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From Stack <st...@duboce.net>
Subject Re: Suggested and max number of CFs per table
Date Thu, 17 Mar 2011 19:05:00 GMT
On Wed, Mar 16, 2011 at 11:30 PM, Otis Gospodnetic
<otis_gospodnetic@yahoo.com> wrote:
> If I'm reading http://hbase.apache.org/book/schema.html#number.of.cfs correctly,
> the advice is not to have more than 2-3 CFs per table?
> And what happens if I have say 6 CFs per table?
>
> Again if I read the above page correctly, the problem is that uneven data
> distribution will mean that whenever 1 of my CFs needs to be flushed, the
> remaining 5 CFs will also get flushed at the same time, and this may (or will?)
> trigger compaction for all CFs' files creating a sudden IO hit?
>
> Is there a good solution for this problem?
> Should one then have 6 different tables, each with just 1 CF instead of having 1
> table with 6 CFs?
>

Just to say that the reason we do not do > 3-4 CFs in a row well is
because we haven't done the work to make it work nicely.  As is, we do
dumb stuff like the above mentioned flush all CFs if one is at limit
even if others are small but then we also do stuff like serialize
lookups across the CFs instead of running queries in parallel if the
query is x-CFs (fixing this is one of the oldest issues in hbase).

St.Ack

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