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From Matteo Bertozzi <theo.berto...@gmail.com>
Subject Re: Online snapshots are very slow?
Date Tue, 03 Mar 2015 17:53:42 GMT
On Tue, Mar 3, 2015 at 5:37 PM, Vladimir Rodionov <vladrodionov@gmail.com>
wrote:

> Matteo,
>
> For large cluster/table this one:
>
>  - the master will aggregate the result and verify the integrity
>
> looks like a real bottleneck.
>

the integrity verification is just file names verification not actual data
verification.


> Any other hidden serialized parts of the implementation?
>

nothing else I can think about


> On Tue, Mar 3, 2015 at 9:25 AM, Matteo Bertozzi <theo.bertozzi@gmail.com>
> wrote:
>
> > the high-level overview of snapshot is:
> >  - client ask the master to take a snapshot
> >  - the master lookup the RS that are hosting the regions for the
> specified
> > table
> >  - the master creates a znode to notify the RSs to take a snapshot
> >  - each RS involved will get notified and take the snapshot. which is
> flush
> > + writing a manifest
> >  - each RS involved will respond to the master
> >  - the master will aggregate the result and verify the integrity
> >  - snapshot complete
> >
> > so, the time required to take a snapshot is bounded by the slowest region
> > to flush/respond.
> > You can try with SKIP_FLUSH = true
> > also, if you grep Snapshot from the master log you can see what is taking
> > long.
> >
> > Matteo
> >
> >
> > On Tue, Mar 3, 2015 at 5:18 PM, Vladimir Rodionov <
> vladrodionov@gmail.com>
> > wrote:
> >
> > > Some discussions:
> > > http://comments.gmane.org/gmane.comp.java.hadoop.hbase.user/43616
> > >
> > > Any ideas why? It should not take 10s of seconds (unless we flush
> several
> > > GBs per server)
> > > I got info from my coworker that it is indeed slow (20+ sec on an
> almost
> > > empty table).
> > >
> > > I have not started testing myself yet but before I start digging into
> it
> > I
> > > would like to collect opinions from HBase folks.
> > >
> > > -Vlad
> > >
> >
>

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