tests/test-debugbundle.t
author Durham Goode <durham@fb.com>
Sun, 30 Aug 2015 13:58:11 -0700
changeset 26117 4dc5b51f38fe
parent 23748 4ab66de46a96
child 26864 fb1217cea400
permissions -rw-r--r--
revlog: change generaldelta delta parent heuristic The old generaldelta heuristic was "if p1 (or p2) was closer than the last full text, use it, otherwise use prev". This was problematic when a repo contained multiple branches that were very different. If commits to branch A were pushed, and the last full text was branch B, it would generate a fulltext. Then if branch B was pushed, it would generate another fulltext. The problem is that the last fulltext (and delta'ing against `prev` in general) has no correlation with the contents of the incoming revision, and therefore will always have degenerate cases. According to the blame, that algorithm was chosen to minimize the chain length. Since there is already code that protects against that (the delta-vs-fulltext code), and since it has been improved since the original generaldelta algorithm went in (2011), I believe the chain length criteria will still be preserved. The new algorithm always diffs against p1 (or p2 if it's closer), unless the resulting delta will fail the delta-vs-fulltext check, in which case we delta against prev. Some before and after stats on manifest.d size. internal large repo old heuristic - 2.0 GB new heuristic - 1.2 GB mozilla-central old heuristic - 242 MB new heuristic - 261 MB The regression in mozilla central is due to the new heuristic choosing p2r as the delta when it's closer to the tip. Switching the algorithm to always prefer p1r brings the size back down (242 MB). This is result of the way in which mozilla does merges and pushes, and the result could easily swing the other direction in other repos (depending on if they merge X into Y or Y into X), but will never be as degenerate as before. I future patch will address the regression by introducing an optional, even more aggressive delta heuristic which will knock the mozilla manifest size down dramatically.


Create a test repository:

  $ hg init repo
  $ cd repo
  $ touch a ; hg add a ; hg ci -ma
  $ touch b ; hg add b ; hg ci -mb
  $ touch c ; hg add c ; hg ci -mc
  $ hg bundle --base 0 --rev tip bundle.hg -v
  2 changesets found
  uncompressed size of bundle content:
       332 (changelog)
       282 (manifests)
       105  b
       105  c

Terse output:

  $ hg debugbundle bundle.hg
  0e067c57feba1a5694ca4844f05588bb1bf82342
  991a3460af53952d10ec8a295d3d2cc2e5fa9690

Verbose output:

  $ hg debugbundle --all bundle.hg
  format: id, p1, p2, cset, delta base, len(delta)
  
  changelog
  0e067c57feba1a5694ca4844f05588bb1bf82342 3903775176ed42b1458a6281db4a0ccf4d9f287a 0000000000000000000000000000000000000000 0e067c57feba1a5694ca4844f05588bb1bf82342 3903775176ed42b1458a6281db4a0ccf4d9f287a 80
  991a3460af53952d10ec8a295d3d2cc2e5fa9690 0e067c57feba1a5694ca4844f05588bb1bf82342 0000000000000000000000000000000000000000 991a3460af53952d10ec8a295d3d2cc2e5fa9690 0e067c57feba1a5694ca4844f05588bb1bf82342 80
  
  manifest
  686dbf0aeca417636fa26a9121c681eabbb15a20 8515d4bfda768e04af4c13a69a72e28c7effbea7 0000000000000000000000000000000000000000 0e067c57feba1a5694ca4844f05588bb1bf82342 8515d4bfda768e04af4c13a69a72e28c7effbea7 55
  ae25a31b30b3490a981e7b96a3238cc69583fda1 686dbf0aeca417636fa26a9121c681eabbb15a20 0000000000000000000000000000000000000000 991a3460af53952d10ec8a295d3d2cc2e5fa9690 686dbf0aeca417636fa26a9121c681eabbb15a20 55
  
  b
  b80de5d138758541c5f05265ad144ab9fa86d1db 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 0e067c57feba1a5694ca4844f05588bb1bf82342 0000000000000000000000000000000000000000 12
  
  c
  b80de5d138758541c5f05265ad144ab9fa86d1db 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 991a3460af53952d10ec8a295d3d2cc2e5fa9690 0000000000000000000000000000000000000000 12

  $ cd ..