server sizing

On: http://docs.couchbase.com/couchbase-devguide-2.2/#storing-data

There is a sample calculation:
"One hundred million keys which are 70 Bytes each plus meta data at 54 Bytes each will require about 23 GB of RAM for document meta data"

Can somebody help with the math....
(70+54) * 100000000 / 1024/1024/1024 = 11.55 GiB
(70+54) * 100000000 / 1000/1000/1000 = 12.4 GB

How do you get to 23 GB?

I think they might be multiplying by 2 because of replica.

1 Answer

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The full text from the documentation

"Be aware of key and metadata size if you are handling millions of documents or more. Couchbase Server keeps all keys and metadata in RAM and does not remove them to create more space in RAM. One hundred million keys which are 70 Bytes each plus meta data at 54 Bytes each will require about 11.2 GB of RAM for a cluster. This figure does not include caching any values or replica copies of data, if you consider these factors, you would need over 23 GB."