sidedatacopies: only store an entry if it has values...
sidedatacopies: only store an entry if it has values
This will make for a shorter storage and help use to write faster code in simple
case. This change already provided a speed boost for copy tracing.
For example here is combined time of running copies tracing on a 6989 pairs of
revision on the pypy repos:
before: 771s
after: 631s - 18%
This also has a very positive impact on changelog size. For example here are the
number for the `00changelog.d` file of pypy.
before: 30449712 Bytes
after: 24973718 Bytes - 18%
This give an overall quite acceptable overhead for storing copies into the
changelog:
filelog-only: 23370586
sidedata: 24973718 Bytes + 7%
Differential Revision:
https://phab.mercurial-scm.org/D7068
