<charlie_li...@carehart.org> wrote:
> Well, sure, by the time you get in to view the FR interface, things could be
> different than what you saw in the alert.

> But you should be able to see the exact time in the alert (don't go by the
> time you "received" the email but the time shown *within* the alert, which
> shows when it was generated by FR), and then go to the FR interface (system
> metrics or resources>memory graph), or the logs, to see what they show the
> memory use was at that time.

> Note, too, that you could be looking at 2 different servers: the alert could
> come from one and you may be looking at the FR instance for another. Just
> saying: look very closely at where the alert says it's coming from, and be
> sure you see that same instance name in the top left corner of FR when
> viewing it. :-)

> Finally, as just a reminder for everyone, be careful also when setting the
> memory alert to be sure to set the amount as the "amount of free memory
> below which it should alert" (so 20, if you want an alert when free memory
> falls below 20%). Some instead mistakenly think it's the "amount above which
> used memory it should alert", and they would set it to 80. In that case,
> you'll be getting alerts all the time, whenever the heap is above 20% used.
> Very common mistake, but I'll trust, Chris, from your wording, that that's
> not what's happening for you. Just pointing it out for others while we're on
> the topic.

> And I would note that a number like 5 (as he says he's using, for 5% free
> memory) is better than most would suspect. You might think, "well I don't
> want to be notified only when there's 5% left. I'd like to be told when
> there's 20 or 30% left." But the problem is that the JVM (since 1.5, so in
> CF 8, 9, and 10 which are on 1.6) may wait to do a full GC (if it's busy)
> until as much as 95% of memory is used. As such, you may get alerts when you
> set it to 80%, just to have the JVM shortly do a GC and recover.

> Indeed, that could technically be happening to you, Chris. I've seen it
> sometimes wait to 98% full before doing a full GC. That could then be why,
> by the time you look, it's recovered. Really nothing much we can do about
> this. (I mean, sure, there are some JVM tweaks one may consider.) I'd say
> that as long as it DOES recover memory on a GC, that's good news. :-) And if
> it doesn't, you have bigger problems than this alerting mechanism. I will
> note that it's one reason I don't myself use the Memory alert that much.
> Instead, I figure if there's a memory problem, the user will get an
> outofmemory error and can attack it then. Not much else to do with an alert
> in that case until the real problem is solved.

> (To that end, I do wish FR had a 2-stage memory alert, where at stage 1, it
> would do a GC if free memory falls below a given level---such as 20%--and
> then if after a minute, it did not recover to now be below a higher
> level--such as 30%--then it would send alert. That way, you don't get
> notified if the GC solved things. But you do get the GC and an alert if
> things really are starting to go bad, because memory cannot be GCed.)

> More than you sought in your question, Chris, but thought it may help some
> readers.

> /charlie

>> -----Original Message-----
>> From: fusionreactor@googlegroups.com
>> [mailto:fusionreactor@googlegroups.com] On Behalf Of Chris
>> Sent: Tuesday, July 03, 2012 11:47 AM
>> To: fusionreactor@googlegroups.com
>> Subject: [fusionreactor] alert memory different from monitoring memory

>> Hi, I have Crash Protection configured to email alerts when memory
> available
>> gets below 5%. However, many times the alert comes but the current memory
>> usage displayed is completely different.

>> Alert - 97% memory used
>> Monitoring (Request History) - 56% memory used

>> Is the because the JVM is GC'ing quickly and getting memory back ...
>> so the alert triggered because the memory reached that point only for a
> moment?

>> thanks,
>> Chris

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