Details
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Improvement
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Status: Reopened
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Major
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Resolution: Unresolved
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None
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Description
ZooKeeper is a complex distributed application. There are many reasons why any given read or write operation may become slow: a software bug, a protocol problem, a hardware issue with the commit log(s), a network issue. If the problem is constant it is trivial to come to an understanding of the cause. However in order to diagnose intermittent problems we often don't know where, or when, to begin looking. We need some sort of timestamped indication of the problem. Although ZooKeeper is not a datastore, it does persist data, and can suffer intermittent performance degradation, and should consider implementing a 'slow query' log, a feature very common to services which persist information on behalf of clients which may be sensitive to latency while waiting for confirmation of successful persistence.
Log the client and request details if the server discovers, when finally processing the request, that the current time minus arrival time of the request is beyond a configured threshold.
Look at the HBase responseTooSlow feature for inspiration.
