Spring Web应用程序内存配置文件怀疑

Question

I have Spring application with top command showing following data on Amazon EC2 small instance ( 1.7 GB RAM ) -

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                  
 5019 ubuntu    20   0 1971m 446m  17m S  4.7 27.0  31:25.61 java    

This is taking 446 MB of memory only for booting software and I have about 350 classes and there are libraries brought in as dependencies by Maven.

free -m 

             total       used       free     shared    buffers     cached
Mem:          1656       1642         14          0         34        519
-/+ buffers/cache:       1088        568
Swap:          895         12        883

Maven Spring dependencies are there -

Spring Core, Spring MVC, Spring Data , Spring Data Rest, , Spring
Security, Spring HATEOAS, Spring Boot, Spring Oauth , Spring-Vaadin

I was comparing this memory footprint to jenkins that is taking 277 MB in total but my test application apparently takes +400 MB without running anything significantly.

At this point code has only Entities and Spring Data Rest. I did a heap dump analysis and it shows that hibernate took 15 MB for PID as top consumer from application ( taken using jmap )

Used heap dump  76.9 MB
Number of objects   1,785,039
Number of classes   12,546
Number of class loaders 245
Number of GC roots  2,589
Format  hprof

Biggest Top-Level Dominator Class Loaders report in MAT shows -

org.eclipse.jetty.webapp.WebAppClassLoader @ 0xf00f8bb0  - 45 MB - 56.91%

1. Does Spring web applications in general take +400 MB for just starting up when above libraries are added as dependency and run using mvn jetty:run ?
2. Here heap occupancy is shown as 77 MB by jmap though top command shows +400 MB , why they don't match as they both are for same PID 5019

Answer 1

1. It's hard to estimate based on the libraries alone as it depends on your jvm settings, what do you do with your application, did your bootstrap related code used memory efficiently etc? 400mb sounds pretty normal for an app with those dependencies.

2. Heap occupancy is just the portion of memory used by your code and libraries. jvm needs memory too to run. Plus your OS might have its own intricacies when allocating memory.

You can try adjusting various jvm heap memory settings (see http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html ). Some pretty common settings are -Xmx -Xms -XX:MaxPermSize.

My recommendation is use some jvm profiling tool that gives you a heap usage graph (eg: visualvm), make sure the heap consumption doesn't climbs up (look for a sawtooth pattern), and then you can gauge how much you need and adjust the VM parameter .