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From Yang <teddyyyy...@gmail.com>
Subject Re: Replicate On Write behavior
Date Thu, 01 Sep 2011 20:17:10 GMT
when Cassandra reads, the entire CF is always read together, only at the
hand-over to client does the pruning happens

On Thu, Sep 1, 2011 at 11:52 AM, David Hawthorne <dhawth@gmx.3crowd.com>wrote:

> I'm curious... digging through the source, it looks like replicate on write
> triggers a read of the entire row, and not just the columns/supercolumns
> that are affected by the counter update.  Is this the case?  It would
> certainly explain why my inserts/sec decay over time and why the average
> insert latency increases over time.  The strange thing is that I'm not
> seeing disk read IO increase over that same period, but that might be due to
> the OS buffer cache...
>
> On another note, on a 5-node cluster, I'm only seeing 3 nodes with
> ReplicateOnWrite Completed tasks in nodetool tpstats output.  Is that
> normal?  I'm using RandomPartitioner...
>
> Address         DC          Rack        Status State   Load            Owns
>    Token
>
>  136112946768375385385349842972707284580
> 10.0.0.57    datacenter1 rack1       Up     Normal  2.26 GB         20.00%
>  0
> 10.0.0.56    datacenter1 rack1       Up     Normal  2.47 GB         20.00%
>  34028236692093846346337460743176821145
> 10.0.0.55    datacenter1 rack1       Up     Normal  2.52 GB         20.00%
>  68056473384187692692674921486353642290
> 10.0.0.54    datacenter1 rack1       Up     Normal  950.97 MB       20.00%
>  102084710076281539039012382229530463435
> 10.0.0.72    datacenter1 rack1       Up     Normal  383.25 MB       20.00%
>  136112946768375385385349842972707284580
>
> The nodes with ReplicateOnWrites are the 3 in the middle.  The first node
> and last node both have a count of 0.  This is a clean cluster, and I've
> been doing 3k ... 2.5k (decaying performance) inserts/sec for the last 12
> hours.  The last time this test ran, it went all the way down to 500
> inserts/sec before I killed it.

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