jvm load too many classes
mandy.chung at oracle.com
Fri Jul 30 19:59:45 UTC 2010
Osvaldo Doederlein wrote:
> I wonder if these numbers have some variation per platform?
Yes, there are some platform-dependent classes and so some loaded
classes are different on different platform.
> For me (on
> Windows; 32-bit JDKs), the results of this test (java -verbose:class |
> grep Loaded | wc -l) are:
> 1.5.0_22: 239
> 1.6.0_21: 274
> 1.7.0-ea-b103: 403
I ran the helloworld. The number of loaded classes running different jdk
versions are fairly close. What test case did you use?
$ grep Loaded hw.verbose.jdk5u22 | wc -l
$ grep Loaded hw.verbose.jdk6u21 | wc -l
$ grep Loaded hw.verbose.jdk7 | wc -l
> The diff from 1.5 to 1.6 is not bad, but JDK7 seems right now to be a
> heavy regression... FWIW for such a simple test. For one thing, these
> core-boot classes all come off the CDS file so their classloading
> effort is relatively very small, and the delta will certainly be much
> smaller for even the smallest real-world app.
Right. -verbose:class prints out all loaded classes regardless of
coming from CDS archive or not. The number of loaded classes is one
metric to the startup while class loading time + clinit time are
other important metrics. So these loaded classes has small impact
to the startup time especially with CDS is enabled.
> 2010/7/30 Mandy Chung <mandy.chung at oracle.com>:
>> Yongqiang Yang wrote:
>>> I just type command "java" under openjdk1.6, then the jvm will load
>>> 308 classes, including java/launcher/LauncherHelp,
>>> When I use jdk1.5, the jvm just load about 180 classes, not
>>> including the classes above.
>>> Could someone figure out something wrong?
>> New features and bug fixes in a new release could lead to more classes get
>> loaded at startup. We have done some work to lazily load classes if
>> appropriate (see CR 6798873: Reduce the number of classes loaded and class
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