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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: system_* consistency level?
Date Wed, 20 Apr 2011 22:05:07 GMT
See the comments for describe_schema_versions.

On Wed, Apr 20, 2011 at 4:59 PM, William Oberman
<oberman@civicscience.com> wrote:
> Hi,
>
> My unit tests started failing once I upgraded from a single node cassandra
> cluster to a full "N" node cluster (I'm starting with 4).  I had a few
> various bugs, mostly due to forgetting to read/write at a quorum level in
> places I needed stronger consistency guarantees.  But, I kept getting
> random, intermittent failure (the worst kind).  I'm 99% sure I see why,
> after some painful debugging, but I don't know what to do about it.  The
> basic flaw in my understanding of cassandra seems to boil down to: I thought
> system mutations of keyspaces/column families where of a stronger
> consistency than ONE, but that appears to not be true.  Any way for me to
> update a cluster at something more like QUORUM?
>
> The basic idea is in my unit test.setup() I clone my real keyspace as
> keyspace_UUID (with all of the exact same CFs) to get a fresh space to play
> in.  In a single node environment, no issues.  But, in a cluster, it seems
> that it takes a while for the system_add_keyspace call to propagate.  No
> worries I think, I just modify my setup() to do
> describe_keyspace(keyspace_UUID) in a while loop until the cluster is
> ready.  My random failures drop considerably, but every once and awhile I
> see a similar kind of failure.  Then I find out that schema updates seem to
> propagate on a per node basis.  At least, that's what I have to assume as
> I'm using phpcassa which uses a connection pool, and I see in my logging
> that my setup() succeeds because one connection in the pool sees the new
> keyspace, but when my tests run I grab a connection from the pool that is
> missing it!
>
> Do I have a solution other than changing my setup yet again to loop over all
> cassandra servers doing a describe_keyspace()?
>
> --
> Will Oberman
> Civic Science, Inc.
> 3030 Penn Avenue., First Floor
> Pittsburgh, PA 15201
> (M) 412-480-7835
> (E) oberman@civicscience.com
>



-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com

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