1) [Full GC 34521K->15504K(38328K), 0.5953540 secs] [GC 27533K->16335K(38328K), 0.0396336 secs]
2) what does the above statements got in catalina.out means, is garbage collection active?
Yes, garbale collection is active. When the garbage collector runs, it will print a line out to stdout (or stderr?) which ends up in your catalina.out.
If it runs a 'full' GC (where it takes a lot of time and cleans up a lot of stuff), then it'll say "Full GC", like the first example. Otherwise, it's doing an incremental GC and not hitting everything, like the second example. In a healthy syste, you should see lots of regular GCs, and occationally see a full GC.
The two big numbers indicate the size of the active heap (the total size of 'live' objects before and after the GC). So, in the first one, the heap was reduced from 34521k of active objects to 15505k of active objects. The number in parens () is the size of the non-permanent heap, which is the total heap minus one of the surviver spaces.
The last number is the wall-clock time that the GC was active -- it tools half a second to so a full GC and about 1/20 of a second to do the incremental GC.
Please see http://java.sun.com/docs/hotspot/gc1.4.2/#2.2.%20Measurement|outline for more information.
When i execute top command on solaris and see the memory it shows size and resisdent memory , what is the diference between the two.
I think this might mean different things to different OSs, but generally the "size" is the total size of executable + code + heap for that process -- everything it needs to run. The 'resident' is usually the amount of 'size' that's actually in physical RAM and not swapped out to disk by the OS.
3) I see that gc statements are logged to catalina.out but the memory usage keeps increasing, does it mean there is problem with garbage collection,
When you say 'memory usage', do you mean from top? Right. Java doesn't return memory to the OS once it requests it -- there's generally no need to do that. Even though Java's heap has more 'space' left over in it, it only has space left over for more Java objects. You should not be comparing the Java heap and GCs to what you read out of 'top'. You should use Runtime.freeMemory (the available heap size), Runtime.totalMemory (the total heap size + internal VM memory), and Runtime.maxMemory (the maximum amount of memory that the VM will try to use).
4) can we get more information like how many obejcts created / objects destroyed during a gc run, what options to pass to get that information
You need a profiler to do heap inspections, which has been discussed many times on this list. I'm not sure you can find out exactly what the GC is doing... you might need a very nice profiler for that.
-chris
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