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From Ted Yu <yuzhih...@gmail.com>
Subject Re: collision in the naming of '.snapshot' directory between hdfs snapshot and hbase snapshot
Date Tue, 16 Apr 2013 17:00:10 GMT
Let's get proper release notes for HBASE-8352 .

Either Lars or I can send out notification to user mailing list so that
there is enough preparation for this change.

Cheers

On Tue, Apr 16, 2013 at 8:46 AM, Jonathan Hsieh <jon@cloudera.com> wrote:

> I was away from keyboard when I asserted that hdfs snapshot was a hadoop
> 2.1 or 3.0 feature.  Apparently it is targeted as a hadoop 2.0.5 feature.
>  (I'm a little surprised -- expected this to be a hadoop2 compat breaking
> feature) -- so I agree that this is a bit more urgent.
>
> Anyway, I agree that the fs .snapshot naming convention is long standing
> and should win.
>
> My concern is with breaking compatibility in 0.94 again -- if we don't go
> down the conf variable route,  I consider having docs to properly document
> how to do the upgrade and caveats of doing the upgrade in the docs/release
> notes blocker to hbase 0.94.7.  (specifically mentioning from 0.94.6 to
> 0.94.7, and to possibly to 0.95).
>
> Jon.
>
> On Mon, Apr 15, 2013 at 9:00 PM, Ted Yu <yuzhihong@gmail.com> wrote:
>
> > bq. Alternatively, we can detect the underlying Hadoop version, and use
> > either .snapshot or .hbase_snapshot in 0.94 depending on h1 & h2.
> >
> > I think this would introduce more confusion, especially for operations.
> >
> > Cheers
> >
> > On Mon, Apr 15, 2013 at 8:52 PM, Enis Söztutar <enis.soz@gmail.com>
> wrote:
> >
> > > 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
> > > > >
> > > >
> > >
> >
>
>
>
> --
> // Jonathan Hsieh (shay)
> // Software Engineer, Cloudera
> // jon@cloudera.com
>

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