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Re: Multiple cluster for a single application


Interesting approach Eric, thanks for sharing that.

Regarding this:  

> I've read documents recommended to use clusters with less than 50 or 100 nodes (Netflix got hundreds of clusters with less 100 nodes on each).

Not sure where you read that, but it's nonsense.  We work with quite a few clusters that are several hundred nodes each.  Your problems can get a bit amplified, for instance dynamic snitch can make a cluster perform significantly worse than if you just flat out disable it, which is what I usually recommend.  

I'm curious how you arrived at the estimate of needing > 100 nodes.  Is that due to space constraints or performance ones?  



On Wed, Nov 7, 2018 at 12:52 PM Eric Stevens <mightye@xxxxxxxxx> wrote:
We are engaging in both strategies at the same time:

1) We call it functional sharding - we write to clusters targeted according to the type of data being written.  Because different data types often have different workloads this has the nice side effect of being able to tune each cluster according to its workload.  Your ability to grow in this dimension is limited by the number of business object types you're recording.

2) We write to clusters sharded by time.  Our objects are network security events, so there's always an element of time.  We encode that time into deterministic object IDs so that we are able to identify in the read path which shard to direct the request to by extracting the time component.  This basic idea should be able to work any time you're able to use surrogate keys instead of natural keys.  If you are using natural keys, you may be facing an unpleasant migration should you need to increase the number of shards in this dimension.

Our reason for engaging in the second strategy was not purely Cassandra's fault, rather we were using DSE with a search workload, and the cost of rebuilding Solr indexes on streaming operations (such as adding nodes to an existing cluster) required enough resources that we found it prohibitive.  That's because the bootstrapping node was also taking a production write workload, and we didn't want to run our cluster with enough overhead that a node could bootstrap and take production workload at the same time.

For vanilla Cassandra workloads we have run clusters with quite a bit more nodes than 100 without any appreciable trouble.  Curious if you can share documents about clusters over 100 nodes causing troubles for users.  I'm wondering if it's related to node failure rate combined with vnodes meaning that several concurrent node failures cause a part of the ring to go offline too reliably.

On Mon, Nov 5, 2018 at 7:38 AM onmstester onmstester <onmstester@xxxxxxxx.invalid> wrote:
Hi,

One of my applications requires to create a cluster with more than 100 nodes, I've read documents recommended to use clusters with less than 50 or 100 nodes (Netflix got hundreds of clusters with less 100 nodes on each).
Is it a good idea to use multiple clusters for a single application, just to decrease maintenance problems and system complexity/performance?
If So, which one of below policies is more suitable to distribute data among clusters and Why?
1. each cluster' would be responsible for a specific partial set of tables only (table sizes are almost equal so easy calculations here) for example inserts to table X would go to cluster Y
2. shard data at loader level by some business logic grouping of data, for example all rows with some column starting with X would go to cluster Y

I would appreciate sharing your experiences working with big clusters, problem encountered and solutions.

Thanks in Advance

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