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From Enis Söztutar <enis....@gmail.com>
Subject Re: collision in the naming of '.snapshot' directory between hdfs snapshot and hbase snapshot
Date Tue, 16 Apr 2013 03:52:11 GMT
Because HDFS exposes the snapshots so that the normal file system
operations are mapped inside snapshot dirs, I think HDFS reserving the
.snapshot name makes sense. OTOH, nothing is specific about the dir name
that is chosen by HBase.

I would prefer to change the dir name in 0.94 as well, since 0.94 is also
being run on top of hadoop 2. Alternatively, we can detect the underlying
Hadoop version, and use either .snapshot or .hbase_snapshot in 0.94
depending on h1 & h2.

Enis


On Mon, Apr 15, 2013 at 8:31 PM, Ted Yu <yuzhihong@gmail.com> wrote:

> 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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