<s>
Real-time	B-Application
database	I-Application
has	O
come	O
to	O
have	O
two	O
meanings	O
.	O
</s>
<s>
The	O
first	O
and	O
,	O
so	O
far	O
,	O
the	O
predominant	O
use	O
of	O
the	O
term	O
refers	O
to	O
a	O
database	B-Application
system	I-Application
which	O
uses	O
streaming	O
technologies	O
to	O
handle	O
workloads	O
whose	O
state	O
is	O
constantly	O
changing	O
.	O
</s>
<s>
This	O
differs	O
from	O
traditional	O
databases	B-Application
containing	O
persistent	B-Application
data	I-Application
,	O
mostly	O
unaffected	O
by	O
time	O
.	O
</s>
<s>
in	O
this	O
context	O
,	O
real-time	O
processing	O
means	O
that	O
a	O
transaction	B-General_Concept
is	O
processed	O
fast	O
enough	O
for	O
the	O
result	O
to	O
come	O
back	O
and	O
be	O
acted	O
on	O
right	O
away	O
.	O
</s>
<s>
Such	O
real-time	B-Application
databases	I-Application
are	O
useful	O
for	O
fraud	O
detection	O
,	O
recommendation	O
engines	O
,	O
audience	O
targeting	O
,	O
and	O
pricing	O
strategies	O
.	O
</s>
<s>
The	O
other	O
use	O
of	O
the	O
term	O
“	O
real-time	B-Application
database	I-Application
”	O
embodies	O
a	O
more	O
strict	O
definition	O
of	O
real-time	O
.	O
</s>
<s>
Hard	O
real-time	B-Application
database	I-Application
systems	O
enforce	O
temporal	O
validity	O
of	O
data	O
through	O
the	O
enforcement	O
of	O
database	B-General_Concept
transaction	I-General_Concept
deadlines	O
and	O
include	O
transaction	B-General_Concept
scheduling	O
policies	O
with	O
the	O
purpose	O
of	O
maximizing	O
the	O
ratio	O
of	O
successfully	O
committed	O
to	O
rolled-back	O
transactions	O
.	O
</s>
<s>
Unlike	O
other	O
database	B-Application
systems	I-Application
for	O
which	O
the	O
performance	O
metric	O
is	O
throughput	O
or	O
transactions-per-second	O
,	O
the	O
performance	O
metric	O
of	O
hard	O
real-time	B-Application
database	I-Application
systems	I-Application
is	O
the	O
ratio	O
of	O
committed-to-aborted	O
transactions	O
(	O
this	O
indicates	O
how	O
effective	O
the	O
transaction	B-General_Concept
scheduling	O
policy	O
is	O
)	O
and	O
meeting	O
the	O
deadline	O
100%	O
of	O
the	O
time	O
.	O
</s>
<s>
Hard	O
real-time	B-Application
databases	I-Application
,	O
through	O
enforcement	O
of	O
deadlines	O
,	O
do	O
not	O
allow	O
transactions	O
to	O
be	O
late	O
(	O
overrun	O
the	O
deadline	O
)	O
.	O
</s>
<s>
Real-time	B-Application
databases	I-Application
are	O
traditional	O
databases	B-Application
that	O
use	O
an	O
extension	O
to	O
give	O
the	O
additional	O
power	O
to	O
yield	O
reliable	O
responses	O
.	O
</s>
<s>
When	O
designing	O
a	O
real-time	B-Application
database	I-Application
system	O
,	O
one	O
should	O
consider	O
how	O
to	O
represent	O
valid	O
time	O
,	O
how	O
facts	O
are	O
associated	O
with	O
real-time	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Also	O
,	O
consider	O
how	O
to	O
represent	O
attribute	O
values	O
in	O
the	O
database	O
so	O
that	O
process	O
transactions	O
and	O
data	B-General_Concept
consistency	I-General_Concept
have	O
no	O
violations	O
.	O
</s>
<s>
For	O
example	O
,	O
an	O
air-traffic	B-Application
control	I-Application
system	O
constantly	O
monitors	O
hundreds	O
of	O
aircraft	O
and	O
makes	O
decisions	O
about	O
incoming	O
flight	O
paths	O
and	O
determines	O
the	O
order	O
in	O
which	O
aircraft	O
should	O
land	O
based	O
on	O
data	O
such	O
as	O
fuel	O
,	O
altitude	O
,	O
and	O
speed	O
.	O
</s>
<s>
Although	O
the	O
real-time	B-Application
database	I-Application
system	O
may	O
seem	O
like	O
a	O
simple	O
system	O
,	O
problems	O
arise	O
during	O
overload	O
when	O
two	O
or	O
more	O
database	B-General_Concept
transactions	I-General_Concept
require	O
access	O
to	O
the	O
same	O
portion	O
of	O
the	O
database	O
.	O
</s>
<s>
A	O
transaction	B-General_Concept
is	O
usually	O
the	O
result	O
of	O
an	O
execution	O
of	O
a	O
program	O
that	O
accesses	O
or	O
changes	O
the	O
contents	O
of	O
a	O
database	O
.	O
</s>
<s>
A	O
transaction	B-General_Concept
is	O
different	O
from	O
a	O
stream	O
because	O
a	O
stream	O
only	O
allows	O
read-only	O
operations	O
