<s>
SDCH	B-Algorithm
(	O
Shared	B-Algorithm
Dictionary	I-Algorithm
Compression	I-Algorithm
for	I-Algorithm
HTTP	I-Algorithm
)	O
is	O
a	O
data	B-General_Concept
compression	I-General_Concept
algorithm	I-General_Concept
created	O
by	O
Google	B-Application
,	O
based	O
on	O
VCDIFF	B-Application
(	O
RFC	B-Application
3284	I-Application
)	O
.	O
</s>
<s>
SDCH	B-Algorithm
achieves	O
its	O
effectiveness	O
by	O
using	O
pre-negotiated	O
dictionaries	O
to	O
"	O
warm	O
up	O
"	O
its	O
internal	O
state	O
prior	O
to	O
encoding	O
or	O
decoding	O
.	O
</s>
<s>
It	O
was	O
supported	O
natively	O
in	O
Google	B-Application
Chrome	I-Application
,	O
Chromium	O
,	O
and	O
Android	O
,	O
as	O
well	O
as	O
on	O
Google	B-Application
websites	O
.	O
</s>
<s>
SDCH	B-Algorithm
compression	O
was	O
removed	O
from	O
Google	B-Application
Chrome	I-Application
,	O
and	O
other	O
Chromium	O
products	O
,	O
in	O
version	O
59	O
(	O
2017-06-05	O
)	O
.	O
</s>
<s>
Due	O
to	O
the	O
diffing	O
results	O
and	O
the	O
data	O
being	O
compressed	O
with	O
the	O
same	O
coding	O
,	O
SDCH	B-Algorithm
dictionaries	O
aged	O
relatively	O
quickly	O
and	O
compression	O
density	O
became	O
quickly	O
worse	O
than	O
with	O
the	O
usual	O
non-dictionary	O
compression	O
such	O
as	O
GZip	O
.	O
</s>
<s>
Modern	O
dictionary	O
coding	O
such	O
as	O
Shared	O
Brotli	B-Application
has	O
a	O
more	O
effective	O
solution	O
for	O
this	O
that	O
fixes	O
the	O
dictionary	O
aging	O
problem	O
.	O
</s>
