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From Michael Ryan <>
Subject RE: swap and GC
Date Mon, 29 Jul 2013 12:46:46 GMT
This is interesting... How are you measuring the heap size?


-----Original Message-----
From: Bernd Fehling [] 
Sent: Monday, July 29, 2013 5:34 AM
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.


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