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Scala 2.9 Compiler Performance
We have migrated a few projects to Scala 2.9, and have measured an
increase in compilation time. It's something of a pain point.
We are using SBT 0.7.7 and Scala 184.108.40.206.
The total compile time for one project increased from 146s to 307s. I
have published the statistics, gathered with -Ystatistics, for one
module . Time spent in implicits during type checking has
It's not a perfectly scientific test, as some dependencies (Akka,
Scalaz, SQLRL) were updated during the migration. We are working on a
more isolated test.
As another data point, the Scala build (including tests) is also
slower with 2.9. 
There were quite a few changes, some performance related, in
Implicits.scala  for 2.9.
Could others share there experience with compiler performance after
the 2.9 upgrade? If you find a big difference, could you post the
output of scalac -Ystatistics for 2.8.1/220.127.116.11?
We do plan to migrate to SBT 0.10 to avoid needless recompilation, but
obviously the clean build performance is still important.