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Subject: Re: Would it be possible to do a ColumnCache?
From: =?ISO-8859-1?Q?H=E9ctor?= Izquierdo Seliva <izquierdo@strands.com>
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Date: Thu, 21 Oct 2010 17:46:14 +0200
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When I say "rows in the slice" I mean "columns in the slice", sorry for
the typo.

El jue, 21-10-2010 a las 17:44 +0200, Héctor Izquierdo Seliva escribió:
> El jue, 21-10-2010 a las 00:02 -0500, Jonathan Ellis escribió:
> > I don't think it's possible.  Cassandra's data model means you can't
> > know what columns are present in a row, so if you query, say, name and
> > birthdate from your users column family and only the name column is in
> > the cache for the row you are querying, does that mean that birthdate
> > doesn't exist in that row?  Or just that it's not cached?  You don't
> > know, so you'd have to do a full read every time.  Similar
> > difficulties arise with slices.
> 
> I was thinking in a column cache to be used when you need a slice of a
> row, where you'd ask the cache for all the rows in the slice, and then
> read from disk whichever rows weren't in cache. If the columns you want
> don't exist, you still hit the disk, but you get a nice speedup for
> existing columns. 
> 
> If you want write-through cache then things complicate a bit, but it
> should be doable.
> 
> The question is, would the performance improvement justifies the
> increase in complexity?
> 
> 
> 
> > 
> > 2010/10/20 Héctor Izquierdo Seliva <izquierdo@strands.com>:
> > > Hi. Before wasting time in something that might not be feasible at the
> > > moment, I wanted to ask the devs if a column cache would be possible
> > > (instead of a whole row cache). This would allow users with fat rows to
> > > also use a cache and reduce latency for hot data.
> > >
> > > If this is possible, i'd appreciate some hints about where to dig.
> > >
> > > Thanks for your time!
> > >
> > >
> > 
> > 
> > 
> 
>