Paul Ferraro closed MODCLUSTER-288.
You're right that this metric isn't going to be very informative for most users.
JVM memory usage is typically more relevant, but that's what the
HeapMemoryUsageLoadMetric is for. This metric would only really be used for a system that
performs a significant amount of extra-jvm work, e.g. starting external processes, etc,
where free system memory is of relevance.
SystemMemoryUsageLoadMetric is not correct on Linux/Unix
Issue Type: Bug
Affects Versions: 1.0.10, 1.1.0.Final, 1.1.1.Final, 1.2.0.Final
Environment: Linux/Unix operating systems with standard memory management
Reporter: Michal Babacek
Assignee: Paul Ferraro
I am convinced that the
is of no use to anyone.
I have tested it by allocating some memory outside the JVM control with
The results from Mod_cluster are such that the system is almost fully loaded all the time
despite the fact that I work with 8GB RAM box with almost nothing running on it.
displays time on X axis and (100-(Load from Mod_cluster)) on Y axis. As you may observe,
all 4 nodes appear to be under full load all the time and there is a spike on each of
them. This spike represents a period of time when the aforementioned
was called with the following setting:
What had happened is that kernel has cleared some cache and garbage data from the RAM in
order to accommodate new demands, so by the time I freed the memory, there was all of
sudden actually more free RAM then before.
The actual problem with the current
is that this code:
public static final String FREE_MEMORY = "FreePhysicalMemorySize";
public static final String TOTAL_MEMORY = "TotalPhysicalMemorySize";
double free = ((Number) this.server.getAttribute(name, FREE_MEMORY)).doubleValue();
double total = ((Number) this.server.getAttribute(name, TOTAL_MEMORY)).doubleValue();
return (total - free) / total;
Is somewhat similar to this (on 8GB RAM machine with almost nothing running on at the
[karm@killerbox karm]$ free -m
total used free shared buffers cached
Mem: 7933 6755 1177 0 44 141
-/+ buffers/cache: 6569 1363
Swap: 16383 58 16325
Obviously, this does not mean that I could get only 1177MB of RAM if I want to. The
"free" actually means "wasted". The majority of RAM is being used as
cache. If I ask for e.g. 2GB, I am gonna get them, because kernel will simply sacrifice
some cache, clears some garbage from RAM and free up space so as to accommodate my
So, according to my opinion, on a sane, well-behaving caching operating system, the
will always show ~ 98% RAM usage.
Due to this fact, this metric is unlikely to be of some use to anyone on Linux/UNIX. What
do you think?
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