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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Read Latency
Date Sat, 16 Oct 2010 13:52:38 GMT
Stack trace from cassandra log?

On Sat, Oct 16, 2010 at 6:50 AM, Wayne <wav100@gmail.com> wrote:
> While doing a read I get a TApplicationException: Internal Error processing
> get_slice.
>
> On Fri, Oct 15, 2010 at 5:49 PM, Jonathan Ellis <jbellis@gmail.com> wrote:
>>
>> On Fri, Oct 15, 2010 at 2:21 PM, Wayne <wav100@gmail.com> wrote:
>> > The optimization definitely shaved off some time. Now it is running
>> > about 3x
>> > CFSTATS reported time. Below are the logs.
>> >
>> > There is a ~300ms time frame after the last ResponseVerbHandler prior to
>> > the
>> > resolver starting. Based on a quorum read the response resolver should
>> > kick
>> > after 2 reads come in correct? That would mean it waited 500ms before
>> > starting. Where is this time going?
>>
>> It's going to deserialize the replies to see if it has both the data
>> and enough digests to call resolve().  Then resolve deserializes them
>> a 2nd time, so there's an easy win there caching the first
>> deserialize, in the patch attached.  (Applies on top of the previous
>> one, which has been committed to the 0.6 svn branch at
>> https://svn.apache.org/repos/asf/cassandra/branches/cassandra-0.6.)
>>
>> > There is still the 3+ second delay between the last 2 entries. Is this
>> > the
>> > thrift server?
>>
>> It's converting the reply from Cassandra's internal representation to
>> thrift, and sending it to the client.  I suspect most of the time is
>> the actual sending/waiting for the client to read part.  Patch 2 also
>> includes a debug statement after the convert-to-thrift stage to
>> verify.
>>
>> --
>> Jonathan Ellis
>> Project Chair, Apache Cassandra
>> co-founder of Riptano, the source for professional Cassandra support
>> http://riptano.com
>
>



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

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