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Date: Mon, 15 Apr 2013 20:24:12 -0700
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Subject: collision in the naming of '.snapshot' directory between hdfs
 snapshot and hbase snapshot
From: Jonathan Hsieh <jon@cloudera.com>
To: "dev@hbase.apache.org" <dev@hbase.apache.org>,
 lars hofhansl <larsh@apache.org>
Cc: "hdfs-dev@hadoop.apache.org" <hdfs-dev@hadoop.apache.org>
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constraints:

1) hbase 0.94.6 is released and .snapshot is hardcoded in there.
2) hdfs snapshots is a Hadoop 2.1 or 3.0 feature. I doubt that it will ever
make it to 1.x.  This hdfs feature ideally this shouldn't affect current A
pache Hbase 0.94.x's.
3) hbase 95/96 may default to Hadoop1 or Hadoop 2. these versions should
pick a different table snapshot name to respect fs conventions.

proposed actions:

1) let's make the hbase snapshot for a conf variable. (hbase.
snapshots.dir)  let's change the default for hbase 95+. (maybe
.hbase-snapshots). we'll also port this patch to 0.94.x
2) let's publish instructions on how to update the hbase snapshot dir:
shutdown hbase, config update, rename dir, restart hbase.
3) I lean towards leaving the current default hbase snapshot dir in 94
since it shouldn't be affected.  upgrading hbase to 95/96 will require
shutdown and update scripts so it seems like the ideal time to autoforce
this default change.

Thoughts?


On Monday, April 15, 2013, lars hofhansl wrote:

> OK. Let's try to fix that quickly, so that I can release HBase 0.94.7.
>
> -- Lars
>
>
>
> ________________________________
>  From: Ted Yu <yuzhihong@gmail.com>
> To: dev@hbase.apache.org; hdfs-dev@hadoop.apache.org
> Sent: Monday, April 15, 2013 7:13 PM
> Subject: collision in the naming of '.snapshot' directory between hdfs
> snapshot and hbase snapshot
>
>
> Hi,
> This afternoon Huned ad I discovered an issue while playing with HBase
> Snapshots on top of Hadoop's Snapshot branch (
> http://svn.apache.org/viewvc/hadoop/common/branches/HDFS-2802/).
>
> HDFS (built from HDFS-2802 branch) doesn't allow paths with .snapshot as a
> component while HBase tries to create paths with .snapshot as a component.
> This leads to issues in HBase, and one of HDFS or HBase needs to give up
> the .snapshot reserved keyword. HBase released Snapshots feature in 0.94.6
> (quite recently) and it may not be too late to change HBase to use a
> different path component in an upcoming new release.
>
> In HBase these path names are not user visible. If there is a deployment of
> 0.94.6, one could provide a migration tool that renames .snapshot to
> .hbase-snapshot or something to be able to move to the Snapshot release of
> Hadoop. On the other hand, .snapshot in HDFS is a user visible name and is
> a convention that is used by many file systems. It's a matter of
> familiarity with such path names that would help users in using HDFS
> snapshots.
>
> I am including the hdfs-dev in this email. Would appreciate if we could
> work together and come up with a solution.
>
> You can find sample output from hdfs command here:
> http://pastebin.com/bBqR4Fvr
>
> Cheers


-- 
// Jonathan Hsieh (shay)
// Software Engineer, Cloudera
// jon@cloudera.com

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