<s>
Slony-I	B-Language
is	O
an	O
asynchronous	O
master-slave	B-Architecture
replication	I-Architecture
system	O
for	O
the	O
PostgreSQL	B-Application
DBMS	O
,	O
providing	O
support	O
for	O
cascading	O
and	O
failover	B-General_Concept
.	O
</s>
<s>
Asynchronous	O
means	O
that	O
when	O
a	O
database	B-General_Concept
transaction	I-General_Concept
has	O
been	O
committed	O
to	O
the	O
master	O
server	O
,	O
it	O
is	O
not	O
yet	O
guaranteed	O
to	O
be	O
available	O
in	O
slaves	O
.	O
</s>
<s>
Cascading	O
means	O
that	O
replicas	B-Architecture
can	O
be	O
created	O
(	O
and	O
updated	O
)	O
via	O
other	O
replicas	B-Architecture
,	O
i.e.	O
</s>
<s>
The	O
name	O
"	O
slony	B-Language
"	O
comes	O
from	O
the	O
Russian	O
word	O
"	O
слоны	O
"	O
which	O
means	O
"	O
elephants	O
"	O
.	O
</s>
<s>
This	O
is	O
a	O
reference	O
to	O
the	O
PostgreSQL	B-Application
elephant	O
logo	O
,	O
as	O
well	O
as	O
being	O
a	O
"	O
tip	O
of	O
the	O
hat	O
"	O
to	O
Vadim	O
Mikheev	O
,	O
who	O
came	O
up	O
with	O
some	O
of	O
the	O
core	O
ideas	O
Slony-I	B-Language
uses	O
to	O
work	O
.	O
</s>
<s>
Unlike	O
many	O
other	O
replication	B-Architecture
solutions	O
for	O
PostgreSQL	B-Application
,	O
Slony-I	B-Language
is	O
not	O
tied	O
to	O
any	O
particular	O
version	O
of	O
the	O
database	O
,	O
which	O
makes	O
it	O
possible	O
to	O
upgrade	O
a	O
database	O
cluster	O
one	O
node	O
at	O
a	O
time	O
,	O
without	O
material	O
downtime	O
.	O
</s>
