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From Tyler Hobbs <>
Subject Re: Combining all CFs into one big one
Date Sun, 01 May 2011 19:43:54 GMT
On Sun, May 1, 2011 at 2:16 PM, Jake Luciani <> wrote:

> On Sun, May 1, 2011 at 2:58 PM, shimi <> wrote:
>> On Sun, May 1, 2011 at 9:48 PM, Jake Luciani <> wrote:
>>> If you have N column families you need N * memtable size of RAM to
>>> support this.  If that's not an option you can merge them into one as you
>>> suggest but then you will have much larger SSTables, slower compactions,
>>> etc.
>>> I don't necessarily agree with Tyler that the OS cache will be less
>>> effective... But I do agree that if the sizes of sstables are too large for
>>> you then more hardware is the solution...
>> If you merge CFs which are hardly accessed with one which are accessed
>> frequently, when you read the SSTable you load data that is hardly accessed
>> to the OS cache.
>  Only the rows or portions of rows you read will be loaded into the OS
> cache.  Just because different rows are in the same file doesn't mean the
> entire file is loaded into the OS cache.  The bloom filter and index file
> will be loaded but those are not large files.

Right -- it does depend on the page size and the average amount of data
read.  The effect will be more pronounced on CFs with small rows that those
with wide rows.

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