What is Verbose Garbage Collection (verbosegc) and How do I Enable it on WebLogic

问题描述：

　　What is Verbose Garbage Collection (verbosegc) and How do I Enable it on WebLogic

问题分析：

　　通过添加gc参数解决

解决办法：

Verbose garbage collection (verbosegc) is a Java option you can set, when starting WebLogic, so that all java garbage collection activity is recorded to a WebLogic log. Verbose garbage collection is sometimes enabled for diagnostic purposes, when there are memory-related issues or performance-related issues on the WebLogic server. Although there are many options for java tuning, our developers often request verbosegc to troubleshoot memory issues.

HOW TO ENABLE VERBOSE GARBAGE COLLECTION

To enable verbose garbage collection, do the following:

1. First add the 'Verbose Garbage Collection' option to the java command line. Below are instructions, based on the operating system you are using:

In Linux environments (using PeopleTools 8.53 - 8.57 PeopleTools releases):
a. Edit <PIA_HOME>/webserv/<DOMAIN_NAME>/bin/setEnv.sh
b. Add parameter '-verbose:gc and -XX:+PrintGCDateStamps' to the "JAVA_OPTIONS_LINUX" line .  Example
JAVA_OPTIONS_LINUX="-Xms2048m  -Xmx2048m -verbose:gc -XX:+PrintGCDateStamps -Dtoplink....

In Solaris environments (using PeopleTools 8.56 or lower PeopleTools release):
a. Edit <PS_HOME>/webserv/<DOMAIN_NAME>/bin/setEnv.sh
b. Add parameters ' -XX:+PrintGCDateStamps -verbosegc' to the "JAVA_OPTIONS_OS" line .
For example:
   JAVA_OPTIONS_SOLARIS="-server -Xms2048m -Xmx2048m -XX:MaxpermSize=128m  -XX:+PrintGCDateStamps -verbosegc -Dtoplink....

In HP and AIX enviroments:
a. Edit <PS_HOME>/webserv/<DOMAIN_NAME>/bin/setEnv.sh
b. Add parameter '-verbose:gc -XX:+PrintGCTimeStamps' to the "JAVA_OPTIONS_OS" line .
For example, if web server is on AIX, the following change would be made:
   JAVA_OPTIONS_AIX="-server -Xms512m -Xmx512m -verbose:gc -XX:+PrintGCTimeStamps -Dtoplink....
For HP:
   JAVA_OPTIONS_HPUX="-server -Xms2048m -Xmx2048m -verbose:gc -XX:+PrintGCTimeStamps -Dtoplink....

In Windows environment where WebLogic is started as a Windows service, update the Windows registry as follows:
a. Choose start-run-regedit
b. From regedit, go to [HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\peoplesoft-PIA, or whatever your service name is.
c. Highlight that service and expand
d. Click 'Parameters'
e. Double-click on cmdline.
f.  If Using JRockit (ie PeopleTools 8.50 to 8.52), then add '-Xverbose:gc -Xverbosetimestamp' after the heap settings.
    Example:
        -server -Xms2048m -Xmx2048m -Xverbose:gc -Xverbosetimestamp ......
    If Using Sun Java (PeopleTools 8.49 or older and 8.53 and higher), then add '-verbosegc' after parameter MaxPermSize.
    Example:
        -server -Xms256m -Xmx2048m -XX:MaxPermSize=2048m -verbosegc ......

In Windows environment, where WebLogic is started in foreground, add the verbose gc parameters (outlined above)  to line JAVA_OPTIONS_WINxx in setEnv.cmd.

NOTE: You can redirect the Garbage Collection output to a separate file by using the parameter -Xloggc. For example on Windows add -Xloggc:c:\temp\gc.log

2. Restart the web server in order to pick up the change

3. The verbose garbage collection will be logged to the following file: 
a. If using Linux, file is <PS_CFG>/webserv/<DOMAIN_NAME>/servers/PIA/logs/PIA_stderr.log 
b. If using Windows service, file is   <PS_CFG>/webserv/<DOMAIN_NAME>/servers/PIA/NTservice-<DOMAIN-NAME>-PIA.log
c. If using IBM, file is <PS_CFG>/webserv/<DOMAIN_NAME>/servers/PIA/PIA_stderr.log
d. For all other platforms, the verbose garbage collection is usually logged to <PS_CFG>/webserv/<DOMAIN_NAME>/servers/PIA/logs/PIA_stdout.log

HOW TO ANALYZE VERBOSE GARBAGE COLLECTION LOGS
======================================================
When analyzing verbose garbage collection we often concentrate on the full garbage collections (vs minor collections). Points of interest are:
    a) How often is full garbage collection taking place?
    b) How long is garbage collection taking? Full garbage collection should not take longer than 3 to 5 seconds.
    c) What is your average memory footprint? In other words, what does the heap settle back down to after each full garbage collection?

Note that depending on the type and version of Java you are using (JRockit, IBM, HP or Sun), the format for a full GC varies.   Below are a couple examples:

EXAMPLE 1:
-----------------
Below is an example of a log entry, for a full GC in a WebLogic environment using JRockit R28:

46.587-46.829: OC 505693KB->395689KB (4194304KB), 0.243 s, sum of pauses 204.262 ms, longest pause 204.262 ms.

The format, for the above example is:

<start>-<end>: <type> <before>KB-><after>KB (<heap>KB), <time> ms, sum of pauses <pause> ms

In the above example, the type 'OC' stands for 'Old Collection', which is the same as a full Garbage collection ('YC' or 'Young Collection' is the type used for a minor GC). In this example, heap usage before GC was 505.7 meg. After the GC, the heap usage was 395.7 meg.   The heap is set to a max of 4 gb.  It took 204 milliseconds to perform the garbage collection.

EXAMPLE 2:
-----------------
Below is an example of a log entry, for a full GC in a WebLogic environment using Sun Java:

[Full GC 28053K->28022K(255104K), 0.3735740 secs][Mon Nov 24 11:42:56 2008]

The format is

[GC<before>K-><after>K(<heap>K)<total>secs]

In above example, usage before GC was 28053K and 28022K after the GC. The heap size is set to 255104K. It took .37 seconds for the GC.

EXAMPLE 3:
--------------------
For IBM, the verbose GC information is normally in xml format.  Example:

<af type="tenured" id="1" timestamp="Aug 13 16:19:36 2013" intervalms="0.000">
  <minimum requested_bytes="272" />
  <time exclusiveaccessms="0.916" meanexclusiveaccessms="0.470" threads="2" lastthreadtid="0x0000000031C39700" />
  <refs soft="12698" weak="8843" phantom="32" dynamicSoftReferenceThreshold="29" maxSoftReferenceThreshold="32" />
  <tenured freebytes="53686272" totalbytes="1073741824" percent="4" >
    <soa freebytes="0" totalbytes="1020055552" percent="0" />
    <loa freebytes="53686272" totalbytes="53686272" percent="100" />
  </tenured>
  <gc type="global" id="2" totalid="2" intervalms="65208.114">
    <classunloading classloaders="48" classes="0" timevmquiescems="0.000" timetakenms="7.874" />
    <finalization objectsqueued="9836" />
    <timesms mark="188.929" sweep="8.768" compact="0.000" total="206.155" />
    <tenured freebytes="920823288" totalbytes="1073741824" percent="85" >
      <soa freebytes="867137016" totalbytes="1020055552" percent="85" />
      <loa freebytes="53686272" totalbytes="53686272" percent="100" />
    </tenured>
  </gc>

Note that the attributes of most interest are the "tenured freebytes" (after the "af" section and after the "gc" section) as this shows you heap size before and after the garbage collection.