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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5074) support checksums in HBase block cache
Date Tue, 20 Dec 2011 07:23:32 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5074?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13172994#comment-13172994
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Todd Lipcon commented on HBASE-5074:
------------------------------------

bq. Once the block is read into the hbase cache, it will verify the checksum and if not valid,
have to use a new HDFS api to read in contents from another hdfs replica

Rather than adding a new API to read from another replica, HBase could instead just trigger
a second pread from HDFS _with_ the verifyChecksum flag set. This would cause HDFS to notice
the checksum error based on its own checksums, and do the "right thing" (ie report the bad
replica, fix it up, etc).
                
> support checksums in HBase block cache
> --------------------------------------
>
>                 Key: HBASE-5074
>                 URL: https://issues.apache.org/jira/browse/HBASE-5074
>             Project: HBase
>          Issue Type: Improvement
>          Components: regionserver
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>
> The current implementation of HDFS stores the data in one block file and the metadata(checksum)
in another block file. This means that every read into the HBase block cache actually consumes
two disk iops, one to the datafile and one to the checksum file. This is a major problem for
scaling HBase, because HBase is usually bottlenecked on the number of random disk iops that
the storage-hardware offers.

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