revlog: use existing file handle when reading during _addrevision
_addrevision() may need to read from revlogs as part of computing
deltas. Previously, we would flush existing file handles and open
a new, short-lived file handle to perform the reading.
If we have an existing file handle, it seems logical to reuse it
for reading instead of opening a new file handle. This patch
makes that the new behavior.
After this patch, revlog files are only reopened when adding
revisions if the revlog is switched from inline to non-inline.
On Linux when unbundling a bundle of the mozilla-central repo, this
patch has the following impact on system call counts:
Call Before After Delta
write 827,639 673,390 -154,249
open 700,103 684,089 -16,014
read 74,489 74,489 0
fstat 493,924 461,896 -32,028
close 249,131 233,117 -16,014
stat 242,001 242,001 0
lstat 18,676 18,676 0
lseek 20,268 20,268 0
ioctl 14,652 13,173 -1,479
TOTAL 3,180,758 2,930,679 -250,079
It's worth noting that many of the open() calls fail due to missing
files. That's why there are many more open() calls than close().
Despite the significant system call reduction, this change does not
seem to have a significant performance impact on Linux.
On Windows 10 (not a VM, on a SSD), this patch appears to reduce
unbundle time for mozilla-central from ~960s to ~920s. This isn't
as significant as I was hoping. But a decrease it is nonetheless.
Still, Windows unbundle performance is still >2x slower than Linux.
Despite the lack of significant gains, fewer system calls is fewer
system calls. If nothing else, this will narrow the focus of potential
areas to optimize in the future.
setup repo
$ hg init t
$ cd t
$ echo a > a
$ hg commit -Am'add a'
adding a
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
$ hg parents
changeset: 0:1f0dee641bb7
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add a
rollback to null revision
$ hg status
$ hg rollback
repository tip rolled back to revision -1 (undo commit)
working directory now based on revision -1
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
0 files, 0 changesets, 0 total revisions
$ hg parents
$ hg status
A a
Two changesets this time so we rollback to a real changeset
$ hg commit -m'add a again'
$ echo a >> a
$ hg commit -m'modify a'
Test issue 902 (current branch is preserved)
$ hg branch test
marked working directory as branch test
(branches are permanent and global, did you want a bookmark?)
$ hg rollback
repository tip rolled back to revision 0 (undo commit)
working directory now based on revision 0
$ hg branch
default
Test issue 1635 (commit message saved)
$ cat .hg/last-message.txt ; echo
modify a
Test rollback of hg before issue 902 was fixed
$ hg commit -m "test3"
$ hg branch test
marked working directory as branch test
(branches are permanent and global, did you want a bookmark?)
$ rm .hg/undo.branch
$ hg rollback
repository tip rolled back to revision 0 (undo commit)
named branch could not be reset: current branch is still 'test'
working directory now based on revision 0
$ hg branch
test
working dir unaffected by rollback: do not restore dirstate et. al.
$ hg log --template '{rev} {branch} {desc|firstline}\n'
0 default add a again
$ hg status
M a
$ hg bookmark foo
$ hg commit -m'modify a again'
$ echo b > b
$ hg bookmark bar -r default #making bar active, before the transaction
$ hg commit -Am'add b'
adding b
$ hg log --template '{rev} {branch} {desc|firstline}\n'
2 test add b
1 test modify a again
0 default add a again
$ hg update bar
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
(activating bookmark bar)
$ cat .hg/undo.branch ; echo
test
$ hg rollback -f
repository tip rolled back to revision 1 (undo commit)
$ hg id -n
0
$ hg branch
default
$ cat .hg/bookmarks.current ; echo
bar
$ hg bookmark --delete foo bar
rollback by pretxncommit saves commit message (issue1635)
$ echo a >> a
$ hg --config hooks.pretxncommit=false commit -m"precious commit message"
transaction abort!
rollback completed
abort: pretxncommit hook exited with status * (glob)
[255]
$ cat .hg/last-message.txt ; echo
precious commit message
same thing, but run $EDITOR
$ cat > editor.sh << '__EOF__'
> echo "another precious commit message" > "$1"
> __EOF__
$ HGEDITOR="\"sh\" \"`pwd`/editor.sh\"" hg --config hooks.pretxncommit=false commit 2>&1
transaction abort!
rollback completed
note: commit message saved in .hg/last-message.txt
abort: pretxncommit hook exited with status * (glob)
[255]
$ cat .hg/last-message.txt
another precious commit message
test rollback on served repository
#if serve
$ hg commit -m "precious commit message"
$ hg serve -p $HGPORT -d --pid-file=hg.pid -A access.log -E errors.log
$ cat hg.pid >> $DAEMON_PIDS
$ cd ..
$ hg clone http://localhost:$HGPORT u
requesting all changes
adding changesets
adding manifests
adding file changes
added 3 changesets with 2 changes to 1 files (+1 heads)
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd u
$ hg id default
068774709090
now rollback and observe that 'hg serve' reloads the repository and
presents the correct tip changeset:
$ hg -R ../t rollback
repository tip rolled back to revision 1 (undo commit)
working directory now based on revision 0
$ hg id default
791dd2169706
#endif
update to older changeset and then refuse rollback, because
that would lose data (issue2998)
$ cd ../t
$ hg -q update
$ rm `hg status -un`
$ template='{rev}:{node|short} [{branch}] {desc|firstline}\n'
$ echo 'valuable new file' > b
$ echo 'valuable modification' >> a
$ hg commit -A -m'a valuable change'
adding b
$ hg update 0
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg rollback
abort: rollback of last commit while not checked out may lose data
(use -f to force)
[255]
$ hg tip -q
2:4d9cd3795eea
$ hg rollback -f
repository tip rolled back to revision 1 (undo commit)
$ hg status
$ hg log --removed b # yep, it's gone
same again, but emulate an old client that doesn't write undo.desc
$ hg -q update
$ echo 'valuable modification redux' >> a
$ hg commit -m'a valuable change redux'
$ rm .hg/undo.desc
$ hg update 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg rollback
rolling back unknown transaction
$ cat a
a
corrupt journal test
$ echo "foo" > .hg/store/journal
$ hg recover
rolling back interrupted transaction
couldn't read journal entry 'foo\n'!
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 2 changesets, 2 total revisions