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.
$ hg init test
$ cd test
$ echo 0 >> afile
$ hg add afile
$ hg commit -m "0.0"
$ echo 1 >> afile
$ hg commit -m "0.1"
$ echo 2 >> afile
$ hg commit -m "0.2"
$ echo 3 >> afile
$ hg commit -m "0.3"
$ hg update -C 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo 1 >> afile
$ hg commit -m "1.1"
created new head
$ echo 2 >> afile
$ hg commit -m "1.2"
$ echo a line > fred
$ echo 3 >> afile
$ hg add fred
$ hg commit -m "1.3"
$ hg mv afile adifferentfile
$ hg commit -m "1.3m"
$ hg update -C 3
1 files updated, 0 files merged, 2 files removed, 0 files unresolved
$ hg mv afile anotherfile
$ hg commit -m "0.3m"
$ hg debugindex -f 1 afile
rev flag offset length size ..... link p1 p2 nodeid (re)
0 0000 0 3 2 ..... 0 -1 -1 362fef284ce2 (re)
1 0000 3 5 4 ..... 1 0 -1 125144f7e028 (re)
2 0000 8 7 6 ..... 2 1 -1 4c982badb186 (re)
3 0000 15 9 8 ..... 3 2 -1 19b1fc555737 (re)
$ hg debugindex adifferentfile
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 75 ..... 7 2565f3199a74 000000000000 000000000000 (re)
$ hg debugindex anotherfile
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 75 ..... 8 2565f3199a74 000000000000 000000000000 (re)
$ hg debugindex fred
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 8 ..... 6 12ab3bcc5ea4 000000000000 000000000000 (re)
$ hg debugindex --manifest
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 48 ..... 0 43eadb1d2d06 000000000000 000000000000 (re)
1 48 48 ..... 1 8b89697eba2c 43eadb1d2d06 000000000000 (re)
2 96 48 ..... 2 626a32663c2f 8b89697eba2c 000000000000 (re)
3 144 48 ..... 3 f54c32f13478 626a32663c2f 000000000000 (re)
4 192 .. ..... 6 de68e904d169 626a32663c2f 000000000000 (re)
5 2.. 68 ..... 7 09bb521d218d de68e904d169 000000000000 (re)
6 3.. 54 ..... 8 1fde233dfb0f f54c32f13478 000000000000 (re)
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
4 files, 9 changesets, 7 total revisions
$ cd ..
$ for i in 0 1 2 3 4 5 6 7 8; do
> echo
> echo ---- hg clone -r "$i" test test-"$i"
> hg clone -r "$i" test test-"$i"
> cd test-"$i"
> hg verify
> cd ..
> done
---- hg clone -r 0 test test-0
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
---- hg clone -r 1 test test-1
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 1 files
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 2 changesets, 2 total revisions
---- hg clone -r 2 test test-2
adding changesets
adding manifests
adding file changes
added 3 changesets with 3 changes to 1 files
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 3 changesets, 3 total revisions
---- hg clone -r 3 test test-3
adding changesets
adding manifests
adding file changes
added 4 changesets with 4 changes to 1 files
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 4 changesets, 4 total revisions
---- hg clone -r 4 test test-4
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 1 files
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 2 changesets, 2 total revisions
---- hg clone -r 5 test test-5
adding changesets
adding manifests
adding file changes
added 3 changesets with 3 changes to 1 files
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 3 changesets, 3 total revisions
---- hg clone -r 6 test test-6
adding changesets
adding manifests
adding file changes
added 4 changesets with 5 changes to 2 files
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
2 files, 4 changesets, 5 total revisions
---- hg clone -r 7 test test-7
adding changesets
adding manifests
adding file changes
added 5 changesets with 6 changes to 3 files
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
3 files, 5 changesets, 6 total revisions
---- hg clone -r 8 test test-8
adding changesets
adding manifests
adding file changes
added 5 changesets with 5 changes to 2 files
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
2 files, 5 changesets, 5 total revisions
$ cd test-8
$ hg pull ../test-7
pulling from ../test-7
searching for changes
adding changesets
adding manifests
adding file changes
added 4 changesets with 2 changes to 3 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
4 files, 9 changesets, 7 total revisions
$ cd ..