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From Stack <st...@duboce.net>
Subject Re: Changing it so we do NOT archive hfiles by default
Date Thu, 20 Nov 2014 20:42:39 GMT
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,

> -- 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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