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[AppMon] Server Memory Management

james_mackin
Inactive

We just had a low memory alert on our dAppMon server. We currently run it with -Xms16G and -Xmx16G (and use about 13-14G or so, based on the monitoring dashboard). Our MaxPermSize was 256M.

 

The alert said "Memory Pool 'Code Cache' low memory detected: 95% of 48Mb used". Description: Low PermGen memory will lead to server crashes even if enough heap memory is available.

 

Could someone help explain what the 48Mb number comes from, and what issues we will run into increasing the MaxPermGen size up to 384M? I am now getting a server alert that says that this number isn't in the recommended AppMon guidelines, but we run JVMs in house with MaxPermGen up to 500M and above.

5 REPLIES 5

andreas_grabner
Dynatrace Leader
Dynatrace Leader

Hi James



We are looking into this. The alert message might be misleading here. Will come back to you with an answer on this.



Andi

stefan_frandl
Newcomer

Hi James,



the default maximum CodeCache size for a server VM (-server) is 48 MB. You could prevent running in a problem with the code cache by increasing the maximum CodeCache size:



  • -XX:ReservedCodeCacheSize=64m




Just for explanation - the Permanent Generation and the CodeCache are both non-heap spaces. The PermSize does not include the CodeCache but is a separate non-heap pool.



Stefan

james_mackin
Inactive

Thanks. We increased the ReservedCodeCacheSize to 64m, and dropped the maxpermgen size back down to 256, to avoid the warnings.

service_apms
Organizer

Hi @Stephan and @James,

we had the same probleme "Memory Pool 'Code Cache' low memory detected: 95% of 48Mb used" but i don't know where to increase the codeCache size !!! any help please.

Walid

Hi

add the following line in dtserver.ini

-XX:ReservedCodeCacheSize=64M

Flo