Heap Size and Stuttering

[vividweb]

I have been reading some recent discussions around increasing java heap size in order to make sage run a little better, so I increased my heap size to 512 and have experienced some strange results.

I have a four tuner system, one PVR-500 and two Network encoders that use DVBDream. I have 4 clients, two MVP's, one HD-100 and one PC. Sage runs as a service on its own server box. My PC client is a little under powered for HD but it would get by.

My strange results for increasing the java heap have affected my PC client. Previously when watching an HD hockey game (broadcast at 1080i) I would experience a slow degradation of the playback, it would slowly change from being flawless to being unwatchable because of stuttering and skipping. I attributed this to my client being underpowered even though my CPU was not maxed out and hadn't changed.

After changing the heap size I am able to watch the exact same HD broadcasts stutter free for whole game. It baffles me how the heap size on the server could boost up a client so much.

With so many people now running multiple tuner, multiple HD client systems does Sage need to increase the default value for the Heap size?

[stuckless]

More memory means less need to garbage collect. I suspect that your stuttering is happening when the java system is having to run the garbarge collector to free up memory.

On a single core machine, depending on the gargbage collection settings, the garbarge collector will interrupt the execution of the program to collect memory. These pauses are relative quick because Java doesn't free ALL memory on each pass. It basically uses a sweeping approach where it will attempt to free the "easy" to access memory first. But if this happens enough, then it will result in short pauses to the system.

On a multi-core machine and a recent jvm, you an have the garbage collector running in a separate thread. This can result in better garbarge collection without the "pausing" effect.

Since java uses a garbage collection model, then each new version of java comes with various tweaks to better help the garbarge collection performance. Prior to 1.4, garbarge collection was very bad.

Another thing to consider is that if you are running a server, then why not give java most of the memory for that system. If it's just going to sit around doing nothing, then you might as well give it to java

[jerryt]

Originally Posted by vividweb

I have been reading some recent discussions around increasing java heap size in order to make sage run a little better, so I increased my heap size to 512 and have experienced some strange results.

I want some of those strange results, How do I change the "Heap Size"?

[vividweb]

The discussion was in the Beta forum.

http://forums.sagetv.com/forums/showthread.php?t=23681

I agree stuckless, if the memory is there why not give to Java to help out, just didn't realize it could be done.

[SpiffyRex]

I agree stuckless, if the memory is there why not give to Java to help out, just didn't realize it could be done.

In most cases it's good to increase the heap to 512, more is not needed. However you need to make sure the OS doesn't start to page too much, XP and Vista need a lot of real memory to run smoothly. Also if you have enough memory you might like to increase the buffer cache (called system cache in windows) for improved I/O.

[stuckless]

Here is tuning guide from Sun.... It's fairly technical, but I've consulted it in the past when I've run into gc issues on other projects. GC Tuning Guide