changegroup: compute seen files as changesets are added (
issue4750)
Before this patch, addchangegroup() would walk the changelog and compute
the set of seen files between applying changesets and applying
manifests. When cloning large repositories such as mozilla-central,
this consumed a non-trivial amount of time. On my MBP, this walk takes
~10s. On a dainty EC2 instance, this was measured to take ~125s! On the
latter machine, this delay was enough for the Mercurial server to
disconnect the client, thinking it had timed out, thus causing a clone
to abort.
This patch enables the changelog to compute the set of changed files as
new revisions are added. By doing so, we:
* avoid a potentially heavy computation between changelog and manifest
processing by spreading the computation across all changelog additions
* avoid extra reads from the changelog by operating on the data as it is
added
The downside of this is that the add revision callback does result in
extra I/O. Before, we would perform a flush (and subsequent read to
construct the full revision) when new delta chains were created. For
changelogs, this is typically every 2-4 revisions. Using the callback
guarantees there will be a flush after every added revision *and* an
open + read of the changelog to obtain the full revision in order to
read the added files. So, this increases the frequency of these
operations by the average chain length. In the future, the revlog
should be smart enough to know how to read revisions that haven't been
flushed yet, thus eliminating this extra I/O.
On my MBP, the total CPU times for an `hg unbundle` with a local
mozilla-central gzip bundle containing 251,934 changesets and 211,065
files did not have a statistically significant change with this patch,
holding steady around 360s. So, the increased revlog flushing did not
have an effect.
With this patch, there is no longer a visible pause between applying
changeset and manifest data. Before, it sure felt like Mercurial was
lethargic making this transition. Now, the transition is nearly
instantaneous, giving the impression that Mercurial is faster. Of course,
eliminating this pause means that the potential for network disconnect due
to channel inactivity during the changelog walk is eliminated as well.
And that is the impetus behind this change.
$ echo "[extensions]" >> $HGRCPATH
$ echo "rebase=" >> $HGRCPATH
initialize repository
$ hg init
$ echo 'a' > a
$ hg ci -A -m "0"
adding a
$ echo 'b' > b
$ hg ci -A -m "1"
adding b
$ hg up 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo 'c' > c
$ hg ci -A -m "2"
adding c
created new head
$ echo 'd' > d
$ hg ci -A -m "3"
adding d
$ hg bookmark -r 1 one
$ hg bookmark -r 3 two
$ hg up -q two
bookmark list
$ hg bookmark
one 1:925d80f479bb
* two 3:2ae46b1d99a7
rebase
$ hg rebase -s two -d one
rebasing 3:2ae46b1d99a7 "3" (tip two)
saved backup bundle to $TESTTMP/.hg/strip-backup/2ae46b1d99a7-e6b057bc-backup.hg (glob)
$ hg log
changeset: 3:42e5ed2cdcf4
bookmark: two
tag: tip
parent: 1:925d80f479bb
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 3
changeset: 2:db815d6d32e6
parent: 0:f7b1eb17ad24
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 2
changeset: 1:925d80f479bb
bookmark: one
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 1
changeset: 0:f7b1eb17ad24
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 0
aborted rebase should restore active bookmark.
$ hg up 1
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
(leaving bookmark two)
$ echo 'e' > d
$ hg ci -A -m "4"
adding d
created new head
$ hg bookmark three
$ hg rebase -s three -d two
rebasing 4:dd7c838e8362 "4" (tip three)
merging d
warning: conflicts during merge.
merging d incomplete! (edit conflicts, then use 'hg resolve --mark')
unresolved conflicts (see hg resolve, then hg rebase --continue)
[1]
$ hg rebase --abort
rebase aborted
$ hg bookmark
one 1:925d80f479bb
* three 4:dd7c838e8362
two 3:42e5ed2cdcf4
after aborted rebase, restoring a bookmark that has been removed should not fail
$ hg rebase -s three -d two
rebasing 4:dd7c838e8362 "4" (tip three)
merging d
warning: conflicts during merge.
merging d incomplete! (edit conflicts, then use 'hg resolve --mark')
unresolved conflicts (see hg resolve, then hg rebase --continue)
[1]
$ hg bookmark -d three
$ hg rebase --abort
rebase aborted
$ hg bookmark
one 1:925d80f479bb
two 3:42e5ed2cdcf4