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From Bernd Fehling <>
Subject Re: swap and GC
Date Mon, 29 Jul 2013 13:17:50 GMT

Am 29.07.2013 14:46, schrieb Michael Ryan:
> This is interesting... How are you measuring the heap size?

This is displayed in jvisualvm and also logged with munin via JMX.


> -Michael
> -----Original Message-----
> From: Bernd Fehling [] 
> Sent: Monday, July 29, 2013 5:34 AM
> To:
> Subject: swap and GC
> Something interesting I have noticed today, after running my huge single index (49 mio.
records / 137 GB index) for about a week and replicating today I recognized that the heap
usage after replication did not go down as expected. Expected means if solr is started I have
a heap size between 4 to 5 GB and during the week under heavy load it might go up to 10 GB.
But after replication in offline mode it recovers to between 5 to 6 GB. But today it was not
going under 8 GB, even with forced GC from jvisualvm.
> So I first dropped the caches and tried again, no success.
> Next I turned off swap which took quite a while and turned it back on.
> This forced all content from swap back into memory. After calling Perform GC from jvisualvm
the heap dropped below 5 GB. Bingo!
> This leads me to the conclusion that java GC is not "seeing" or "reaching"
> objects which are located in swap.
> Anyone else seen this?
> As I am not short on memory or have any other problems I don't need any solution, but
if there are some users having memory problems with old objects in swap I would suggest a
cronjob after replication with swapoff/swapon and GC afterwards.
> Bernd

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