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From "Liyin Tang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9102) HFile block pre-loading for large sequential scan
Date Wed, 31 Jul 2013 18:05:50 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9102?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13725515#comment-13725515
] 

Liyin Tang commented on HBASE-9102:
-----------------------------------

It is true that OS cached the compressed/encoded blocks and the DFSClient non-pread operation
is also able to pre-load all the bytes up to that DFS block. And this feature is to pre-load
(decompress/decoded) these data blocks in additional to the OS cache/disk read-ahead.

Also the scan prefetch is currently implemented in the RegionScanner level. I think it is
a good idea to implement some prefetch logic in the HBase client as well.
                
> HFile block pre-loading for large sequential scan
> -------------------------------------------------
>
>                 Key: HBASE-9102
>                 URL: https://issues.apache.org/jira/browse/HBASE-9102
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 0.89-fb
>            Reporter: Liyin Tang
>            Assignee: Liyin Tang
>
> The current HBase scan model cannot take full advantage of the aggrediate disk throughput,
especially for the large sequential scan cases. And for the large sequential scan, it is easy
to predict what the next block to read in advance so that it can pre-load and decompress/decoded
these data blocks from HDFS into block cache right before the current read point. 
> Therefore, this jira is to optimized the large sequential scan performance by pre-loading
the HFile blocks into the block cache in a stream fashion so that the scan query can read
from the cache directly.

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