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Subject: Re: collision in the naming of '.snapshot' directory between hdfs
 snapshot and hbase snapshot
From: Ted Yu <yuzhihong@gmail.com>
To: dev@hbase.apache.org
Cc: lars hofhansl <larsh@apache.org>,
	"hdfs-dev@hadoop.apache.org" <hdfs-dev@hadoop.apache.org>
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bq. let's make the hbase snapshot for a conf variable.

Once we decide on the new name of snapshot directory, we should still use
hardcoded value. This aligns with current code base:
See this snippet from HConstants:

  public static final List<String> HBASE_NON_TABLE_DIRS =

    Collections.unmodifiableList(Arrays.asList(new String[] {
HREGION_LOGDIR_NAME,

      HREGION_OLDLOGDIR_NAME, CORRUPT_DIR_NAME, SPLIT_LOGDIR_NAME,

      HBCK_SIDELINEDIR_NAME, HFILE_ARCHIVE_DIRECTORY, SNAPSHOT_DIR_NAME,
HBASE_TEMP_DIRECTORY }));
Cheers

On Mon, Apr 15, 2013 at 8:24 PM, Jonathan Hsieh <jon@cloudera.com> wrote:

> 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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