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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12295) Prevent block eviction under us if reads are in progress from the BBs
Date Mon, 01 Jun 2015 22:48:18 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14568176#comment-14568176

stack commented on HBASE-12295:

bq. ...Regarding knowing whether L1 or L2 looking at key...

Do what makes sense. If keeping type in HFileBlock makes more sense, then ok, no problem passing
block on close/when done.

bq. We have to see what else we can do to return this payload.

Yeah, not sure how to encapsulate blockcache blocks while making it so we can delay the copy
to cellblock long as possible... as far out as possible in the read path.

bq. I think I got now what is in your mind on saying finalize/close on Result and handle things
that way. ...I would say this will add more complexity and chances we miss the close. What
do you think?

Not sure I follow the objection, but ok if you think it might make things more complex. Lets
see how we figure getting from blockcache block to cellblock....

bq. Ref counts purely happens in the L2_CACHE layer alone and the ref count is associated
with the bucket entry. None of the above layers know about it....

That is good. Ignore my suggestions that would go against the above.

bq. if Result needs to do the 'finally' may be it should be exposed to some more internals
of the scans and the scanners?...

Yeah, serverside Result would have to know more about internals.... so could do release. Seems
like Get needs to NOT return Result on serverside ... should be like scan.

> Prevent block eviction under us if reads are in progress from the BBs
> ---------------------------------------------------------------------
>                 Key: HBASE-12295
>                 URL: https://issues.apache.org/jira/browse/HBASE-12295
>             Project: HBase
>          Issue Type: Sub-task
>          Components: regionserver, Scanners
>            Reporter: ramkrishna.s.vasudevan
>            Assignee: ramkrishna.s.vasudevan
>             Fix For: 2.0.0
>         Attachments: HBASE-12295.pdf, HBASE-12295_trunk.patch
> While we try to serve the reads from the BBs directly from the block cache, we need to
ensure that the blocks does not get evicted under us while reading.  This JIRA is to discuss
and implement a strategy for the same.

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