<s>
Mercurial	B-Protocol
is	O
a	O
distributed	B-Protocol
revision	I-Protocol
control	I-Protocol
tool	O
for	O
software	B-Application
developers	I-Application
.	O
</s>
<s>
It	O
is	O
supported	O
on	O
Microsoft	B-Application
Windows	I-Application
and	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
such	O
as	O
FreeBSD	B-Operating_System
,	O
macOS	B-Application
,	O
and	O
Linux	B-Operating_System
.	O
</s>
<s>
Mercurial	B-Protocol
's	O
major	O
design	O
goals	O
include	O
high	O
performance	O
and	O
scalability	O
,	O
decentralization	O
,	O
fully	O
distributed	O
collaborative	O
development	O
,	O
robust	O
handling	O
of	O
both	O
plain	O
text	O
and	O
binary	O
files	O
,	O
and	O
advanced	O
branching	O
and	O
merging	O
capabilities	O
,	O
while	O
remaining	O
conceptually	O
simple	O
.	O
</s>
<s>
Mercurial	B-Protocol
has	O
also	O
taken	O
steps	O
to	O
ease	O
the	O
transition	O
for	O
users	O
of	O
other	O
version	B-Architecture
control	I-Architecture
systems	I-Architecture
,	O
particularly	O
Subversion	B-Application
.	O
</s>
<s>
Mercurial	B-Protocol
is	O
primarily	O
a	O
command-line	B-Application
driven	O
program	O
,	O
but	O
graphical	B-Application
user	I-Application
interface	I-Application
extensions	O
are	O
available	O
,	O
e.g.	O
</s>
<s>
TortoiseHg	B-Protocol
,	O
and	O
several	O
IDEs	B-Application
offer	O
support	O
for	O
version	B-Architecture
control	I-Architecture
with	O
Mercurial	B-Protocol
.	O
</s>
<s>
All	O
of	O
Mercurial	B-Protocol
's	O
operations	O
are	O
invoked	O
as	O
arguments	O
to	O
its	O
driver	O
program	O
hg	B-Protocol
(	O
a	O
reference	O
to	O
Hg	B-Protocol
–	O
the	O
chemical	O
symbol	O
of	O
the	O
element	O
mercury	O
)	O
.	O
</s>
<s>
Olivia	O
Mackall	O
originated	O
Mercurial	B-Protocol
and	O
served	O
as	O
its	O
lead	O
developer	B-Application
until	O
late	O
2016	O
.	O
</s>
<s>
Mercurial	B-Protocol
is	O
released	O
as	O
free	B-Application
software	I-Application
under	O
the	O
GPL-2.0-or-later	B-License
license	O
.	O
</s>
<s>
It	O
is	O
mainly	O
implemented	O
using	O
the	O
Python	B-Language
programming	I-Language
language	I-Language
,	O
but	O
includes	O
a	O
binary	O
diff	B-Application
implementation	O
written	O
in	O
C	B-Language
.	O
</s>
<s>
Mackall	O
first	O
announced	O
Mercurial	B-Protocol
on	O
19	O
April	O
2005	O
.	O
</s>
<s>
The	O
impetus	O
for	O
this	O
was	O
the	O
announcement	O
earlier	O
that	O
month	O
by	O
Bitmover	B-Protocol
that	O
they	O
were	O
withdrawing	O
the	O
free	O
version	O
of	O
BitKeeper	B-Protocol
because	O
of	O
the	O
development	O
of	O
SourcePuller	B-Language
.	O
</s>
<s>
BitKeeper	B-Protocol
had	O
been	O
used	O
for	O
the	O
version	B-Architecture
control	I-Architecture
requirements	O
of	O
the	O
Linux	B-Application
kernel	I-Application
project	O
.	O
</s>
<s>
Mackall	O
decided	O
to	O
write	O
a	O
distributed	B-Protocol
version	I-Protocol
control	I-Protocol
system	I-Protocol
as	O
a	O
replacement	O
for	O
use	O
with	O
the	O
Linux	B-Application
kernel	I-Application
.	O
</s>
<s>
This	O
project	O
started	O
a	O
few	O
days	O
after	O
the	O
now	O
well-known	O
Git	B-Application
project	O
was	O
