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From "Keith Turner (JIRA)" <>
Subject [jira] [Created] (ACCUMULO-3983) Create tablet locator test suite
Date Mon, 31 Aug 2015 17:14:46 GMT
Keith Turner created ACCUMULO-3983:

             Summary: Create tablet locator test suite
                 Key: ACCUMULO-3983
             Project: Accumulo
          Issue Type: Improvement
            Reporter: Keith Turner

Looking up ACCUMULO-3982 made me take a look at the tablet locator source code.  When I was
looking at the code, I thought it would be nice if there were more parallelism in doing metadata
lookups (there is a write lock for updating the cache).  However this can be tricky because
if 100 threads need the same info thats not in the cache we do not want to lookup that information
100 times in metadata.  This made me think we probably need a test for the locator that measures
certain things under different circumstances.

For example we probably want to measure the following things :
  * Total cache memory usage
  * Number of lookups made to the metadata table
  * Response time of cache

Would want to run at least the following scenarios when measuring the above.
  * N threads lookup N different tablet locations against empty cache and populate cache
  * N threads lookup 1 tablet location against empty cache and populated cache
  * N threads invalidate N key extents and request location
  * N threads invalidate 1 key extents and request location

More scenarios would be needed. 

Ideally an implementation of tablet locator would minimize the time it take a thread to get
a response and it would minimize the number of metadata table request.  Hopefully having this
test suite could drive better implementations.  Need to be careful that the test scenarios
are realistic.  

Would probably want to make the test suite capable of running on multiple machines in-order
to properly simulate sharing the metadata table.

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