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From aledsage <...@git.apache.org>
Subject [GitHub] brooklyn-server issue #331: Fix some memory leaks and better memory usage lo...
Date Fri, 23 Sep 2016 12:30:09 GMT
Github user aledsage commented on the issue:

    https://github.com/apache/brooklyn-server/pull/331
  
    The idea behind `MemoryUsageTracker. forceClearSoftReferences()` makes sense, but feels
a little scary! The code looks fine though. It will never be enabled in production, only when
profiling, so I'm happy to merge it.
    
    The other additions to the regular output of `BrooklynGarbageCollection` look sensible.
    
    ---
    What about the removal of `MemoryUsageTracker.getBytesUsed()`? Should we either delete
that entirely, or leave it in the output of the `BrooklynGarbageCollection`? It's useful to
know how big the soft references are (as long as we call it consistently enough).
    
    It currently is a bit confusing having `MemoryUsageTracker.SOFT_REFERENCES` and `MemoryUsageTracker.SoftUsageTracker`
(which are unrelated to each other).
    
    You're right to mark that as `@Beta`!
    
    ---
    If investigating a memory leak, then `jmap -histo:live <pid>` and `jmap -heap <pid>`
will both include soft references. A subsequent analysis of the output file from `jmap -dump:live,format=b,file=heap.bin
<pid>` will allow you to filter out the soft references, but that's fiddlier.
    
    Looking at `jmap -histo:live` and manually excluding the stdout/stderr of tasks (so streams
/ byte arrays) will give a good indication of all non-soft references (but you may accidentally
ignore things that are not soft-references).
    
    Much longer term, we should consider how best to store historic task details (e.g. in
riak) and a better deletion policy for them. But that is a much bigger undertaking.


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