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From Mohit Anchlia <mohitanch...@gmail.com>
Subject Re: persistence in Hbase
Date Tue, 15 Jan 2013 03:38:26 GMT
This is a broad topic by itself. In short often people use battery backed
cache or leave the write cache disabled for such concern. There are various
factors involved when deciding if to leave caches enabled or not. Caches
are often good for OLTP type application or even light OLAP workload. But
for huge workload you might saturate caches and is better off leaving it
disabled, assuming these are not super computers with TBs of caches :).
There are other factors in play like number of replica copies you have and
what gurantees or SLA you have put in place around data availability and
loss in the event of site disaster. Most people are ok with some data loss
on site failure and leave caches enabled with multiple replica copies
enabled.

On Mon, Jan 14, 2013 at 7:19 PM, Otis Gospodnetic <
otis.gospodnetic@gmail.com> wrote:

> Hi,
>
> Just for my own edification - isn't data loss always going to be possible
> due to caches present in HDDs and inability(?) for force them to flush.  I
> believe I've read even fsync lies...
>
> Thanks,
> Otis
> --
> HBASE Performance Monitoring - http://sematext.com/spm/index.html
>
>
>
>
>
> On Thu, Jan 10, 2013 at 10:54 PM, lars hofhansl <larsh@apache.org> wrote:
>
> > Not entirely true, though.
> > Data is not sync'ed to disk, but only distributed to all HDFS replicas.
> > During a power outage event across all HDFS failure zones (such as a data
> > center) you can lose data.
> >
> >
> > -- Lars
> >
> >
> >
> > ----- Original Message -----
> > From: anil gupta <anilgupta84@gmail.com>
> > To: user@hbase.apache.org
> > Cc:
> > Sent: Thursday, January 10, 2013 2:38 PM
> > Subject: Re: persistence in Hbase
> >
> > Hi Mohammad,
> >
> > If the Write Ahead Log(WAL) is "turned on" then in **NO** case data
> should
> > be lost. HBase is strongly-consistent. If you know of any case when WAL
> is
> > turned on and data is lost then IMO that's a Critical bug in HBase.
> >
> > Thanks,
> > Anil Gupta
> >
> > On Thu, Jan 10, 2013 at 7:37 AM, Mohit Anchlia <mohitanchlia@gmail.com
> > >wrote:
> >
> > > Data also gets written in WAL. See:
> > >
> > > http://hbase.apache.org/book/perf.writing.html
> > >
> > > On Thu, Jan 10, 2013 at 7:36 AM, ramkrishna vasudevan <
> > > ramkrishna.s.vasudevan@gmail.com> wrote:
> > >
> > > > Yes definitely you will get back the data.
> > > >
> > > > Please read the HBase Book that explains things in detail.
> > > > http://hbase.apache.org/book.html.
> > > >
> > > > Regards
> > > > Ram
> > > >
> > > >
> > > > On Thu, Jan 10, 2013 at 8:48 PM, Panshul Gupta <panshul007@gmail.com
> >
> > > > wrote:
> > > >
> > > >  > Hello,
> > > > >
> > > > > I was wondering if it is possible that I have data stored in Hbase
> > > tables
> > > > > on my 10 node cluster. I switch off (power down) my cluster. When
I
> > > power
> > > > > up my cluster again, and run the HDFS and hadoop daemons, will the
> > > Hbase
> > > > > have my old data persisted in the form I left it?? or will I have
> to
> > re
> > > > > import all the data??
> > > > >
> > > > > Thankyou for the help.
> > > > >
> > > > > --
> > > > > Regards,
> > > > > Panshul.
> > > > > http://about.me/panshulgupta
> > > > >
> > > >
> > >
> >
> >
> >
> > --
> > Thanks & Regards,
> > Anil Gupta
> >
> >
>

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