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From Shu Zhang <szh...@mediosystems.com>
Subject RE: propertyfilesnitch problem
Date Wed, 09 Nov 2011 23:27:22 GMT
Hi, sorry to ask again, but I'm having trouble getting to the bottom of this...

Does anyone else see this? When dynamic snitch is turned off, the performance of LOCAL_QUORUM
operations is as bad as QUORUM. The property file snitch appears to be properly configured.
Any suggestions on how I can investigate further would be greatly appreciated.
________________________________________
From: Shu Zhang [szhang@mediosystems.com]
Sent: Monday, November 07, 2011 6:07 PM
To: user@cassandra.apache.org
Subject: propertyfilesnitch problem

Hi,

We have a 2 DC setup on version 0.7.9 and have observed the following:
1. Using a property file snitch, with dynamic snitch turned on. The performance of LOCAL_QUORUM
operations is poor for a while (around a minute) after a cluster restart before drastically
improving.
2. With the same setup, after each period as defined by dynamic_snitch_reset_interval_in_ms,
the LOCAL_QUORUM performance greatly degrades before drastically improving again within a
minute.
3. With the dynamic snitch turned off, LOCAL_QUORUM operations perform extremely poorly...
same as the 1st minute after a restart.
4. With dynamic snitch turned on, QUORUM operations' performance is about the same as using
LOCAL_QUORUM when the dynamic snitch is off or the first minute after a restart with the snitch
turned on.

All of this seem to point to LOCAL_QUORUM operations not differentiating our DCs using the
property file snitch and its performance effectively degrades to that of QUORUM when dynamic
snitch doesn't have appropriate scores.

Our main concern is the performance degradation at the periods defined by dynamic_snitch_reset_interval_in_ms.

The DynamicEndpointSnitch in steady state assigns scores that matches the DCs we've configured
through the network topology property file.

Our network topology property file appears to be properly configured and have been confirmed
through the EndpointSnitchInfo mbean.

Please advice.

Thanks,
Shu
Medio Systems

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