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From Esteban Gutierrez <este...@cloudera.com>
Subject Re: Changing it so we do NOT archive hfiles by default
Date Fri, 21 Nov 2014 23:16:06 GMT
For the specific case Stack mentioned here there are no snapshots enabled
and its an 0.94.x release so no real need for this user to have the archive
enabled. I've also seen this issue on 0.98 on with a busy NN (deletions
pile up)

I think it should be fine to fall back to the old behavior if snapshots are
not being used and delete compacted files or HFiles from a dropped table
immediately.

One problem with HBASE-11360 was to maintain a better compatibility with
snapshots in the current they work in branch-1 with the manifest file.

cheers,
esteban.




--
Cloudera, Inc.


On Fri, Nov 21, 2014 at 2:50 PM, Dave Latham <latham@davelink.net> wrote:

> Yes, there were definitely issues with the way the file cleaners worked
> where it ends up doing NameNode lookups or even scans for every single file
> before the cleaner allows it to be removed.
> What version of HBase are these folks using?  Do they have snapshots
> enabled?
> Here's tickets where we fixed a couple of these performance issues where
> the master just could not keep up at large scale:
> HBASE-9208 for slow ReplicationLogCleaner and HBASE-11360 for usage of the
> SnapshotFileCache.
> The fixes were generally to check batches of files at a time instead of
> hitting the NameNode for every file.
>
> I'm sorry to see that HBASE-11360 was reverted with HBASE-11742 so if
> snapshots are enabled that could be the same issue.
>
> I'd be sad to see the solution be that you can't both have snapshots or
> backups and operate at large scale.
>
> Dave
>
> On Thu, Nov 20, 2014 at 12:42 PM, Stack <stack@duboce.net> wrote:
>
> > On Thu, Nov 20, 2014 at 12:21 PM, lars hofhansl <larsh@apache.org>
> wrote:
> >
> > > Interesting that removing the files (which is just a metadata operation
> > in
> > > the NN) is slower than writing the files with all their data in the
> first
> > > place.Is it really the NN that is the gating factor or is it the
> > algorithm
> > > we have in HBase? I remember we had similar issue with the HLog removal
> > > where we rescan the WAL directory over and over for no good reason, and
> > the
> > > nice guys from Flurry did a fix.
> > >
> >
> > There is yes, an open question on why the cleaner can not keep up. Am
> > looking into this too (High level, millions of files in a single dir)
> >
> >
> >
> > > We have a lot of stuff relying on this now, so it should be done
> > > carefully. You thinking 1.0+, or even earlier releases?
> > >
> > >
> > Yes. It seems a bunch of items have come to rely on this behavior since
> it
> > was introduced way back. Was thinking 1.0, yes, but after the input  here
> > and offlist by Matteo, my hope of an easy fix has taken a dent.
> >
> > Thanks for the input lads,
> > St.Ack
> >
> >
> >
> >
> > > -- Lars
> > >       From: Stack <stack@duboce.net>
> > >  To: HBase Dev List <dev@hbase.apache.org>
> > >  Sent: Thursday, November 20, 2014 11:08 AM
> > >  Subject: Changing it so we do NOT archive hfiles by default
> > >
> > > I think we should swap the default that has us archive hfiles rather
> than
> > > just outright delete them when we are done with them. The current
> > > configuration works for the minority of us who are running backup
> tools.
> > > For the rest of us, our clusters are doing unnecessary extra work.
> > >
> > > Background:
> > >
> > > Since 0.94 (https://issues.apache.org/jira/browse/HBASE-5547), when we
> > are
> > > done with an hfile, it is moved to the 'archive' (hbase/.archive)
> > > directory. A thread in the master then removes hfiles older than some
> > > configured time. We do this rather than just delete hfiles to
> facilitate
> > > backup tools -- let backup tools have a say in when an hfile is safe to
> > > remove.
> > >
> > > The subject on HBASE-5547 has it that the archiving behavior only
> happens
> > > when the cluster is in 'backup mode', but as it turns out, later in the
> > > issue discussion, the implementation becomes significantly easier if we
> > > just always archive and that is what we ended up implementing and
> > > committing.
> > >
> > > These last few days, a few of us have been helping a user on a large
> > > cluster who is (temporarily) doing loads of compactions with the
> replaced
> > > hfiles being moved to hbase/.archive. The cleaning thread in master is
> > not
> > > working fast enough deleting the hfiles so there is buildup going on --
> > so
> > > much so, its slowing the whole cluster down (NN operations over tens of
> > > millions of files).
> > >
> > > Any problem swapping the default and having users opt-in for archiving?
> > > (I'd leave it as is in released software).  I will also take a look at
> > > having the cleaner thread do more work per cycle.
> > >
> > > Thanks,
> > > St.Ack
> > >
> > >
> > >
> > >
> >
>

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