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Date: Wed, 07 May 2014 14:28:21 -0400
From: Chris Burroughs <chris.burroughs@gmail.com>
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Subject: Re: row caching for frequently updated column
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You are close.

On 04/30/2014 12:41 AM, Jimmy Lin wrote:
> thanks all for the pointers.
>
> let' me see if I can put the sequences of event together ....
>
> 1.2
> people mis-understand/mis-use row cache, that cassandra cached the entire
> row of data even if you are only looking for small subset of the row data.
> e.g
> select single_column from a_wide_row_table
> will result in entire row cached even if you are only interested in one
> single column of a row.
>

Yep!

> 2.0
> and because of potential misuse of heap memory, Cassandra 2.0 remove heap
> cache, and only support off-heap cache, which has a side effect that write
> will invalidate the row cache(my original question)
>

"off-heap" is a common but misleading name for the 
SerializingCacheProvider.  It still stores several objects on heap per 
cached item and has to deser on read.

> 2.1
> the coming 2.1 Cassandra will offer true cache by query, so the cached data
> will be much more efficient even for wide rows(it cached what it needs).
>
> do I get it right?
> for the new 2.1 row caching, is it still true that a write or update to the
> row will still invalidate the cached row ?
>

I don't think "true cache by query" is an accurate description of 
CASSANDRA-5357.  I think it's more like a "head of the row" cache.