Re: [Postgres-xc-general] Node redundancy

On Wed, May 28, 2014 at 8:42 AM, Josh Berkus <jo...@ag...> wrote:
> On 05/26/2014 05:10 PM, Tim Uckun wrote:
>> Would it be possible to keep the shards in multiple data nodes so that if
>> one data node failed you'd just replace it when you can get around to it.
>
> Right, that's what I was describing.  It's the standard way to deal with
> redundancy in any parallel sharded database.
>
> The drawback is that it increases write times, because you can't count a
> write as saved unless all shards return.  This is why some databases
> (e.g. Cassandra) go one step further and have, say, each shard in 3
> places and only 2 need to return.  That gets way complicated though.
That's an additional overhead for 2PC as you need to wait for all the
nodes where a write occurred to have executed PREPARE. This also drops
any hopes to have autocommit write transactions, sinking performance
down particularly for OLTP apps, smth that XC plays well with by
design.
-- 
Michael