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From Robert Coli <rc...@eventbrite.com>
Subject Re: large range read in Cassandra
Date Tue, 25 Nov 2014 19:45:59 GMT
On Tue, Nov 25, 2014 at 10:45 AM, Dan Kinder <dkinder@turnitin.com> wrote:

> To be clear, I expect this range query to take a long time and perform
> relatively heavy I/O. What I expected Cassandra to do was use auto-paging (
> https://issues.apache.org/jira/browse/CASSANDRA-4415,
> http://stackoverflow.com/questions/17664438/iterating-through-cassandra-wide-row-with-cql3)
> so that we aren't literally pulling the entire thing in. Am I
> misunderstanding this use case? Could you clarify why exactly it would slow
> way down? It seems like with each read it should be doing a simple range
> read from one or two sstables.
>

If you're paging through a single partition, that's likely to be fine. When
you said "range reads ... over rows" my impression was you were talking
about attempting to page through millions of partitions.

With that confusion cleared up, the likely explanation for lack of
availability in your case is heap pressure/GC time. Look for GCs around
that time. Also, if you're using authentication, make sure that your
authentication keyspace has a replication factor greater than 1.

=Rob

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