<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
shadow	B-Application
paging	I-Application
is	O
a	O
technique	O
for	O
providing	O
atomicity	B-General_Concept
and	O
durability	O
(	O
two	O
of	O
the	O
ACID	O
properties	O
)	O
in	O
database	B-Application
systems	I-Application
.	O
</s>
<s>
A	O
page	O
in	O
this	O
context	O
refers	O
to	O
a	O
unit	O
of	O
physical	O
storage	O
(	O
probably	O
on	O
a	O
hard	B-Device
disk	I-Device
)	O
,	O
typically	O
of	O
the	O
order	O
of	O
1	O
to	O
64	O
KiB	O
.	O
</s>
<s>
Shadow	B-Application
paging	I-Application
is	O
a	O
copy-on-write	B-Language
technique	O
for	O
avoiding	O
in-place	B-Algorithm
updates	O
of	O
pages	O
.	O
</s>
<s>
Because	O
the	O
page	O
is	O
"	O
activated	O
"	O
only	O
when	O
it	O
is	O
ready	O
,	O
it	O
is	O
atomic	B-General_Concept
.	O
</s>
<s>
If	O
the	O
referring	O
pages	O
must	O
also	O
be	O
updated	O
via	O
shadow	B-Application
paging	I-Application
,	O
this	O
procedure	O
may	O
recurse	O
many	O
times	O
,	O
becoming	O
quite	O
costly	O
.	O
</s>
<s>
One	O
solution	O
,	O
employed	O
by	O
the	O
Write	B-Application
Anywhere	I-Application
File	I-Application
Layout	I-Application
(	O
WAFL	O
)	O
file	O
system	O
is	O
to	O
be	O
lazy	O
about	O
making	O
pages	O
durable	O
(	O
i.e.	O
,	O
write-behind	O
caching	O
)	O
.	O
</s>
<s>
Write-ahead	B-Algorithm
logging	I-Algorithm
is	O
a	O
more	O
popular	O
solution	O
that	O
uses	O
in-place	B-Algorithm
updates	O
.	O
</s>
<s>
Shadow	B-Application
paging	I-Application
is	O
similar	O
to	O
the	O
old	O
master	O
–	O
new	O
master	O
batch	O
processing	O
technique	O
used	O
in	O
mainframe	O
database	B-Application
systems	I-Application
.	O
</s>
<s>
Shadow	B-Application
paging	I-Application
is	O
also	O
similar	O
to	O
purely	B-Application
functional	I-Application
data	I-Application
structures	I-Application
,	O
in	O
that	O
in-place	B-Algorithm
updates	O
are	O
avoided	O
.	O
</s>
