util: reword debugstacktrace comment

changelog: avoid slicing raw data until needed Before, we were slicing the original raw text and storing individual variables with values corresponding to each field. This is avoidable overhead. With this patch, we store the offsets of the fields at construction time and perform the slice when a property is accessed. This appears to show a very marginal performance win on its own and the gains are so small as to not be worth reporting. However, this patch marks the end of our parsing refactor, so it is worth reporting the gains from the entire series: author(mpm) 0.896565 0.795987 89% desc(bug) 0.887169 0.803438 90% date(2015) 0.878797 0.773961 88% extra(rebase_source) 0.865446 0.761603 88% author(mpm) or author(greg) 1.801832 1.576025 87% author(mpm) or desc(bug) 1.812438 1.593335 88% date(2015) or branch(default) 0.968276 0.875270 90% author(mpm) or desc(bug) or date(2015) or extra(rebase_source) 3.656193 3.183104 87% Pretty consistent speed-up across the board for any revset accessing changelog revision data. Not bad! It's also worth noting that PyPy appears to experience a similar to marginally greater speed-up as well! According to statprof, revsets accessing changelog revision data are now clearly dominated by zlib decompression (16-17% of execution time). Surprisingly, it appears the most expensive part of revision parsing are the various text.index() calls to search for newlines! These appear to cumulatively add up to 5+% of execution time. I reckon implementing the parsing in C would make things marginally faster. If accessing larger strings (such as the commit message), encoding.tolocal() is the most expensive procedure outside of decompression.

changelog: parse description last Before, we first searched for the double newline as the first step in the parse then moved to the front of the string and worked our way to the back again. This made sense when we were splitting the raw text on the double newline. But in our new newline scanning based approach, this feels awkward. This patch updates the parsing logic to parse the text linearly and deal with the description field last. Because we're avoiding an extra string scan, revsets appear to demonstrate a very slight performance win. But the percentage change is marginal, so the numbers aren't worth reporting.

changelog: lazily parse files More of the same. Again, modest revset performance wins: author(mpm) 0.896565 0.822961 0.805156 desc(bug) 0.887169 0.847054 0.798101 date(2015) 0.878797 0.811613 0.786689 extra(rebase_source) 0.865446 0.797756 0.777408 author(mpm) or author(greg) 1.801832 1.668172 1.626547 author(mpm) or desc(bug) 1.812438 1.677608 1.613941 date(2015) or branch(default) 0.968276 0.896032 0.869017