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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6868) Skip checksum is broke; are we double-checksumming by default?
Date Sun, 23 Sep 2012 00:19:07 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6868?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13461299#comment-13461299
] 

Lars Hofhansl commented on HBASE-6868:
--------------------------------------

@Jerry: That seems like a better approach. It always bothers me when we're trying to solve
HDFS problems in HBase. On the other hand that change will never (at or at least much later)
be in an official HDFS.

@binlijin:
Are you sure about case (2)? You're saying that even if dfs.client.read.shortcircuit.skip.checksum=false
the DFSClient will still skip the checksumming?

Are there more cases:
(3a) the block is not local.
Both DFSClient and HRegionserver will calculate the checksum
(4) dfs.client.read.shortcircuit = false, dfs.client.read.shortcircuit.skip.checksum=true
Both DFSClient and HRegionserver will calculate the checksum

?

I it seems we're mostly good here. The double checksumming for non local blocks is not ideal
of course (but that's HDFS-3429)
                
> Skip checksum is broke; are we double-checksumming by default?
> --------------------------------------------------------------
>
>                 Key: HBASE-6868
>                 URL: https://issues.apache.org/jira/browse/HBASE-6868
>             Project: HBase
>          Issue Type: Bug
>          Components: HFile, wal
>    Affects Versions: 0.94.0, 0.94.1
>            Reporter: LiuLei
>            Priority: Blocker
>             Fix For: 0.94.3, 0.96.0
>
>
> The HFile contains checksums for decrease the iops, so when Hbase read HFile , that dont't
need to read the checksum from meta file of HDFS.  But HLog file of Hbase don't contain the
checksum, so when HBase read the HLog, that must read checksum from meta file of HDFS.  We
could  add setSkipChecksum per file to hdfs or we could write checksums into WAL if this skip
checksum facility is enabled 

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