view comparison.txt @ 2320:dbdce3b99988

fix parsing of tags. make parse errors useful. add new tag tests.

old code read every head of .hgtags. delete and recreate of .hgtags gave
new head, but if error in deleted rev, .hgtags had error messages every
time it was parsed. this was very hard to fix, because deleted revs hard
to get back and update, needed merges too.

new code reads .hgtags on every head. advantage is if parse error
happens with new code, is possible to fix them by editing .hgtags on a
head and committing.

NOTE: new code uses binary search of manifest of each head to be fast,
but still much slower than old code. best thing would be to have delete
record stored in filelog so we never touch manifest. could find live
heads directly from filelog. this is more work than i want now.

new tests check for parse of tags on different heads, and inaccessible
heads created by delete and recreate of .hgtags.

                    Mercurial      git                     BK (*)
storage             revlog delta   compressed revisions    SCCS weave
storage naming      by filename    by revision hash        by filename
merge               file DAGs      changeset DAG           file DAGs?
consistency         SHA1           SHA1                    CRC
signable?           yes            yes                     no

retrieve file tip   O(1)           O(1)                    O(revs)
add rev             O(1)           O(1)                    O(revs)
find prev file rev  O(1)           O(changesets)           O(revs)
annotate file       O(revs)        O(changesets)           O(revs)
find file changeset O(1)           O(changesets)           ?

checkout            O(files)       O(files)                O(revs)?
commit              O(changes)     O(changes)              ?
                    6 patches/s    6 patches/s             slow
diff working dir    O(changes)     O(changes)              ?
                    < 1s           < 1s                    ?
tree diff revs      O(changes)     O(changes)              ?
                    < 1s           < 1s                    ?
hardlink clone      O(files)       O(revisions)            O(files)

find remote csets   O(log new)     rsync: O(revisions)     ?
                                   git-http: O(changesets)
pull remote csets   O(patch)       O(modified files)       O(patch)

repo growth         O(patch)       O(revisions)            O(patch)
 kernel history     300M           3.5G?                   250M?
lines of code       2500           6500 (+ cogito)         ??

* I've never used BK so this is just guesses