wireproto: add request IDs to frames
One of my primary goals with the new wire protocol is to make
operations faster and enable both client and server-side
operations to scale to multiple CPU cores.
One of the ways we make server interactions faster is by reducing
the number of round trips to that server.
With the existing wire protocol, the "batch" command facilitates
executing multiple commands from a single request payload. The way
it works is the requests for multiple commands are serialized. The
server executes those commands sequentially then serializes all
their results. As an optimization for reducing round trips, this
is very effective. The technical implementation, however, is pretty
bad and suffers from a number of deficiencies. For example, it
creates a new place where authorization to run a command must be
checked. (The lack of this checking in older Mercurial releases
was CVE-2018-1000132.)
The principles behind the "batch" command are sound. However, the
execution is not. Therefore, I want to ditch "batch" in the
new wire protocol and have protocol level support for issuing
multiple requests in a single round trip.
This commit introduces support in the frame-based wire protocol to
facilitate this. We do this by adding a "request ID" to each frame.
If a server sees frames associated with different "request IDs," it
handles them as separate requests. All of this happening possibly
as part of the same message from client to server (the same request
body in the case of HTTP).
We /could/ model the exchange the way pipelined HTTP requests do,
where the server processes requests in order they are issued and
received. But this artifically constrains scalability. A better
model is to allow multi-requests to be executed concurrently and
for responses to be sent and handled concurrently. So the
specification explicitly allows this. There is some work to be done
around specifying dependencies between multi-requests. We take
the easy road for now and punt on this problem, declaring that
if order is important, clients must not issue the request until
responses to dependent requests have been received.
This commit focuses on the boilerplate of implementing the request
ID. The server reactor still can't manage multiple, in-flight
request IDs. This will be addressed in a subsequent commit.
Because the wire semantics have changed, we bump the version of the
media type.
Differential Revision: https://phab.mercurial-scm.org/D2869
#require cvs112
This feature requires use of builtin cvsps!
$ echo "[extensions]" >> $HGRCPATH
$ echo "convert = " >> $HGRCPATH
create cvs repository with one project
$ mkdir cvsrepo
$ cd cvsrepo
$ CVSROOT=`pwd`
$ export CVSROOT
$ CVS_OPTIONS=-f
$ export CVS_OPTIONS
$ cd ..
$ rmdir cvsrepo
$ cvscall()
> {
> cvs -f "$@"
> }
output of 'cvs ci' varies unpredictably, so just discard it
$ cvsci()
> {
> sleep 1
> cvs -f ci "$@" >/dev/null
> }
$ cvscall -d "$CVSROOT" init
$ mkdir cvsrepo/proj
$ cvscall -q co proj
create file1 on the trunk
$ cd proj
$ touch file1
$ cvscall -Q add file1
$ cvsci -m"add file1 on trunk" file1
create two branches
$ cvscall -q tag -b v1_0
T file1
$ cvscall -q tag -b v1_1
T file1
create file2 on branch v1_0
$ cvscall -Q up -rv1_0
$ touch file2
$ cvscall -Q add file2
$ cvsci -m"add file2" file2
create file3, file4 on branch v1_1
$ cvscall -Q up -rv1_1
$ touch file3
$ touch file4
$ cvscall -Q add file3 file4
$ cvsci -m"add file3, file4 on branch v1_1" file3 file4
merge file2 from v1_0 to v1_1
$ cvscall -Q up -jv1_0
$ cvsci -m"MERGE from v1_0: add file2"
cvs commit: Examining .
