CODEWITHSUNDEEP
scalascala-2.10
Mike
Mike

Reputation: 1849

Scala 2.10 compiler takes 10x longer after first time in SBT

I'm updating some code from 2.9.1 to 2.10.0 (and I tried 2.10.1 with the same results), using SBT 0.12.1 in both cases.

When I run sbt clean compile on the command line, they both complete after about 250 seconds.

However, when I run sbt interactively, and repeatedly enter clean then compile, my 2.9 compiles get faster, but my 2.10 compiles get 10x slower.

If I use a heap size of 768m, 2.10 runs out of memory on the 3rd compile. With a heap size of 4g, it's able to compile each time, but always 10x slower after the first iteration.

[success] Total time: 258 s, completed Mar 14, 2013 10:44:34 AM
[success] Total time: 2048 s, completed Mar 14, 2013 11:23:03 AM
[success] Total time: 2049 s, completed Mar 14, 2013 11:58:42 AM
[success] Total time: 2047 s, completed Mar 14, 2013 12:43:19 PM

What is the best way for me to debug to find out what's going on?

Upvotes: 8

Views: 1374

Answers (2)

Mike
Mike

Reputation: 1849

Thank you retronym for the CodeCache link. I initially dismissed it, since using its suggested -XX:+UseCodeCacheFlushing option made no improvements, but I just tried using -XX:ReservedCodeCacheSize=2g and that solved the problem.

Does anyone know why -XX:+UseCodeCacheFlushing doesn't help, or some recommended values for all of the code cache java options?

For fun, here are my resulting compile times using -XX:+HeapDumpOnOutOfMemoryError -server -XX:ReservedCodeCacheSize=2g -Xmx4g -Xss4M -XX:MaxPermSize=512M -XX:+DoEscapeAnalysis -XX:+UseCompressedOops -XX:+CMSClassUnloadingEnabled -XX:+UseCodeCacheFlushing

2.10.1 (interactive, repeating clean/compile)
    194 s
    149 s
    95 s
    87 s
    84 s
2.9.1 (interactive, repeating clean/compile)
    187 s
    129 s
    83 s
    77 s
    74 s
2.10.1 (batch sbt clean compile)
    195 s
2.9.1 (batch sbt clean compile)
    177 s

Upvotes: 7

Randall Schulz
Randall Schulz

Reputation: 26486

You might start by attaching a profiler or monitor to see what's going on with GC. To get some initial idea of what's up a stock tool like JVisualVM should suffice. Of course, if you have YourKit, that would work well, too.

Addenddum

As a mildly interesting but now largely irrelevant aside, I recently discovered that Scala 2.9.0-1 was atrociously slow when compiling Specs2 tests (immutable, at least). Switching to 2.9.1 made a huge difference. I only noticed it when I had to add some unit tests to a project that had not previously had any and the compile times became agonizing. On a hunch I switched to 2.9.1 and everything went back to normal.

Upvotes: 0

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