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From: Jonathan Ellis <jbellis@gmail.com>
Date: Tue, 16 Feb 2010 19:17:15 -0600
Message-ID: <e06563881002161717o6bbeecd2u56f905eb2d86e547@mail.gmail.com>
Subject: Re: Testing row cache feature in trunk: write should put record in
	cache
To: cassandra-user@incubator.apache.org
Content-Type: text/plain; charset=ISO-8859-1

On Tue, Feb 16, 2010 at 7:11 PM, Weijun Li <weijunli@gmail.com> wrote:
> Just started to play with the row cache feature in trunk: it seems to be
> working fine so far except that for RowsCached parameter you need to specify
> number of rows rather than a percentage (e.g., "20%" doesn't work).

20% works, but it's 20% of the rows at server startup.  So on a fresh
start that is zero.

Maybe we should just get rid of the % feature...

> The problem is: when you write to Cassandra it doesn't seem to put the new
> keys in row cache (it is said to update instead invalidate if the entry is
> already in cache). Is it easy to implement this feature?

It's deliberately not done.  For many (most?) workloads you don't want
fresh writes blowing away your read cache.  The code is in
Table.apply:

                ColumnFamily cachedRow = cfs.getRawCachedRow(mutation.key());
                if (cachedRow != null)
                    cachedRow.addAll(columnFamily);

I think it would be okay to have a WriteThrough option for what you're
asking, though.

-Jonathan