git: cache the number of commits to speed up large repo operations Instead of iterating over the whole changelog table every time we want to know how many commits there are, we can cache the number between mercurial invocations. Unsurprisingly, this speeds up certain operations on repos with large histories. The following measurements are all in seconds and they represent the runtime of `hg log -T ' ' -l1 > /dev/null`. In other words, this includes python startup overhead, etc. On small and medium repos, there is no observable difference in runtime (because of the relatively large overhead of python runtime startup, and the rest of mercurial doing useful work), but on large repos the user-visible execution time drops by a factor of 10x or more. small repo (~600 commits): Min. 1st Qu. Median Mean 3rd Qu. Max. 0.1052 0.1076 0.1096 0.1102 0.1110 0.1210 (before) 0.1049 0.1087 0.1106 0.1120 0.1127 0.1302 (after) medium repo (12k commits): Min. 1st Qu. Median Mean 3rd Qu. Max. 0.1063 0.1095 0.1116 0.1129 0.1153 0.1349 (before) 0.1044 0.1092 0.1108 0.1115 0.1130 0.1326 (after) large repo (1.4M commits): Min. 1st Qu. Median Mean 3rd Qu. Max. 1.973 2.105 2.256 2.243 2.406 2.443 (before) 0.144 0.147 0.148 0.150 0.151 0.176 (after)