Commit processing slowing down as more commits are processed

[asharov]

It appears that, as the repository processing proceeds, later commits take more time to process than earlier commits. This leads to very large processing times on large repositories. This needs to be investigated and fixed.

Two things to check before making any changes:

1. Is the effect real? Commit processing time should depend only on the size of the commit. Verify first that the increased time required by later commits is not only caused by the later commits being more complex.
2. Where is the increase? What is causing a later commit to take more time than an earlier commit? Is it internal data structures, git, database, ...?