Github user keith-turner commented on the pull request:
https://github.com/apache/accumulo/pull/96#issuecomment-215555038
> The original reason why the locators cache is cleared every hour is to
remove TabletLocators that refer to tablets that don't exist or are rarely
accessed, ya?
The clearing was added to clean tablet location cache memory populated
while processing bulk imports. If tablet servers were not processing bulk
imports, then only metadata table tablet locations would be cached.
>A WeakHashMap wouldn't work because it uses weak references for the keys
oh yeah, I was thinking it was based on values... but its not.
> What do you think of switching locators to a Guava cache with a 1 hour
timeout on entries since their last access?
May be good. Wouldn't we still need to prevent the guava cache from
removing tablet locators that are referenced outside the cache? I looked at
the Gauva cache javadoc and saw it supports weakValues() and softValues() based
caches. Based on past experience (that I just remembered) I am thinking weak
references may be bad, it seems like weak references are collected aggressively
(when only referenced by the cache). Clearing the cache too aggressively would
not be good for performance SoftReferences would not suffer from the
aggressive collection problem, but soft refs have their own problems.
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