, but I could be convinced if there isn't a really bad corner case.

Also next time could you wait +1 to squash? I can't see your last few change sets once you
squash. I am guilty of this too and now I know how it feels.

> 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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