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From: jeff saremi <jeffsaremi@hotmail.com>
To: "user@hbase.apache.org" <user@hbase.apache.org>
Subject: Re: On HBase Read Replicas
Thread-Topic: On HBase Read Replicas
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Date: Thu, 2 Mar 2017 16:46:45 +0000
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Thank you Biju

________________________________
From: Biju N <bijuatapache@gmail.com>
Sent: Wednesday, March 1, 2017 2:11:15 PM
To: user@hbase.apache.org
Subject: Re: On HBase Read Replicas

From the table definition. For e.g.
https://hbase.apache.org/apidocs/org/apache/hadoop/hbase/HTableDescriptor.h=
tml#getRegionReplication--

On Tue, Feb 28, 2017 at 3:30 PM, jeff saremi <jeffsaremi@hotmail.com> wrote=
:

> Enis
>
> just one more question. How would i go about getting the count of the
> replica's for a table or columngroup? thanks
>
> ________________________________
> From: Enis S=F6ztutar <enis.soz@gmail.com>
> Sent: Wednesday, February 22, 2017 1:38:41 PM
> To: hbase-user
> Subject: Re: On HBase Read Replicas
>
> If you are doing a get to a specific replica, it will execute as a read
> with retries to a single "copy". There will not be any backup / fallback
> RPCs to any other replica.
>
> Only in timeline consistency mode there will be fallback RPCs.
>
> Enis
>
> On Sun, Feb 19, 2017 at 9:43 PM, Anoop John <anoop.hbase@gmail.com> wrote=
:
>
> > Thanks Enis.. I was not knowing the way of setting replica id
> > specifically..  So what will happen if that said replica is down at
> > the read time?  Will that go to another replica?
> >
> > -Anoop-
> >
> > On Sat, Feb 18, 2017 at 3:34 AM, Enis S=F6ztutar <enis.soz@gmail.com>
> wrote:
> > > You can do gets using two different "modes":
> > >  - Do a read with backup RPCs. In case, the algorithm that I have abo=
ve
> > > will be used. 1 RPC to primary, and 2 more RPCs after primary timeout=
s.
> > >  - Do a read to a single replica. In this case, there is only 1 RPC
> that
> > > will happen to that given replica.
> > >
> > > Enis
> > >
> > > On Fri, Feb 17, 2017 at 12:03 PM, jeff saremi <jeffsaremi@hotmail.com=
>
> > > wrote:
> > >
> > >> Enis
> > >>
> > >> Thanks for taking the time to reply
> > >>
> > >> So i thought that a read request is sent to all Replicas regardless.
> If
> > we
> > >> have the option of Sending to one, analyzing response, and then
> sending
> > to
> > >> another, this bodes well with our scenarios.
> > >>
> > >> Please confirm
> > >>
> > >> thanks
> > >>
> > >> ________________________________
> > >> From: Enis S=F6ztutar <enis.soz@gmail.com>
> > >> Sent: Friday, February 17, 2017 11:38:42 AM
> > >> To: hbase-user
> > >> Subject: Re: On HBase Read Replicas
> > >>
> > >> You can use read-replicas to distribute the read-load if you are fin=
e
> > with
> > >> stale reads. The read replicas normally have a "backup rpc" path,
> which
> > >> implements a logic like this:
> > >>  - Send the RPC to the primary replica
> > >>  - if no response for 100ms (or configured timeout), send RPCs to th=
e
> > other
> > >> replicas
> > >>  - return the first non-exception response.
> > >>
> > >> However, there is also another feature for read replicas, where you
> can
> > >> indicate which exact replica_id you want to read from when you are
> > doing a
> > >> get. If you do this:
> > >> Get get =3D new Get(row);
> > >> get.setReplicaId(2);
> > >>
> > >> the Get RPC will only go to the replica_id=3D2. Note that if you hav=
e
> > region
> > >> replication =3D 3, then you will have regions with replica ids: {0, =
