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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6490) 'dfs.client.block.write.retries' value could be increased in HBase
Date Tue, 21 Aug 2012 16:58:37 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6490?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13438854#comment-13438854
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stack commented on HBASE-6490:
------------------------------

What should we increase it to N?  We can't increase it just for WAL... it'd be globally?
                
> 'dfs.client.block.write.retries' value could be increased in HBase
> ------------------------------------------------------------------
>
>                 Key: HBASE-6490
>                 URL: https://issues.apache.org/jira/browse/HBASE-6490
>             Project: HBase
>          Issue Type: Improvement
>          Components: master, regionserver
>    Affects Versions: 0.96.0
>         Environment: all
>            Reporter: nkeywal
>            Priority: Minor
>
> When allocating a new node during writing, hdfs tries 'dfs.client.block.write.retries'
times (default 3) to write the block. When it fails, it goes back to the nanenode for a new
list, and raises an error if the number of retries is reached. In HBase, if the error is while
we're writing a hlog file, it will trigger a region server abort (as hbase does not trust
the log anymore). For simple case (new, and as such empty log file), this seems to be ok,
and we don't lose data. There could be some complex cases if the error occurs on a hlog file
with already multiple blocks written.
> Logs lines are:
> "Exception in createBlockOutputStream", then "Abandoning block " followed by "Excluding
datanode " for a retry.
> IOException: "Unable to create new block.", when the number of retries is reached.
> Probability of occurence seems quite low, (number of bad nodes / number of nodes)^(number
of retries), and it implies that you have a region server without its datanode. But it's per
new block.
> Increasing the default value of 'dfs.client.block.write.retries' could make sense to
be better covered in chaotic conditions.

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