largefiles: optimize update speed by only updating changed largefiles
Historically, during 'hg update', every largefile in the working copy was
hashed (which is a very expensive operation on big files) and any
largefiles that did not have a hash that matched their standin were
updated.
This patch optimizes 'hg update' by keeping track of what standins have
changed between the old and new revisions, and only updating the largefiles
that have changed. This saves a lot of time by avoiding the unecessary
calculation of a list of sha1 hashes for big files.
With this patch, the time 'hg update' takes to complete is a function of
how many largefiles need to be updated and what their size is.
Performance tests on a repository with about 80 largefiles ranging from
a few MB to about 97 MB are shown below. The tests show how long it takes
to run 'hg update' with no changes actually being updated.
Mercurial 2.1 release:
$ time hg update
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
getting changed largefiles
0 largefiles updated, 0 removed
real 0m10.045s
user 0m9.367s
sys 0m0.674s
With this patch:
$ time hg update
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
real 0m0.965s
user 0m0.845s
sys 0m0.115s
The same repsoitory, without the largefiles extension enabled:
$ time hg update
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
real 0m0.799s
user 0m0.684s
sys 0m0.111s
So before the patch, 'hg update' with no changes was approximately 9.25s
slower with largefiles enabled. With this patch, it is approximately 0.165s
slower.
$ hg init
$ echo a > a
$ hg add a
$ hg commit -m "1"
$ hg status
$ hg copy a b
$ hg --config ui.portablefilenames=abort copy a con.xml
abort: filename contains 'con', which is reserved on Windows: 'con.xml'
[255]
$ hg status
A b
$ hg sum
parent: 0:c19d34741b0a tip
1
branch: default
commit: 1 copied
update: (current)
$ hg --debug commit -m "2"
b
b: copy a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3
committed changeset 1:93580a2c28a50a56f63526fb305067e6fbf739c4
we should see two history entries
$ hg history -v
changeset: 1:93580a2c28a5
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
files: b
description:
2
changeset: 0:c19d34741b0a
user: test
date: Thu Jan 01 00:00:00 1970 +0000
files: a
description:
1
we should see one log entry for a
$ hg log a
changeset: 0:c19d34741b0a
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 1
this should show a revision linked to changeset 0
$ hg debugindex a
rev offset length base linkrev nodeid p1 p2
0 0 3 0 0 b789fdd96dc2 000000000000 000000000000
we should see one log entry for b
$ hg log b
changeset: 1:93580a2c28a5
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 2
this should show a revision linked to changeset 1
$ hg debugindex b
rev offset length base linkrev nodeid p1 p2
0 0 65 0 1 37d9b5d994ea 000000000000 000000000000
this should show the rename information in the metadata
$ hg debugdata b 0 | head -3 | tail -2
copy: a
copyrev: b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3
$ $TESTDIR/md5sum.py .hg/store/data/b.i
4999f120a3b88713bbefddd195cf5133 .hg/store/data/b.i
$ hg cat b > bsum
$ $TESTDIR/md5sum.py bsum
60b725f10c9c85c70d97880dfe8191b3 bsum
$ hg cat a > asum
$ $TESTDIR/md5sum.py asum
60b725f10c9c85c70d97880dfe8191b3 asum
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
2 files, 2 changesets, 2 total revisions