You can do gets using two different "modes": - Do a read with backup RPCs. In case, the algorithm that I have above will be used. 1 RPC to primary, and 2 more RPCs after primary timeouts. - 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 <jeffsar...@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 Söztutar <enis....@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 fine 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 the 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 = new Get(row); > get.setReplicaId(2); > > the Get RPC will only go to the replica_id=2. Note that if you have region > replication = 3, then you will have regions with replica ids: {0, 1, 2} > where replica_id=0 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.hb...@gmail.com> wrote: > > > Never saw this kind of discussion. > > > > -Anoop- > > > > On Thu, Feb 16, 2017 at 10:13 PM, jeff saremi <jeffsar...@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.hb...@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 containing 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 <jeffsar...@hotmail.com> > > wrote: > > >> Yes indeed. thank you very much Ted > > >> > > >> ________________________________ > > >> From: Ted Yu <yuzhih...@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 <jeffsar...@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 distributed and > > there > > >>> is less pressure on the main RS. > > >>> > > >>> Just 2 days ago a colleague quoted a paragraph from HBase manual that > > >>> contradicted this completely. Apparently, the replicas do not help > > with the > > >>> load but they actually contribute to more traffic on the network 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 > > >>> > > >