Why does Java code slow down in debugger?

java debugging jboss intellij-idea
Marcus Leon picture Marcus Leon · Feb 3, 2010 · Viewed 12.2k times · Source

Some CPU intensive routines get dramatically slower when run through a debugger. Why is this?

Currently I'm just using IntelliJ to step through code running in JBoss. When I start JBoss, I use these options: 

set JAVA_OPTS=-Xms512m -Xmx1024m -XX:MaxPermSize=256m -Xdebug -Xrunjdwp:transport=dt_socket,address=5005,server=y,suspend=n %JAVA_OPTS%

Is there a way to speed up the execution? Or to speed up certain method executions that I don't need to step through?

Update: Seems if I don't step over/into the CPU intensive routines (ie: Just run til a breakpoint set right after the routine), then the execution time is as if not in a debugger.

Answer

Anon. picture Anon. · Feb 3, 2010

Some CPU intensive routines get dramatically slower when run through a debugger. Why is this?

Because the JITter won't optimize code as much (often, not at all) when debugging is enabled.

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