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From Bernd Fehling <>
Subject swap and GC
Date Mon, 29 Jul 2013 09:34:08 GMT
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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