If the /var/lib/apk/world file grows bigger than 1023 bytes it gets corrupt.

in vim it might look like this:
… renderproto resou^�&`~^E

After that apk will complain:
ERROR: No providers for ‘resou’
ERROR: Failed to build installation graph

You can workaround things from there by deleting resou:
$ sudo apk del resou
Purging resourceproto (1.0.2-r0)
OK: 133 packages, 4458 dirs, 67648 files

(from redmine: issue id 8, created on 2009-03-17, closed on 2009-03-17)

• Changesets:
  • Revision 7735cc64 by Timo Teräs on 2009-03-17T11:19:06Z:

pkg: write dependencies directly file instead of buffer

So we don't get artificial limits on the amount of dependencies
(fixes #8).