Full GC - Sun JVM frequency of run

views:

answers:

Full GC - Sun JVM frequency of run

In JDK 1.5.0.22 : I see that full GC has been run but the old generation and perm gen space is not used completely - question is as per my understanding FGC only runs when old gen or perm gen is full - I am not able to understand why it has run even though usage % is low?.

See output of jstat -gcutil below:

  S0     S1     E      O      P     YGC     YGCT    FGC    FGCT     GCT
 0.00  82.14  51.17  13.78  26.43    219   19.347     1    0.131   19.479

  S0     S1     E      O      P     YGC     YGCT    FGC    FGCT     GCT
 82.14   0.00   9.12  13.92  26.66    222   19.771     1    0.131   19.902

  S0     S1     E      O      P     YGC     YGCT    FGC    FGCT     GCT
 82.14   0.00  11.07   9.07  24.15    230   20.166     2    1.851   22.017

My min/max heap is 1024M and min and max permGen space is defined as 768M.

FGC only runs when old gen or perm gen is full

It's not true. Read this http://java.sun.com/j2se/reference/whitepapers/memorymanagement_whitepaper.pdf

Memory management in Java may surprise everyone. It takes many years to learn how to set JVM parameters for non-trivial applications.

permGen space is defined as 768M.

Decrease it to 128M

iddqd 2010-10-18 08:32:27

Cannot decrease perm gen space - as our application consumes it heavily... are there any disadvantage to using a high value for it?

Anna 2010-10-18 10:44:47

Why does you application consume perm gen heavily ? Do You use dom xml parser or compare many strings an call intern ?

iddqd 2010-10-18 10:53:25

From the pdf link you have quoted: "When the young generation fills up, a young generation collection (sometimes referred to as a minor collection) of just that generation is performed. When the old or permanent generation fills up, what is known as a fullcollection (sometimes referred to as a major collection) is typically done" . What are those cases when the old/perm gen are not full and yet GC is done??.

Anna 2010-10-18 10:55:50

Too many JSP's are loaded - which increases the usage of permgen space...

Anna 2010-10-18 10:58:07

Which app server do You use ?

iddqd 2010-10-18 11:02:01

Apache Tomcat 5.5.9/ jdk 1.5 update 22

Anna 2010-10-18 11:13:27

You have problem with YG not PG or OG. Which collector do you use ? Tomcat in this version is a museum.leaks. First of all decrease PG (it use only 25%) or increase heap.

iddqd 2010-10-19 08:35:46

ansaurus

tags:

views:

answers:

Full GC - Sun JVM frequency of run

related questions