To get an accurate picture you should force a full GC on each node, the heap utilization can be misleading since there can be a lot of things in the heap with no strong references.
There is a number of factors that can lead to this. For a true comparison I would recommend using jconsole and call dumpHeap on com.sun.management:type=HotSpotDiagnostic with the 2nd param true (force GC). Then open the heap dump up in a tool like yourkit and you will get a better comparison and also it will tell you what it is that's taking the space. Chris From: Langston, Jim [mailto:jim.langs...@compuware.com] Sent: Tuesday, September 03, 2013 8:20 AM To: user@cassandra.apache.org Subject: read ? Hi all, Quick question I currently am looking at a 4 node cluster and I have currently stopped all writing to Cassandra, with the reads continuing. I'm trying to understand the utilization of memory within the JVM. nodetool info on each of the nodes shows them all growing in footprint, 2 of the three at a greater rate. On the restart of Cassandra each were at about 100MB, after 2 days, each of the following are at: Heap Memory (MB) : 798.41 / 3052.00 Heap Memory (MB) : 370.44 / 3052.00 Heap Memory (MB) : 549.73 / 3052.00 Heap Memory (MB) : 481.89 / 3052.00 Ring configuration: Address Rack Status State Load Owns Token 127605887595351923798765477786913079296 x 1d Up Normal 4.38 GB 25.00% 0 x 1d Up Normal 4.17 GB 25.00% 42535295865117307932921825928971026432 x 1d Up Normal 4.19 GB 25.00% 85070591730234615865843651857942052864 x 1d Up Normal 4.14 GB 25.00% 127605887595351923798765477786913079296 What I'm not sure of is what the growth is different between each ? and why that growth is being created by activity that is read only. Is Cassandra caching and holding the read data ? I currently have caching turned off for the key/row. Also as part of the info command Key Cache : size 0 (bytes), capacity 0 (bytes), 0 hits, 0 requests, NaN recent hit rate, 14400 save period in seconds Row Cache : size 0 (bytes), capacity 0 (bytes), 0 hits, 0 requests, NaN recent hit rate, 0 save period in seconds Thanks, Jim
