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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: repeated timeouts on quorum reads
Date Tue, 20 Oct 2009 01:33:49 GMT
On Mon, Oct 19, 2009 at 8:20 PM, Edmond Lau <edmond@ooyala.com> wrote:
> On Mon, Oct 19, 2009 at 6:01 PM, Jonathan Ellis <jbellis@gmail.com> wrote:
>> are there many rows like this?
>
> No - just a handful.  I'm able to repro by just launching 5 or 6
> threads that all read the same key.

Does it work if you just read one column? 2? 10?  If it does, how long
do those take?

Is the system busy with other reads or writes?

What resource do you see being used on the queried nodes?  cpu? (top)
disk? (iostat)

(Turn on debug logging to see which nodes are getting the queries, if
necessary.)

> I did find one point of note though.  Most of the quorum reads fail
> with 0 or 1 responses, but I see some that fail with 2 responses,
> which is odd given that only 2 responses were needed:

That means it got an answer from the 2 nodes computing hashes of the
answer for quorum purposes, but not the node that was tasked with
retrieving the actual data.

-Jonathan

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