Step things up a notch: now we make the history really hairy, with
changes bouncing back and forth between trunk and v1_2 and merges
going both ways. (I.e., try to model the real world.)
create branch v1_2
$ cvscall -Q up -A
$ cvscall -q tag -b v1_2
T file1
create file5 on branch v1_2
$ cvscall -Q up -rv1_2
$ touch file5
$ cvs -Q add file5
$ cvsci -m"add file5 on v1_2"
cvs commit: Examining .
create file6 on trunk post-v1_2
$ cvscall -Q up -A
$ touch file6
$ cvscall -Q add file6
$ cvsci -m"add file6 on trunk post-v1_2"
cvs commit: Examining .
merge file5 from v1_2 to trunk
$ cvscall -Q up -A
$ cvscall -Q up -jv1_2 file5
$ cvsci -m"MERGE from v1_2: add file5"
cvs commit: Examining .
merge file6 from trunk to v1_2
$ cvscall -Q up -rv1_2
$ cvscall up -jHEAD file6
U file6
$ cvsci -m"MERGE from HEAD: add file6"
cvs commit: Examining .
cvs rlog output
$ cvscall -q rlog proj | egrep '^(RCS file|revision)'
RCS file: $TESTTMP/cvsrepo/proj/file1,v
revision 1.1
RCS file: $TESTTMP/cvsrepo/proj/Attic/file2,v
revision 1.1
revision 1.1.4.2
revision 1.1.4.1
revision 1.1.2.1
RCS file: $TESTTMP/cvsrepo/proj/Attic/file3,v
revision 1.1
revision 1.1.2.1
RCS file: $TESTTMP/cvsrepo/proj/Attic/file4,v
revision 1.1
revision 1.1.2.1
RCS file: $TESTTMP/cvsrepo/proj/file5,v
revision 1.2
revision 1.1
revision 1.1.2.1
RCS file: $TESTTMP/cvsrepo/proj/file6,v
revision 1.1
revision 1.1.2.2
revision 1.1.2.1
convert to hg (#1)
$ cd ..
$ hg convert --datesort proj proj.hg
initializing destination proj.hg repository
connecting to $TESTTMP/cvsrepo
scanning source...
collecting CVS rlog
15 log entries
creating changesets
9 changeset entries
sorting...
converting...
8 add file1 on trunk
7 add file2
6 MERGE from v1_0: add file2
5 file file3 was initially added on branch v1_1.
4 add file3, file4 on branch v1_1
3 add file5 on v1_2
2 add file6 on trunk post-v1_2
1 MERGE from HEAD: add file6
0 MERGE from v1_2: add file5
hg log -G output (#1)
$ hg -R proj.hg log -G --template "{rev} {desc}\n"
o 8 MERGE from v1_2: add file5
|
| o 7 MERGE from HEAD: add file6
| |
o | 6 add file6 on trunk post-v1_2
| |
| o 5 add file5 on v1_2
| |
| | o 4 add file3, file4 on branch v1_1
| | |
o | | 3 file file3 was initially added on branch v1_1.
|/ /
| o 2 MERGE from v1_0: add file2
|/
| o 1 add file2
|/
o 0 add file1 on trunk
convert to hg (#2: with merge detection)
$ hg convert \
> --config convert.cvsps.mergefrom='"^MERGE from (\S+):"' \
> --datesort \
> proj proj.hg2
initializing destination proj.hg2 repository
connecting to $TESTTMP/cvsrepo
scanning source...
collecting CVS rlog
15 log entries
creating changesets
9 changeset entries
sorting...
converting...
8 add file1 on trunk
7 add file2
6 MERGE from v1_0: add file2
5 file file3 was initially added on branch v1_1.
4 add file3, file4 on branch v1_1
3 add file5 on v1_2
2 add file6 on trunk post-v1_2
1 MERGE from HEAD: add file6
0 MERGE from v1_2: add file5
hg log -G output (#2)
$ hg -R proj.hg2 log -G --template "{rev} {desc}\n"
o 8 MERGE from v1_2: add file5
|
| o 7 MERGE from HEAD: add file6
| |
o | 6 add file6 on trunk post-v1_2
| |
| o 5 add file5 on v1_2
| |
| | o 4 add file3, file4 on branch v1_1
| | |
o | | 3 file file3 was initially added on branch v1_1.
|/ /
| o 2 MERGE from v1_0: add file2
|/
| o 1 add file2
|/
o 0 add file1 on trunk