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From Gary Dusbabek <>
Subject Re: Time to wait for CF to be consistent after stopping writes.
Date Wed, 27 Oct 2010 13:24:42 GMT
On Wed, Oct 27, 2010 at 05:08, Utku Can Top├žu <> wrote:
> Hi,
> For a columnfamily in a keyspace which has RF=3, I'm issuing writes with
> ConsistencyLevel.ONE.
> in the configuration I have:
> - memtable_flush_after_mins : 30
> - memtable_throughput_in_mb : 32
> I'm writing to this columnfamily continuously for about 1 hour then stop
> writing.
> So the question is:
> How long should I wait after stopping writes to that particular CF so that
> all writes take place and data contained in the CF will be consistent.

There is no way to determine this precisely.  Depending on your nodes
and network it could be as short as a few milliseconds or much longer.

> Which metrics should I be checking to ensure that the CF is now consistent?

Execute a read using ConsistencyLevel.ALL.  If the value is not yet
consistent, read repair will ensure that it soon will be.  Another
approach is to write using ConsistencyLevel.ALL, although that would
decrease your write throughput.

> And additionally if I was using ConsistencyLevel.QUORUM or
> ConsistencyLevel.ALL would it make a difference?


> Would reducing the RF=3 to RF=1 would it make my life on this decision
> easier?

It would make determining consistency better, but RF=1 isn't going to
be very fault tolerant.


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