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From Sylvain Lebresne <sylv...@yakaz.com>
Subject Re: High read latency
Date Fri, 04 Jun 2010 08:13:17 GMT
As written in the third point of
http://wiki.apache.org/cassandra/CassandraLimitations,
right now, super columns are not indexed and deserialized fully when you access
them. Another way to put it is, you'll want to user super columns with
only a relatively
small number of columns in them.
Because in you example, even if you read 1 column in 1 row, the full
supercolumn
where this column is is read from disk. Now, 50ms to read 50000 records isn't
necessarily too bad.

ColumnIndexSizeInKB will not help here (as superColumns are not indexed anyway)
and your only way out is to change you model so that you don't have
super columns
with so many columns.

On Fri, Jun 4, 2010 at 8:26 AM, Ma Xiao <maxiao@robowork.com> wrote:
> we have a SupperCF which may have up to 1000 supper columns and 50000
> clumns for each supper column, the read latency may go up to 50ms
> (even higher), I think it's a long time to response, how to tune the
> storage config to optimize the performace? I read the wiki,
> <ColumnIndexSizeInKB> may help to do this, supose that by asign a big
> value to this( 20000 ex. ), no row and reach this limit so it never
> generate a index for a row. In our production scenario, we only access
> 1 row at a time and with up to 1000 columns slice retuned.  Any
> suggestion?
>

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