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From Peter Lin <>
Subject Re: Second Cassandra users survey
Date Mon, 07 Nov 2011 13:26:23 GMT
This feature interests me, so I thought I'd add some comments.

Having used partition features in existing databases like DB2, Oracle
and manual partitioning, one of the biggest challenges is keeping the
partitions balanced. What I've seen with manual partitioning is that
often the partitions get unbalanced. Usually the developers take a
best guess and hope it ends up balanced.

Some of the approaches I've used in the past were zip code, area code,
state and some kind of hash.

So my question related deterministic sharding is this, "what rebalance
feature(s) would be useful or needed once the partitions get

Without a decent plan for rebalancing, it often ends up being a very
painful problem to solve in production. Back when I worked mobile
apps, we saw issues with how OpenWave WAP servers partitioned the
accounts. The early versions randomly assigned a phone to a server
when it is provisioned the first time. Once the phone was associated
to that server, it was stuck on that server. If the load on that
server was heavier than the others, the only choice was to "scale up"
the hardware.

My understanding of Cassandra's current sharding is consistent and
random. Does the new feature sit some where in-between? Are you
thinking of a pluggable API so that you can provide your own hash
algorithm for cassandra to use?

On Mon, Nov 7, 2011 at 7:54 AM, Daniel Doubleday
<> wrote:
> Allow for deterministic / manual sharding of rows.
> Right now it seems that there is no way to force rows with different row keys will be
stored on the same nodes in the ring.
> This is our number one reason why we get data inconsistencies when nodes fail.
> Sometimes a logical transaction requires writing rows with different row keys. If we
could use something like this:
> prefix.uniquekey and let the partitioner use only the prefix the probability that only
part of the transaction would be written could be reduced considerably.
> On Nov 1, 2011, at 11:59 PM, Jonathan Ellis wrote:
>> Hi all,
>> Two years ago I asked for Cassandra use cases and feature requests.
>> [1]  The results [2] have been extremely useful in setting and
>> prioritizing goals for Cassandra development.  But with the release of
>> 1.0 we've accomplished basically everything from our original wish
>> list. [3]
>> I'd love to hear from modern Cassandra users again, especially if
>> you're usually a quiet lurker.  What does Cassandra do well?  What are
>> your pain points?  What's your feature wish list?
>> As before, if you're in stealth mode or don't want to say anything in
>> public, feel free to reply to me privately and I will keep it off the
>> record.
>> [1]
>> [2]
>> [3]
>> --
>> Jonathan Ellis
>> Project Chair, Apache Cassandra
>> co-founder of DataStax, the source for professional Cassandra support

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