lfs: fix the stall and corruption issue when concurrently uploading blobs
We've avoided the issue up to this point by gating worker usage with an
experimental config. See 10e62d5efa73, and the thread linked there for some of
the initial diagnosis, but essentially some data was being read from the blob
before an error occurred and `keepalive` retried, but didn't rewind the file
pointer. So the leading data was lost from the blob on the server, and the
connection stalled, trying to send more data than available.
In trying to recreate this, I was unable to do so uploading from Windows to
CentOS 7. But it reproduced every time going from CentOS 7 to another CentOS 7
over https.
I found recent fixes in the FaceBook repo to address this[1][2]. The commit
message for the first is:
The KeepAlive HTTP implementation is bugged in it's retry logic, it supports
reading from a file pointer, but doesn't support rewinding of the seek cursor
when it performs a retry. So it can happen that an upload fails for whatever
reason and will then 'hang' on the retry event.
The sequence of events that get triggered are:
- Upload file A, goes OK. Keep-Alive caches connection.
- Upload file B, fails due to (for example) failing Keep-Alive, but LFS file
pointer has been consumed for the upload and fd has been closed.
- Retry for file B starts, sets the Content-Length properly to the expected
file size, but since file pointer has been consumed no data will be uploaded,
causing the server to wait for the uploaded data until either client or
server reaches a timeout, making it seem as our mercurial process hangs.
This is just a stop-gap measure to prevent this behavior from blocking Mercurial
(LFS has retry logic). A proper solutions need to be build on top of this
stop-gap measure: for upload from file pointers, we should support fseek() on
the interface. Since we expect to consume the whole file always anyways, this
should be safe. This way we can seek back to the beginning on a retry.
I ported those two patches, and it works. But I see that `url._sendfile()` does
a rewind on `httpsendfile` objects[3], so maybe it's better to keep this all in
one place and avoid a second seek. We may still want the first FaceBook patch
as extra protection for this problem in general. The other two uses of
`httpsendfile` are in the wire protocol to upload bundles, and to upload
largefiles. Neither of these appear to use a worker, and I'm not sure why
workers seem to trigger this, or if this could have happened without a worker.
Since `httpsendfile` already has a `close()` method, that is dropped. That
class also explicitly says there's no `__len__` attribute, so that is removed
too. The override for `read()` is necessary to avoid the progressbar usage per
file.
[1] https://github.com/facebookexperimental/eden/commit/c350d6536d90c044c837abdd3675185644481469
[2] https://github.com/facebookexperimental/eden/commit/77f0d3fd0415e81b63e317e457af9c55c46103ee
[3] https://www.mercurial-scm.org/repo/hg/file/5.2.2/mercurial/url.py#l176
Differential Revision: https://phab.mercurial-scm.org/D7962
Create configuration
$ echo "[ui]" >> $HGRCPATH
$ echo "interactive=true" >> $HGRCPATH
help qrefresh (no record)
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg help qrefresh
hg qrefresh [-I] [-X] [-e] [-m TEXT] [-l FILE] [-s] [FILE]...
update the current patch
If any file patterns are provided, the refreshed patch will contain only
the modifications that match those patterns; the remaining modifications
will remain in the working directory.
If -s/--short is specified, files currently included in the patch will be
refreshed just like matched files and remain in the patch.
If -e/--edit is specified, Mercurial will start your configured editor for
you to enter a message. In case qrefresh fails, you will find a backup of
your message in ".hg/last-message.txt".
hg add/remove/copy/rename work as usual, though you might want to use git-
style patches (-g/--git or [diff] git=1) to track copies and renames. See
the diffs help topic for more information on the git diff format.
