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From dhutchis <...@git.apache.org>
Subject [GitHub] accumulo pull request: ACCUMULO-4229 BatchWriter Locator cache out...
Date Fri, 29 Apr 2016 16:12:21 GMT
Github user dhutchis commented on the pull request:

    https://github.com/apache/accumulo/pull/96#issuecomment-215784988
  
    > Instead of trying to wrap things up so that these classes can pseudo-safely hold
references to instances of `TabletLocator`
    
    The current PR does allow any class to safely hold a reference to a `TabletLocator`. 
It is simple and it works.  Don't you think it is better to permit classes the privilege of
holding a reference?  The Writer and Reader classes locally cache TabletLocators because they
write many entries to the same tablets from multiple threads, which could create lock contention
if they accessed the static locators every time.
    
    > While I'm dubious that it'd be a real concern, if we felt that this would have significant
performance impact (due to lock contention), then it should be possible to partially ameliorate
the hit by using a Guava Cache or even a ConcurrentHashMap.
    
    Yes, there are two items under discussion.  The first is to allow a class to hold a reference
to a TabletLocator without syncing issues caused by clearing of the static locators. The second
is to make locators into a Guava cache (or ConcurrentMap), which eliminates the synchronized
restriction on the TabletLocator methods.  
    
    The second item is not related to the original bug found for ACCUMULO-4229; rather, it
is an opportunity we found while thinking about the first item.  We could ignore it or act
on it.



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