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https://issues.apache.org/jira/browse/HDFS-3120?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13241903#comment-13241903
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Eli Collins commented on HDFS-3120:
-----------------------------------
Latest proposal:
For 1.x:
- Always enable the sync path (currently only enabled if dfs.support.append is
set)
- Remove the dfs.support.append configuration option. Let's keep the code paths
though in case we ever fix append on branch-1, in which case we can add the
config option back
For 2.x:
- Always enable the hsync/hflush path
- The dfs.support.appends only enables the append specific paths (since the
hsync/hflush paths are now always on). Append will still default to being
enabled so there is no net effect by default
Sound good?
> 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.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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