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Performing in the cloud – network latency

To me, ‘cloud computing’ is renting a compute resource to perform a task. In order to use that compute resource, you need to instruct it to do something, which is typically done via the network. If the task the compute resource needs to fulfil is being an application server or being a client or both in the case of an application server that uses an Oracle database, the network latency between the client of the database and the database server is a critical property.

TCP Trace Analysis for NFS

How do we know where latency comes from when  there is a disparity in reported I/O latency on  the I/O subsystem and that of the latency reported on the  client box requesting the I/O.

For example if I have an Oracle database requesting I/O  and Oracle says an 8Kb request takes 50 ms yet the I/O storage subsystem says 8Kb I/Os are taking 1ms (averages) , then where does the 49  extra ms come from?

When the I/O subsystem is connected to Oracle via NFS  then there are a lot of layers that could be causing the extra latency.

Screen Shot 2013-08-23 at 1.35.20 PM

Where does the difference in latency come from between NFS Server and Oracle’s timing of pread?