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From Devaraj Das <d...@hortonworks.com>
Subject Re: [PROPOSAL] HBASE-10070 branch
Date Thu, 16 Jan 2014 02:29:24 GMT
On Wed, Jan 15, 2014 at 4:43 PM, Elliott Clark <eclark@apache.org> wrote:
> On Wed, Jan 15, 2014 at 3:57 PM, Enis Söztutar <enis.soz@gmail.com> wrote:
>> I am afraid, it is not coprocessors or current set of plugins only. We need
>> changes in the
>> RPC, meta, region server, LB and master. Since we cannot easily get hooks
>> into all these in
>> a clean manner, implementing this purely outside would be next to
>> impossible.
> I'm pretty unconvinced that this is the correct way forward.  It seems to
> introduce a lot of risk without a lot of gain.  Right now to me the 100%
> correct way forward is through paxos.  That's a lot of work but it has the
> most payoff in the end.  It will allow much faster recovery, much easier
> read sharding, it allows the greatest flexibility on IO.

Elliott, if I am not mistaken, we will need the replica management
work for the Paxos case as well. A lot of the work done in HBASE-10070
(to start with, the master/loadbalancer side of the region-replica
management work) would be leveraged if we choose to implement Paxos.

> On the other end of the spectrum is something like MySQL/Postgres read
> slaves (either tables or clusters).  Read slaves built on top of what's
> currently there seem to give all of the benefits of read slaves built into
> the current HBase without all of the risk. Sharding on top of the already
> built datastore is a pretty well known and well understood problem.  There
> are lots of great example of making this scale to pretty insane heights.
>  You lose very little flexibility and incur almost not risk to the
> stability of HBase.

We have gone over this point before. We are trying to address the
issue within a single cluster. We don't want to create more storage
overhead if we can help it (which we would have if we did
intra-cluster replication).
Again the default behavior of single replica per region, etc. is kept
intact. This should be true even from the stability point of view.

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