CODEWITHSUNDEEP
javagarbage-collectionjvm
Alexis
Alexis

Reputation: 1152

How to control old generation size of java heap?

I want to controller the old generation size of the java heap. And I have these settings below:

-Xmx1024m -XX:MaxNewSize=640m -XX:NewSize=640m -XX:SurvivorRatio=5 -XX:-UseAdaptiveSizePolicy -XX:PermSize=32m -server

After launch the application, I execute "jmap -heap pid" and it shows:

Attaching to process ID 96921, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.51-b03

using thread-local object allocation.
Parallel GC with 4 thread(s)

Heap Configuration:
   MinHeapFreeRatio = 40
   MaxHeapFreeRatio = 70
   MaxHeapSize      = 1073741824 (1024.0MB)
   NewSize          = 671088640 (640.0MB)
   MaxNewSize       = 671088640 (640.0MB)
   OldSize          = 5439488 (5.1875MB)
   NewRatio         = 2
   SurvivorRatio    = 5
   PermSize         = 33554432 (32.0MB)
   MaxPermSize      = 85983232 (82.0MB)
   G1HeapRegionSize = 0 (0.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 480247808 (458.0MB)
   used     = 81462752 (77.68893432617188MB)
   free     = 398785056 (380.3110656738281MB)
   16.962649416194733% used
From Space:
   capacity = 95420416 (91.0MB)
   used     = 61444600 (58.59813690185547MB)
   free     = 33975816 (32.40186309814453MB)
   64.39355703500601% used
To Space:
   capacity = 95420416 (91.0MB)
   used     = 0 (0.0MB)
   free     = 95420416 (91.0MB)
   0.0% used
PS Old Generation
   capacity = 5767168 (5.5MB)
   used     = 90128 (0.0859527587890625MB)
   free     = 5677040 (5.4140472412109375MB)
   1.5627774325284092% used
PS Perm Generation
   capacity = 35127296 (33.5MB)
   used     = 35092152 (33.46648406982422MB)
   free     = 35144 (0.03351593017578125MB)
   99.89995244723647% used

15721 interned Strings occupying 1939128 bytes.

My problem is why the old size is 5mb, I think it should be 300+mb = MaxHeapSize - NewSize - PermSize = 1024 - 640 - 32

What's wrong with my setting and how can I control the old size?

Upvotes: 2

Views: 5710

Answers (1)

the8472
the8472

Reputation: 43042

You're not setting a minimum heap size, thus allowing the old gen to grow/shrink. Adaptive size policy only affects the new/old gen boundary. Set -Xms1024m.

Considering that you didn't even know that I suspect the selection of your other parameters may be ill-informed. I would recommend setting high-level goals (pause times, throughput, heap free ratios) instead and letting the heuristics do their work.

Recommended reading: Hotspot GC Tuning Guide

Upvotes: 1

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