1,
> 2}
> > >> where replica_id=3D0 is the primary.
> > >>
> > >> So you can do load-balancing with a get.setReplicaId(random() %
> > >> num_replicas) kind of pattern.
> > >>
> > >> Enis
> > >>
> > >>
> > >>
> > >> On Thu, Feb 16, 2017 at 9:41 AM, Anoop John <anoop.hbase@gmail.com>
> > wrote:
> > >>
> > >> > Never saw this kind of discussion.
> > >> >
> > >> > -Anoop-
> > >> >
> > >> > On Thu, Feb 16, 2017 at 10:13 PM, jeff saremi <
> jeffsaremi@hotmail.com
> > >
> > >> > wrote:
> > >> > > Thanks Anoop.
> > >> > >
> > >> > > Understood.
> > >> > >
> > >> > > Have there been enhancement requests or discussions on load
> > balancing
> > >> by
> > >> > providing additional replicas in the past? Has anyone else come up
> > with
> > >> > anything on this?
> > >> > > thanks
> > >> > >
> > >> > > ________________________________
> > >> > > From: Anoop John <anoop.hbase@gmail.com>
> > >> > > Sent: Thursday, February 16, 2017 2:35:48 AM
> > >> > > To: user@hbase.apache.org
> > >> > > Subject: Re: On HBase Read Replicas
> > >> > >
> > >> > > The region replica feature came in so as to reduce the MTTR and =
so
> > >> > > increase the data availability.  When the master region containi=
ng
> > RS
> > >> > > dies, the clients can read from the secondary regions.  But to
> keep
> > >> > > one thing in mind that this data from secondary regions will be
> bit
> > >> > > out of sync as the replica is eventual consistent.   Because of
> this
> > >> > > said reason,  change client so as to share the load across diff
> RSs
> > >> > > might be tough.
> > >> > >
> > >> > > -Anoop-
> > >> > >
> > >> > > On Sun, Feb 12, 2017 at 8:13 AM, jeff saremi <
> > jeffsaremi@hotmail.com>
> > >> > wrote:
> > >> > >> Yes indeed. thank you very much Ted
> > >> > >>
> > >> > >> ________________________________
> > >> > >> From: Ted Yu <yuzhihong@gmail.com>
> > >> > >> Sent: Saturday, February 11, 2017 3:40:50 PM
> > >> > >> To: user@hbase.apache.org
> > >> > >> Subject: Re: On HBase Read Replicas
> > >> > >>
> > >> > >> Please take a look at the design doc attached to
> > >> > >> https://issues.apache.org/jira/browse/HBASE-10070.
> > >> > >>
> > >> > >> Your first question would be answered by that document.
> > >> > >>
> > >> > >> Cheers
> > >> > >>
> > >> > >> On Sat, Feb 11, 2017 at 2:06 PM, jeff saremi <
> > jeffsaremi@hotmail.com>
> > >> > wrote:
> > >> > >>
> > >> > >>> The first time I heard replicas in HBase the following thought
> > >> > immediately
> > >> > >>> came to my mind:
> > >> > >>> To alleviate the load in read-heavy clusters, one could assign
> > Region
> > >> > >>> servers to be replicas of others so that the load is distribut=
ed
> > and
> > >> > there
> > >> > >>> is less pressure on the main RS.
> > >> > >>>
> > >> > >>> Just 2 days ago a colleague quoted a paragraph from HBase manu=
al
> > that
> > >> > >>> contradicted this completely. Apparently, the replicas do not
> help
> > >> > with the
> > >> > >>> load but they actually contribute to more traffic on the netwo=
rk
> > and
> > >> > on the
> > >> > >>> underlying file system
> > >> > >>>
> > >> > >>> Would someone be able to give us some insight on why anyone
> would
> > >> want
> > >> > >>> replicas?
> > >> > >>>
> > >> > >>> And also could one easily change this behavior in the HBase
> native
> > >> Java
> > >> > >>> client to support what I had been imagining as the concept for
> > >> > replicas?
> > >> > >>>
> > >> > >>>
> > >> > >>> thanks
> > >> > >>>
> > >> >
> > >>
> >
>

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