How Can I monitoring java heap with jstat?

[erasmomarciano]

I'd like to know the heap memory usage with jstat as in jmx.console

exmaple

Heap size 4G

Heap memory usage 3,75G

[wdfink]

jstat is a console tool to monitor the JVM heap and GC.

See the documentation

I often use 'jstat -gc PID <intervall>'

[rhusar]

You may want to use jmap. Here is an example that I like to use:

[rhusar@rhusar as-master]$ jps -l
18374 org.jetbrains.idea.maven.server.RemoteMavenServer
18281 com.intellij.idea.Main
21105 sun.tools.jps.Jps
[rhusar@rhusar as-master]$ jmap -histo:live 18281 | head

 num     #instances         #bytes  class name
----------------------------------------------
   1:        176916       24493688  <constMethodKlass>
   2:        176916       24077408  <methodKlass>
   3:         22170       23879160  <constantPoolKlass>
   4:         22170       18736416  <instanceKlassKlass>
   5:        139987       13574248  [C
   6:        198198       12992576  [B
   7:         18624       12898400  <constantPoolCacheKlass>

Otherwise jconsole is great if you want UI.

[erasmomarciano]

Hi thanks for reply

I know jconsole and other strument for calcolate the sum Heap.

I usally i run kill -3 on the PID

[rhusar@rhusar as-master]$ jmap -histo:live 18281 | head

num     #instances         #bytes  class name
----------------------------------------------
   1:        176916       24493688  <constMethodKlass>
   2:        176916       24077408  <methodKlass>
   3:         22170       23879160  <constantPoolKlass>
   4:         22170       18736416  <instanceKlassKlass>
   5:        139987       13574248  [C
   6:        198198       12992576  [B
   7:         18624       12898400  <constantPoolCacheKlass>

For calculate the sum Heap i have additional the point 1 2 ..7 ? 

I have a result in byte

thank

[rhusar]

AFAIK yes, summing up all the bytes should give you the total heap as well (obviously, dont paste it through head command then as I did in the example above).

jstat will tell you the totals in each generation, which is very useful but if you want to quickly see which objects are holding up the memory jmap comes in handy.

[nikhilmone]

You can also try below command that gives you detail of entire memory usage :

=========================================

$ jmap -heap <Proces ID of your JVM>

Attaching to process ID 29696, please wait...

Debugger attached successfully.

Server compiler detected.

JVM version is 20.6-b01

using thread-local object allocation.

Parallel GC with 4 thread(s)

Heap Configuration:

   MinHeapFreeRatio = 40

   MaxHeapFreeRatio = 70

   MaxHeapSize      = 1367343104 (1304.0MB)

   NewSize          = 1310720 (1.25MB)

   MaxNewSize       = 17592186044415 MB

   OldSize          = 5439488 (5.1875MB)

   NewRatio         = 2

   SurvivorRatio    = 8

   PermSize         = 21757952 (20.75MB)

   MaxPermSize      = 268435456 (256.0MB)

Heap Usage:

PS Young Generation

Eden Space:

   capacity = 341966848 (326.125MB)

   used     = 298634744 (284.80028533935547MB)

   free     = 43332104 (41.32471466064453MB)

   87.32856583805457% used

From Space:

   capacity = 56885248 (54.25MB)

   used     = 56854136 (54.22032928466797MB)

   free     = 31112 (0.02967071533203125MB)

   99.94530743717598% used

To Space:

   capacity = 56885248 (54.25MB)

   used     = 0 (0.0MB)

   free     = 56885248 (54.25MB)

   0.0% used

PS Old Generation

   capacity = 910884864 (868.6875MB)

   used     = 71342136 (68.03716278076172MB)

   free     = 839542728 (800.6503372192383MB)

   7.832179325794572% used

PS Perm Generation

   capacity = 71303168 (68.0MB)

   used     = 71145280 (67.84942626953125MB)

   free     = 157888 (0.15057373046875MB)

   99.77856804342831% used

=========================================