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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 09:54:25 GMT

    [ https://issues.apache.org/jira/browse/HBASE-15477?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15206081#comment-15206081
] 

Anoop Sam John commented on HBASE-15477:
----------------------------------------

{code}
if (hFileBlock.hasNextBlockHeader()) {		
181	            hFileBlock.buf.limit(hFileBlock.buf.limit() - hFileBlock.headerSize());		
182	          }
{code}
So this is removed now as we dont write next block's header with cur block..  So where is
this change of avoiding it?  When write in BC?

Also when this block is created out of a BB read from HDFS, that BB will contain the next
block's header also at the end.  So we dont need this limiting thing at all?  How on those
block's buffers we do the limit. (Some other place)  Because when reading cells, we will read
until block's buf.hasRemaining()

> 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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