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From "Anoop Sam John (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-15477) Do not save 'next block header' when we cache hfileblocks
Date Tue, 22 Mar 2016 06:42:25 GMT

    [ https://issues.apache.org/jira/browse/HBASE-15477?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15205891#comment-15205891
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Anoop Sam John commented on HBASE-15477:
----------------------------------------

Got it Stack..  I found it confusing with the RB comments.. So instead of keeping all the
header bytes of the next block, we just keep its length ( so an extra 4 bytes). Make sense.
Let me read the full patch then

> Do not save 'next block header' when we cache hfileblocks
> ---------------------------------------------------------
>
>                 Key: HBASE-15477
>                 URL: https://issues.apache.org/jira/browse/HBASE-15477
>             Project: HBase
>          Issue Type: Sub-task
>          Components: BlockCache, Performance
>            Reporter: stack
>            Assignee: stack
>         Attachments: 15366v4.patch, 15477.patch, 15477v2.patch, 15477v3.patch, 15477v3.patch,
15477v4.patch
>
>
>     When we read from HDFS, we overread to pick up the next blocks header.
>     Doing this saves a seek as we move through the hfile; we save having to
>     do an explicit seek just to read the block header every time we need to
>     read the body.  We used to read in the next header as part of the
>     current blocks buffer. This buffer was then what got persisted to
>     blockcache; so we were over-persisting wrtiting out our block plus the
>     next blocks' header (overpersisting 33 bytes). Parse of HFileBlock
>     complicated by this extra tail. Fix.



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