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From "Anoop Sam John (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HBASE-12295) Prevent block eviction under us if reads are in progress from the BBs
Date Fri, 29 May 2015 12:17:18 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14564689#comment-14564689
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Anoop Sam John edited comment on HBASE-12295 at 5/29/15 12:16 PM:
------------------------------------------------------------------

In CP case also, then we have expectation from user to explicitely call close().  We are copying
cell considering the fact that it might get stored and used later (by CP). Those kind of use
cases (HIndex for eg) might not be always the case.  So we can say if the CP has such a case
then they have to be aware of this SharedMemoryCell and do copy on their own? Just throwing
thoughts coming.

For non java case, any way we will need a copy. Right now using HBaseZeroCopyByteString we
avoid the copy need to make a PBCell from Cell. But all types of ByteString from PB need a
byte[] as backing data structure. When the cells are backed by DBB, we have to copy here.
 So there is not much adv we get. I would say in such a scenario copy the cell at one shot
in Region level is better. 


was (Author: anoop.hbase):
In CP case also, then we have expectation from user to explicitely call close().  We are copying
cell considering the fact that it might get stored and used later (by CP). Those kind of use
cases (HIndex for eg:) might not be always the case.  So we can say if the CP has such a case
then they have to be aware of this SharedMemoryCell and do copy on their own? Just throwing
thoughts coming.

For non java case, any way we will need a copy. Right now using HBaseZeroCopyByteString we
avoid the copy need to make a PBCell from Cell. But all types of ByteString from PB need a
byte[] as backing data structure. When the cells are backed by DBB, we have to copy here.
 So there is not much adv we get. I would say in such a scenario copy the cell at one shot
in Region level is better. 

> 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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