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From Ertio Lew <>
Subject Re: Merging the rows of two column families(with similar attributes) into one ??
Date Sat, 05 Feb 2011 06:28:48 GMT
Thanks Tyler !

I could not fully understand the reason why more no of column families
would mean more memory.. if you have under control parameters like
memtable_throughput & memtable_operations which are set per column
family basis then you can directly control & adjust by splitting the
memory space between two CFs in proportion to what you would do in
single CF.
Hence there should be no extra memory consumption for multiple CFs
that have been split from single one??

Regarding the compactions, I think even if they are more the size of
the SST files to be compacted is smaller as the data has been split
into two.
Then more compactions but smaller too!!

Then, provided the same amount of data, how can greater no of column
families could be a bad option(if you split the values of parameters
for memory consumption proportionately) ??


On Sat, Feb 5, 2011 at 10:43 AM, Tyler Hobbs <> wrote:
>> I read somewhere that more no of column families is not a good idea as
>> it consumes more memory and more compactions to occur
> This is primarily true, but not in every case.
>> But the caching requirements may be different as they cater to two
>> different features.
> This is a great reason to *not* merge them.  Besides the key and row caches,
> don't forget about the OS buffer cache.
>> Is it recommended to merge these two column families into one ?? Thoughts
>> ?
> No, this sounds like an anti-pattern to me.  The overhead from having two
> separate CFs is not that high.
> --
> Tyler Hobbs
> Software Engineer, DataStax
> Maintainer of the pycassa Cassandra Python client library

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