initiated	O
by	O
Linus	O
Torvalds	O
with	O
similar	O
aims	O
.	O
</s>
<s>
The	O
Linux	B-Application
kernel	I-Application
project	O
decided	O
to	O
use	O
Git	B-Application
rather	O
than	O
Mercurial	B-Protocol
,	O
but	O
Mercurial	B-Protocol
is	O
now	O
used	O
by	O
many	O
other	O
projects	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
In	O
an	O
answer	O
on	O
the	O
Mercurial	B-Protocol
mailing	O
list	O
,	O
Olivia	O
Mackall	O
explained	O
how	O
the	O
name	O
"	O
Mercurial	B-Protocol
"	O
was	O
chosen	O
:	O
</s>
<s>
High-profile	O
projects	O
such	O
as	O
the	O
OpenJDK	B-Language
have	O
used	O
Mercurial	B-Protocol
in	O
the	O
past	O
,	O
though	O
the	O
OpenJDK	B-Language
no	O
longer	O
does	O
as	O
of	O
Java	O
16	O
.	O
</s>
<s>
Mercurial	B-Protocol
uses	O
SHA-1	B-Algorithm
hashes	I-Algorithm
to	O
identify	O
revisions	O
.	O
</s>
<s>
For	O
repository	O
access	O
via	O
a	O
network	O
,	O
Mercurial	B-Protocol
uses	O
an	O
HTTP-based	O
protocol	O
that	O
seeks	O
to	O
reduce	O
round-trip	O
requests	O
,	O
new	O
connections	O
,	O
and	O
data	O
transferred	O
.	O
</s>
<s>
Mercurial	B-Protocol
can	O
also	O
work	O
over	O
SSH	B-Protocol
where	O
the	O
protocol	O
is	O
very	O
similar	O
to	O
the	O
HTTP-based	O
protocol	O
.	O
</s>
<s>
Figure	O
1	O
shows	O
some	O
of	O
the	O
most	O
important	O
operations	O
in	O
Mercurial	B-Protocol
and	O
their	O
relations	O
to	O
Mercurial	B-Protocol
's	O
concepts	O
.	O
</s>
<s>
Although	O
Mercurial	B-Protocol
was	O
not	O
selected	O
to	O
manage	O
the	O
Linux	B-Application
kernel	I-Application
sources	O
,	O
it	O
has	O
been	O
adopted	O
by	O
several	O
organizations	O
,	O
including	O
Facebook	B-Application
,	O
the	O
W3C	O
,	O
and	O
Mozilla	B-Operating_System
.	O
</s>
<s>
Facebook	B-Application
is	O
using	O
the	O
Rust	B-Application
programming	I-Application
language	I-Application
to	O
write	O
Mononoke	O
,	O
a	O
Mercurial	B-Protocol
server	O
specifically	O
designed	O
to	O
support	O
large	O
multi-project	O
repositories	O
.	O
</s>
<s>
In	O
2013	O
,	O
Facebook	B-Application
adopted	O
Mercurial	B-Protocol
and	O
began	O
work	O
on	O
scaling	O
it	O
to	O
handle	O
their	O
large	O
,	O
unified	O
code	O
repository	O
.	O
</s>
<s>
Google	O
also	O
uses	O
Mercurial	B-Protocol
client	O
as	O
a	O
front-end	O
on	O
their	O
cloud-based	O
'	O
Piper	O
 '	O
monorepo	O
back-end	O
.	O
</s>
<s>
Bitbucket	B-Protocol
announced	O
that	O
its	O
web-based	O
version	B-Architecture
control	I-Architecture
services	O
would	O
end	O
support	O
for	O
Mercurial	B-Protocol
in	O
June	O
2020	O
(	O
then	O
extended	O
to	O
July	O
2020	O
)	O
,	O
explaining	O
that	O
"	O
less	O
than	O
1%	O
of	O
new	O
projects	O
use	O
it	O
,	O
and	O
developer	B-Application
surveys	O
indicated	O
that	O
90%	O
of	O
developers	B-Application
use	O
Git	B-Application
"	O
.	O
</s>
<s>
RhodeCode	B-Protocol
by	O
RhodeCode	B-Protocol
Inc	O
.	O
</s>
<s>
The	O
following	O
websites	O
provide	O
free	B-Application
source	I-Application
code	O
hosting	O
for	O
Mercurial	B-Protocol
repositories	O
:	O
</s>
<s>
Some	O
projects	O
using	O
the	O
Mercurial	B-Protocol
distributed	O
RCS	O
:	O
</s>
