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From Jonathan Ellis <>
Subject Re: Read Latency
Date Fri, 15 Oct 2010 21:49:30 GMT
On Fri, Oct 15, 2010 at 2:21 PM, Wayne <> 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

> 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

Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support

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