Summary:
Commit messages and extras can be unbounded in size. This can cause problems if users create commits with exceptionally large messages or extras. Mercurial will commit these to the changelog, increasing its size. On Mononoke, large commit messages may go over the cacheing threshold, resulting in poor performance for requests involving these commits as Mononoke will need to reload on every access.
Commit messages should not usually be that large. Mostly likely it will happen by accident, e.g. through use of `hg commit -l some-large-file`. Prevent this from happening by accident by adding configuration for soft limits when creating commits.
If a user really does need to create a commit with a very large message or extras, they can override using the config option.
Reviewed By: xavierd
Differential Revision: D19942522
fbshipit-source-id: 09b9fe1f470467237acc1b20286d2b1d2ab25613