Returns 0 on success.
options ([+] can be repeated):
-e --edit invoke editor on commit messages
-g --git use git extended diff format
-s --short refresh only files already in the patch and
specified files
-U --currentuser add/update author field in patch with current user
-u --user USER add/update author field in patch with given user
-D --currentdate add/update date field in patch with current date
-d --date DATE add/update date field in patch with given date
-I --include PATTERN [+] include names matching the given patterns
-X --exclude PATTERN [+] exclude names matching the given patterns
-m --message TEXT use text as commit message
-l --logfile FILE read commit message from file
(some details hidden, use --verbose to show complete help)
help qrefresh (record)
$ echo "record=" >> $HGRCPATH
$ hg help qrefresh
hg qrefresh [-I] [-X] [-e] [-m TEXT] [-l FILE] [-s] [FILE]...
update the current patch
If any file patterns are provided, the refreshed patch will contain only
the modifications that match those patterns; the remaining modifications
will remain in the working directory.
If -s/--short is specified, files currently included in the patch will be
refreshed just like matched files and remain in the patch.
If -e/--edit is specified, Mercurial will start your configured editor for
you to enter a message. In case qrefresh fails, you will find a backup of
your message in ".hg/last-message.txt".
hg add/remove/copy/rename work as usual, though you might want to use git-
style patches (-g/--git or [diff] git=1) to track copies and renames. See
the diffs help topic for more information on the git diff format.
Returns 0 on success.
options ([+] can be repeated):
-e --edit invoke editor on commit messages
-g --git use git extended diff format
-s --short refresh only files already in the patch and
specified files
-U --currentuser add/update author field in patch with current user
-u --user USER add/update author field in patch with given user
-D --currentdate add/update date field in patch with current date
-d --date DATE add/update date field in patch with given date
-I --include PATTERN [+] include names matching the given patterns
-X --exclude PATTERN [+] exclude names matching the given patterns
-m --message TEXT use text as commit message
-l --logfile FILE read commit message from file
-i --interactive interactively select changes to refresh
(some details hidden, use --verbose to show complete help)
$ hg init a
$ cd a
Base commit
$ cat > 1.txt <<EOF
> 1
> 2
> 3
> 4
> 5
> EOF
$ cat > 2.txt <<EOF
> a
> b
> c
> d
> e
> f
> EOF
$ mkdir dir
$ cat > dir/a.txt <<EOF
> hello world
>
> someone
> up
> there
> loves
> me
> EOF
$ hg add 1.txt 2.txt dir/a.txt
$ hg commit -m aaa
$ hg qrecord --config ui.interactive=false patch
abort: running non-interactively, use qnew instead
[255]
$ hg qnew -i --config ui.interactive=false patch
abort: running non-interactively
[255]
$ hg qnew -d '0 0' patch
Changing files
$ sed -e 's/2/2 2/;s/4/4 4/' 1.txt > 1.txt.new
$ sed -e 's/b/b b/' 2.txt > 2.txt.new
$ sed -e 's/hello world/hello world!/' dir/a.txt > dir/a.txt.new
$ mv -f 1.txt.new 1.txt
$ mv -f 2.txt.new 2.txt
$ mv -f dir/a.txt.new dir/a.txt
Whole diff
$ hg diff --nodates
diff -r ed27675cb5df 1.txt
--- a/1.txt
+++ b/1.txt
@@ -1,5 +1,5 @@
1
-2
+2 2
3
-4
+4 4
5
diff -r ed27675cb5df 2.txt
--- a/2.txt
+++ b/2.txt
@@ -1,5 +1,5 @@
a
-b
+b b
c
d
e
diff -r ed27675cb5df dir/a.txt
--- a/dir/a.txt
+++ b/dir/a.txt
@@ -1,4 +1,4 @@
-hello world
+hello world!
someone
up
partial qrefresh
$ hg qrefresh -i --config ui.interactive=false
abort: running non-interactively
[255]
$ hg qrefresh -i -d '0 0' <<EOF
> y
> y
> n
> y
> y
> n
> EOF
diff --git a/1.txt b/1.txt
2 hunks, 2 lines changed
examine changes to '1.txt'?
(enter ? for help) [Ynesfdaq?] y
@@ -1,3 +1,3 @@
1
-2
+2 2
3
record change 1/4 to '1.txt'?
