monitoring GC

[Annekee Dufour]

I have some applications running with java 1.4.2, and use all kinds of fashionable garbage collection monitoring options there.
But now I have this other application that really needs jdk 1.3.1, and all I can find is verbose:gc. It shows how much time the garbage collection takes and how much garbage gets collected, but it does not even give me a timestamp. There must be more! Anyone?

[Jeffrey Spaulding]

Hi
i don't know if this one
-Xloggc:/whereyoustoreyour/logs/gc.log
already exists in 1.3.x,
in 1.4.x it gives you something like

  
--------------------------------------------------------
19890.325: [GC 13699K->7894K(64832K), 0.0078300 secs]
19904.722: [GC 13718K->8030K(64832K), 0.0104100 secs]
--------------------------------------------------------

Bye,
J.

[Annekee Dufour]

It doesn't exist, that's my problem!

[Billybob Marshall]

Why in the world should your app care WHEN garbage collection occurs, or how frequently, or how much it collects at a time, etc etc etc? This should not be an application requirement.

[Ernest Friedman-Hill]

You could pipe the log through another process that added a timestamp to each line; here's one in Perl (don't laugh, I'm not much of a Perl hacker

#!/usr/bin/perl
require "ctime.pl";
while (<> :wink:  {
  $the_time = &ctime(time);
  chomp $the_time;
  print $the_time, ": ", $_ ;
}

This reads standard input and prints every line it reads preceded by a POSIX date string.

[Annekee Dufour]

Thanx Ernest.
BillyBob, I sometimes see full GCs that take 7 seconds. This is harming my response times (which need to be below 2 seconds). I want to see how often that occurs. I also want to know the percentage of time my system spends garbage collecting. Maybe some tuning is necessary, increase memory or change how it is divided between young space, eden etc, another kind of garbage collection.