#15938: Hadrian's recompilation check is extremely slow -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.8.1 Component: Build System | Version: 8.6.2 (Hadrian) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by NeilMitchell): If you are spending all the time in file pattern matching, I'd say that's a strong suggestion you are doing a lot more file pattern matching that is desirable. Yes, it could be faster, but in a normal build system I'd expect it to be in the weeds - less than 1%. The real culprit though is almost certainly TypeMap.unionWith, which corresponds to adding a user rule during startup (e.g. with %>). In a normal build system I'd expect perhaps 100 user rules. If you want to match on a million rules you have, you put them in a dictionary yourself and add a predicate rule. My guess is Hadrian probably has a list and unrolls it into Shake one at a time. Once you have a huge number of user rules, and match on each linearly, you become quadratic in a huge number. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15938#comment:23 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler