RFR (M) JDK-6479360 - detailed dumping of class size statistics

Ioi Lam ioi.lam at oracle.com
Wed Jan 16 16:39:52 PST 2013

Please review:

Bug: RFE: PrintClassHistogram improvements

Sponsor: Karen Kinnear


A new diagnostic command "jcmd GC.class_stats" is added. The user
can invoke this command to connect to a live JVM and dump a detailed
report of size statistics of all loaded classes (including array
classes and anonymous classes).

     $ jcmd $PID help GC.class_stats
     Provide statistics about Java class meta data.
     Impact: High: Depends on Java heap size and content.

     Syntax : GC.class_stats [options] [<columns>]

	columns : [optional] Comma-separated list of all the columns to
                   show. If not specified, the following columns are shown:
                   MethodAll,ROAll,RWAll,Total (STRING, no default value)

     Options: (options must be specified using the <key> or <key>=<value> syntax)
	-all : [optional] Show all columns (BOOLEAN, false)
	-csv : [optional] Print in CSV (comma-separated values) format for
                 spreadsheets (BOOLEAN, false)
	-help : [optional] Show meaning of all the columns (BOOLEAN, false)

By default, the output is human-readable tabulated text format. The
user can also select CSV format (comma-separated values) to be
used with spreadsheets.

A large number of columns are available. By default, a few "summary
columns" (e.g., size of Klass objects, total read-only data, etc)
are printed. The user can also manually select the columns.

Please see the attachments in the bug for sample output, as well as
a listing of all the columns and their meanings:



If this diagnostic command is not used, there should be no
impact to the JVM's execution, except for

    + libjvm.so footprint increase (about 10KB larger on Linux/x64)
    + one additional virtual method in Klass.

This feature is excluded when INCLUDE_SERVICES=0 (e.g.,
embedded builds).

Tests run:

+ JPRT -- (hotspot only) to verify build-ability

+ Manually ran "jcmd $PID help GC.class_stats" on Linux/x64

+ I intend to add a new testcase once this is committed:
   Add utility classes for writing better multiprocess tests in jtreg


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