(enter ? for help) [Ynesfdaq?] y
@@ -3,3 +3,3 @@
3
-4
+4 4
5
record change 2/4 to '1.txt'?
(enter ? for help) [Ynesfdaq?] n
diff --git a/2.txt b/2.txt
1 hunks, 1 lines changed
examine changes to '2.txt'?
(enter ? for help) [Ynesfdaq?] y
@@ -1,5 +1,5 @@
a
-b
+b b
c
d
e
record change 3/4 to '2.txt'?
(enter ? for help) [Ynesfdaq?] y
diff --git a/dir/a.txt b/dir/a.txt
1 hunks, 1 lines changed
examine changes to 'dir/a.txt'?
(enter ? for help) [Ynesfdaq?] n
After partial qrefresh 'tip'
$ hg tip -p
changeset: 1:0738af1a8211
tag: patch
tag: qbase
tag: qtip
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: [mq]: patch
diff -r 1fd39ab63a33 -r 0738af1a8211 1.txt
--- a/1.txt Thu Jan 01 00:00:00 1970 +0000
+++ b/1.txt Thu Jan 01 00:00:00 1970 +0000
@@ -1,5 +1,5 @@
1
-2
+2 2
3
4
5
diff -r 1fd39ab63a33 -r 0738af1a8211 2.txt
--- a/2.txt Thu Jan 01 00:00:00 1970 +0000
+++ b/2.txt Thu Jan 01 00:00:00 1970 +0000
@@ -1,5 +1,5 @@
a
-b
+b b
c
d
e
After partial qrefresh 'diff'
$ hg diff --nodates
diff -r 0738af1a8211 1.txt
--- a/1.txt
+++ b/1.txt
@@ -1,5 +1,5 @@
1
2 2
3
-4
+4 4
5
diff -r 0738af1a8211 dir/a.txt
--- a/dir/a.txt
+++ b/dir/a.txt
@@ -1,4 +1,4 @@
-hello world
+hello world!
someone
up
qrefresh interactively everything else
$ hg qrefresh -i -d '0 0' <<EOF
> y
> y
> y
> y
> EOF
diff --git a/1.txt b/1.txt
1 hunks, 1 lines changed
examine changes to '1.txt'?
(enter ? for help) [Ynesfdaq?] y
@@ -1,5 +1,5 @@
1
2 2
3
-4
+4 4
5
record change 1/2 to '1.txt'?
(enter ? for help) [Ynesfdaq?] y
diff --git a/dir/a.txt b/dir/a.txt
1 hunks, 1 lines changed
examine changes to 'dir/a.txt'?
(enter ? for help) [Ynesfdaq?] y
@@ -1,4 +1,4 @@
-hello world
+hello world!
someone
up
record change 2/2 to 'dir/a.txt'?
(enter ? for help) [Ynesfdaq?] y
After final qrefresh 'tip'
$ hg tip -p
changeset: 1:2c3f66afeed9
tag: patch
tag: qbase
tag: qtip
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: [mq]: patch
diff -r 1fd39ab63a33 -r 2c3f66afeed9 1.txt
--- a/1.txt Thu Jan 01 00:00:00 1970 +0000
+++ b/1.txt Thu Jan 01 00:00:00 1970 +0000
@@ -1,5 +1,5 @@
1
-2
+2 2
3
-4
+4 4
5
diff -r 1fd39ab63a33 -r 2c3f66afeed9 2.txt
--- a/2.txt Thu Jan 01 00:00:00 1970 +0000
+++ b/2.txt Thu Jan 01 00:00:00 1970 +0000
@@ -1,5 +1,5 @@
a
-b
+b b
c
d
e
diff -r 1fd39ab63a33 -r 2c3f66afeed9 dir/a.txt
--- a/dir/a.txt Thu Jan 01 00:00:00 1970 +0000
+++ b/dir/a.txt Thu Jan 01 00:00:00 1970 +0000
@@ -1,4 +1,4 @@
-hello world
+hello world!
someone
up
After qrefresh 'diff'
$ hg diff --nodates
$ cd ..