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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3120) Enable hsync and hflush by default
Date Mon, 02 Apr 2012 22:37:23 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3120?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13244766#comment-13244766
] 

Todd Lipcon commented on HDFS-3120:
-----------------------------------

Patch looks OK. Can you verify TestFileAppend4 locally before committing? Seems suspect that
an append-related test would fail with this append-related patch.
                
> Enable hsync and hflush by default
> ----------------------------------
>
>                 Key: HDFS-3120
>                 URL: https://issues.apache.org/jira/browse/HDFS-3120
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Eli Collins
>            Assignee: Eli Collins
>         Attachments: hdfs-3120.txt
>
>
> The work on branch-20-append was to support *sync*, for durable HBase WALs, not *append*.
The branch-20-append implementation is known to be buggy. There's been confusion about this,
we often answer queries on the list [like this|http://search-hadoop.com/m/wfed01VOIJ5]. Unfortunately,
the way to enable correct sync on branch-1 for HBase is to set dfs.support.append to true
in your config, which has the side effect of enabling append (which we don't want to do).
> Let's add a new *dfs.support.sync* option that enables working sync (which is basically
the current dfs.support.append flag modulo one place where it's not referring to sync). For
compatibility, if dfs.support.append is set, dfs.support.sync will be set as well. This way
someone can enable sync for HBase and still keep the current behavior that if dfs.support.append
is not set then an append operation will result in an IOE indicating append is not supported.
We should do this on trunk as well, as there's no reason to conflate hsync and append with
a single config even if append works.

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