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.Langston@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