reading the package db is slow

With a large number of registered packages it takes ages for ghc to read the package db and it does this every time it is run so it starts to add up.

I have a rather fast x86-64 machine and 160 registered packages. Here are some timings:

$ time ghc-pkg list > /dev/null
user    0m1.164s

$ time ghc -c does-not-exist.c 2> /dev/null
real    0m0.612s

$ time hsc2hs does-exist.hsc --cflag=--version 2> /dev/null
user    0m0.572s

So since cabal configure involves running all of the above it starts to take a while:

$ time cabal configure
Configuring cabal-install-0.4.3...
real    0m2.241s
user    0m1.916s

The obvious solution is to use a binary cache of the package db containing the most commonly needed mappings like module name -> package etc.

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Driver
Test case
Differential revisions
BlockedBy
Related
Blocking
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Operating system	Multiple
Architecture