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From Lance Norskog <>
Subject Re: SOLR memory usage jump in JVM
Date Wed, 19 Sep 2012 03:29:54 GMT
There is a known JVM garbage collection bug that causes this. It has to do with reclaiming
Weak references, I think in WeakHashMap. Concurrent garbage collection collides with this
bug and the result is that old field cache data is retained after closing the index. The bug
is more common with more processors doing GC simultaneously.

The symptom is that when you run a monitor, the memory usage rises to a peak, drops to a floor,
rises again in the classic sawtooth pattern. When the GC bug happens, the ceiling becomes
the floor, and the sawtooth goes from the new floor to a new ceiling. The two sizes are the
same. So, 2G to 5G, over and over, suddenly it is 5G to 8G, over and over.

The bug is fixed in recent Java 7 releases. I'm sorry, but I cannot find the bug number. 

----- Original Message -----
| From: "Yonik Seeley" <>
| To:
| Sent: Tuesday, September 18, 2012 7:38:41 AM
| Subject: Re: SOLR memory usage jump in JVM
| On Tue, Sep 18, 2012 at 7:45 AM, Bernd Fehling
| <> wrote:
| > I used GC in different situations and tried back and forth.
| > Yes, it reduces the used heap memory, but not by 5GB.
| > Even so that GC from jconsole (or jvisualvm) is "Full GC".
| Whatever "Full GC" means ;-)
| In the past at least, I've found that I had to hit "Full GC" from
| jconsole many times in a row until heap usage stabilizes at it's
| lowest point.
| You could check fieldCache and fieldValueCache to see how many
| entries
| there are before and after the memory bump.
| If that doesn't show anything different, I guess you may need to
| resort to a heap dump before and after.
| > But while you bring GC into this, there is another interesting
| > thing.
| > - I have one slave running for a week which ends up around 18 to
| > 20GB of heap memory.
| > - the slave goes offline for replication (no user queries on this
| > slave)
| > - the slave gets replicated and starts a new searcher
| > - the heap memory of the slave is still around 11 to 12GB
| > - then I initiate a Full GC from jconsole which brings it down to
| > about 8GB
| > - then I call optimize (on a optimized index) and it then drops to
| > 6.5GB like a fresh started system
| >
| >
| > I have already looked through Uwe's blog but he says "...As a rule
| > of thumb: Don’t use more
| > than 1/4 of your physical memory as heap space for Java running
| > Lucene/Solr,..."
| > That would be on my server 8GB for JVM heap, can't believe that the
| > system
| > will run for longer than 10 minutes with 8GB heap.
| As you probably know, it depends hugely on the usecases/queries: some
| configurations would be fine with a small amount of heap, other
| configurations that facet and sort on tons of different fields would
| not be.
| -Yonik

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