Why does java wait so long to run the garbage collector?

I am building a Java web app, using the Play! Framework . I'm hosting it on playapps.net . I have been puzzling for a while over the provided graphs of memory consumption. Here is a sample:

Heap Memory

The graph comes from a period of consistent but nominal activity. I did nothing to trigger the falloff in memory, so I presume this occurred because the garbage collector ran as it has almost reached its allowable memory consumption.

My questions:

Is it fair for me to assume that my application does not have a memory leak, as it appears that all the memory is correctly reclaimed by the garbage collector when it does run?

(from the title) Why is java waiting until the last possible second to run the garbage collector? I am seeing significant performance degradation as the memory consumption grows to the top fourth of the graph.

If my assertions above are correct, then how can I go about fixing this issue? The other posts I have read on SO seem opposed to calls to System.gc() , ranging from neutral ("it's only a request to run GC, so the JVM may just ignore you") to outright opposed ("code that relies on System.gc() is fundamentally broken"). Or am I off base here, and I should be looking for defects in my own code that is causing this behavior and intermittent performance loss?

I apologize for the brain dump of questions; I've been debugging this issue for a while now, and would greatly appreciate any pointers.

UPDATE

I have opened a discussion on PlayApps.net pointing to this question and mentioning some of the points here; specifically @Affe's comment regarding the settings for a full GC being set very conservatively, and @G_H's comment about settings for the initial and max heap size.

Here's a link to the discussion , though you unfortunately need a playapps account to view it.

I will report the feedback here when I get it; thanks so much everyone for your answers, I've already learned a great deal from them!

Resolution

Playapps support, which is still great, didn't have many suggestions for me, their only thought being that if I was using the cache extensively this may be keeping objects alive longer than need be, but that isn't the case. I still learned a ton (woo hoo!), and I gave @Ryan Amos the green check as I took his suggestion of calling System.gc() every half day, which for now is working fine.

Thanks again for all the help, as always!

Why is this Javascript much slower than its jQuery equivalent?

I have a HTML list of about 500 items and a "filter" box above it. I started by using jQuery to filter the list when I typed a letter (timing code added later): $('#filter').keyup( function() { var jqStart = (new Date).getTime(); var search = $(this).val().toLowerCase(); var $list = $('ul.ablist > li'); $list.each( function() { if ( $(this).text().toLowerCase().indexOf(search) === -1 ) $(this).hide(); else $(this).show(); } ); console.log('Time: ' + ((new Date).getTime() - jqStart)); } ); However, there was a couple of seconds delay after typing each letter (particularly the first letter). So I thought it may be slightly quicker if I used plain Javascript (I read recently that jQuery's each function is particularly slow). Here's my JS equivalent: document.getElementById('filter').addEventListener( 'keyup', function () { var jsStart = (new Date).getTime()...

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