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https://issues.apache.org/jira/browse/HDFS-3120?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13241415#comment-13241415
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Tsz Wo (Nicholas), SZE commented on HDFS-3120:
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> Let's add a new dfs.support.hsync option ...
There is a little problem that sync in 1.x and hflush in 2.x are different.
They different methods and slightly different semantic. Do we really need this
new option? How about change dfs.support.append for only append. Sync/hflush
is always enabled.
> Provide ability to enable sync without append
> ---------------------------------------------
>
> Key: HDFS-3120
> URL: https://issues.apache.org/jira/browse/HDFS-3120
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 1.0.1
> Reporter: Eli Collins
> Assignee: Eli Collins
>
> 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.hsync* 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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