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Comments on Virtualization

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Onno Molenkamp said ...

The VIRT column doesn't say much about the amount of memory used. This can be easily seen by comparing the total amounts of memory used in both cases: they're more or less the same, even though the VIRT value for the java process is very different.

--Onno Molenkamp 18:07, 14 June 2010 (CEST)

Well, that was my assumption as well. But for some reason it is not true. Starting many (maybe only Java) processes with huge VIRT size, just kills the system, forcing it to use huge amount of swap.

--JaroslavTulach 11:11, 15 June 2010 (UTC)

Nathan said ...

This isn't just a virtualization issue - I upgraded my PC to Ubuntu 10.04 which uninstalled the Sun JDK and installed OpenJDK. Any development work I did in Netbeans which launched Glassfish completely crippled my machine. After removing OpenJDK and re-installing the Sun JDK, all was well again. This on a straight Linux machine, no virtualized anything. Given this, I cannot honestly recommend OpenJDK for any purpose what-so-ever.

Added on top of this is that the OpenJDK applet plugin doesn't support the Java console, so debugging applets is infeasible (there's a work-around to launch FireFox from a console, but that's not helpful when trying to debug for an end-user).

--Nathan 02:26, 15 June 2010 (CEST)

I'll do my best to make sure this testimony is seen by OpenJDK guys. --JaroslavTulach 11:11, 15 June 2010 (UTC)

Daniel said ...

I agree that 512m is much too high for most Java applications. A recent version of Sun JDK bumped the default heap size to 256 MB, though, so if you're concerned about resources, I'd strongly recommend to find a way for setting the maximum heap and permgen size in Hudson (I guess it'd be fine with 64 MB too).

--Daniel 09:20, 15 June 2010 (CEST)

256MB!? Hopefully they at least check whether the system has 256MB of real memory! If not, I at least know where to report a bug. --JaroslavTulach 11:11, 15 June 2010 (UTC)

Antony John said ...

I faced the same problem with OpenJdk 1.6 in 10.4 Ubuntu and reverted to sun jdk 1.6.. and reduced the default heap allocations.. My machine even after having 2 GB of memory + flash based parallel swap went into grinding halts.. I think any app using more than 64 MB on startup is bloat-ware... Thanks Nathan for pointing out.. By the way I switched to Netbeans and they have this wonderful activation on demand mechanism for plugins that helps to manage memory more efficiently..

--Antony John 20:12, 15 June 2010 (CEST)

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