parsers: incrementally parse the revlog index in C We only parse entries in a revlog index file when they are actually needed, and cache them when first requested. This makes a huge difference to performance on large revlogs when accessing the tip revision or performing a handful of numeric lookups (very common cases). For instance, "hg --time tip --template {node}" on a tree with 300,000 revs takes 0.15 before, 0.02 after. Even for revlog-intensive operations (e.g. running "hg log" to completion), the lazy approach is about 1% faster than the eager parse_index2.