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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 Thu, 01 Aug 2013 17:25:49 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9102?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13726635#comment-13726635
] 

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

Chao, You are right that the pre-load will run in a rate/limit fashion to make sure it won't
pollute the block cache substantially.
The pre-loading targets on the large sequential scan case. The client is able to enable/disable
on each request basis. 

                
> 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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