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From Ravikumar Govindarajan <>
Subject Re: Shard takeover behavior
Date Wed, 05 Mar 2014 07:07:33 GMT

I find that shard-servers are registered as ephemeral nodes in ZK.

Does this mean that, when a shard-server process gets killed {OOM-killer
etc...}, the layout gets re-built?

Rolling-upgrade or restarts will be performed in shard-servers one by one.
Will the layout get re-built here also? [In this case, layout calculation
is performed multiple times in a very short-span of time]


On Mon, Feb 17, 2014 at 9:20 PM, Ravikumar Govindarajan <> wrote:

> This will cancel all current queries with a
>> BlurException of type BACK_PRESSURE, the controller will automatically
>> retry the queries that were cancelled
> This is a real nice feature and most handy in production too, as a
> protection gainst both intentional and un-intentional bad queries
>  Since every update to the index via thrift mutates are committed and
>> syncedto HDFS, it possible to have other shards follow the lead shard
>> (the
> writer)
> I think I am back to data-locality we previously discussed with your "lead
> shard" remark. It is now possible to pin data-nodes to a file during writes
> in hadoop.
> We can always pin a shard to 3 shard-servers [assuming shard-server is run
> in datanodes] and persist this ZK. Failures can be easily handled using
> this info
> The big advantage of this method is, even in case of failures
> short-circuit reads are always utilized. I know you are not a big-fan of
> it, but still is it worthwhile to pursue it?
> One downside to this approach is, cluster balance might get skewed and
> need to be properly handled in HDFS
> --
> Ravi

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