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From Paul Prescod <>
Subject KeysCached and sstable
Date Wed, 14 Apr 2010 15:23:07 GMT
The inline docs say:

       ~ The optional KeysCached attribute specifies
       ~ the number of keys per sstable whose locations we keep in
       ~ memory in "mostly LRU" order.

There are a few confusing bits in that sentence.

 1. Why is "keys per sstable" rather than "keys per column family". If
I have 7 SSTable files and I set KeysCached to 10000, will I have
70000 keys cached? If so, why? What is the logical relationship here?

 2. What makes the algorithm "mostly LRU" rather than just LRU?

 3. Is it accurate the say that the goal of the Key Cache is to avoid
looking through a bunch off SSTable's Bloom Filters? (how big do the
bloom filters grow to...too much to be cached themselves?)

I'd like to document the detail.

 Paul Prescod

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