,	O
and	O
transactions	O
can	O
do	O
both	O
read	O
and	O
write	O
operations	O
.	O
</s>
<s>
A	O
database	O
must	O
let	O
only	O
one	O
transaction	B-General_Concept
operate	O
at	O
a	O
time	O
to	O
preserve	O
data	B-General_Concept
consistency	I-General_Concept
.	O
</s>
<s>
Real-time	B-Application
databases	I-Application
can	O
process	O
these	O
requests	O
utilizing	O
scheduling	O
algorithms	O
for	O
concurrency	B-Operating_System
control	I-Operating_System
,	O
prioritizing	O
both	O
students’	O
requests	O
in	O
some	O
way	O
.	O
</s>
<s>
In	O
real-time	B-Application
databases	I-Application
,	O
deadlines	O
are	O
formed	O
and	O
different	O
kinds	O
of	O
systems	O
respond	O
to	O
data	O
that	O
does	O
not	O
meet	O
its	O
deadline	O
in	O
different	O
ways	O
.	O
</s>
<s>
In	O
a	O
real-time	B-General_Concept
system	I-General_Concept
,	O
each	O
transaction	B-General_Concept
uses	O
a	O
timestamp	O
to	O
schedule	O
the	O
transactions	O
.	O
</s>
<s>
A	O
priority	O
mapper	O
unit	O
assigns	O
a	O
level	O
of	O
importance	O
to	O
each	O
transaction	B-General_Concept
upon	O
its	O
arrival	O
in	O
the	O
database	B-Application
system	I-Application
that	O
is	O
dependent	O
on	O
how	O
the	O
system	O
views	O
times	O
and	O
other	O
priorities	O
.	O
</s>
<s>
Earliest	O
DeadlinePT	O
=	O
DT	O
—	O
The	O
value	O
of	O
a	O
transaction	B-General_Concept
is	O
not	O
important	O
.	O
</s>
<s>
Relative	O
constraints	O
ensure	O
transactions	O
enter	O
into	O
the	O
system	O
at	O
the	O
same	O
time	O
as	O
the	O
rest	O
of	O
the	O
group	O
that	O
the	O
data	O
transaction	B-General_Concept
is	O
associated	O
with	O
.	O
</s>
<s>
An	O
additional	O
way	O
of	O
dealing	O
with	O
conflict	O
resolution	O
in	O
a	O
real-time	B-Application
database	I-Application
system	O
besides	O
deadlines	O
is	O
a	O
wait	O
policy	O
method	O
.	O
</s>
<s>
Deadlines	O
are	O
the	O
constraints	O
for	O
soon-to-be	O
replaced	O
data	O
accessed	O
by	O
the	O
transaction	B-General_Concept
.	O
</s>
<s>
Problems	O
arise	O
in	O
this	O
method	O
because	O
of	O
variations	O
caused	O
by	O
seek	O
time	O
variations	O
,	O
buffer	B-General_Concept
management	O
and	O
page	B-General_Concept
faults	I-General_Concept
.	O
</s>
<s>
It	O
builds	O
a	O
candidate	O
schedule	O
and	O
determines	O
if	O
a	O
transaction	B-General_Concept
would	O
miss	O
its	O
deadline	O
under	O
the	O
schedule	O
.	O
</s>
<s>
Should	O
a	O
transaction	B-General_Concept
miss	O
its	O
deadline	O
,	O
the	O
system	O
has	O
more	O
flexibility	O
and	O
the	O
transaction	B-General_Concept
may	O
increase	O
in	O
importance	O
.	O
</s>
<s>
Firm	O
deadline	O
Firm	O
deadlines	O
appear	O
to	O
be	O
similar	O
to	O
hard	O
deadlines	O
yet	O
they	O
differ	O
from	O
hard	O
deadlines	O
because	O
firm	O
deadlines	O
measure	O
how	O
important	O
it	O
is	O
to	O
complete	O
the	O
transaction	B-General_Concept
at	O
some	O
point	O
after	O
the	O
transaction	B-General_Concept
arrives	O
.	O
</s>
<s>
Sometimes	O
completing	O
a	O
transaction	B-General_Concept
after	O
its	O
deadline	O
has	O
expired	O
may	O
be	O
harmful	O
or	O
not	O
helpful	O
,	O
and	O
both	O
the	O
firm	O
and	O
hard	O
deadlines	O
consider	O
this	O
.	O
</s>
<s>
When	O
I	O
was	O
pre-selecting	O
classes	O
on	O
during	O
a	O
high	O
traffic	O
period	O
,	O
a	O
field	O
in	O
the	O
database	O
can	O
become	O
so	O
busy	O
with	O
registration	O
requests	O
that	O
it	O
was	O
unavailable	O
for	O
a	O
while	O
and	O
the	O
result	O
of	O
my	O
transaction	B-General_Concept
was	O
a	O
display	O
of	O
the	O
SQL	O
query	O
sent	O
and	O
a	O
message	O
that	O
said	O
that	O
the	O
data	O
is	O
currently	O
unavailable	O
.	O
</s>
<s>
With	O
large	O
real-time	B-Application
databases	I-Application
,	O
buffering	O
functions	O
can	O
help	O
improve	O
performance	O
tremendously	O
.	O
</s>
<s>
A	O
buffer	B-General_Concept
is	O
part	O
of	O
the	O
database	O
that	O
is	O
stored	O
in	O
main	O
memory	O
to	O
reduce	O
transaction	B-General_Concept
response	O
time	O
.	O
</s>
<s>
In	O
order	O
to	O
reduce	O
disk	O
input	O
and	O
output	O
transactions	O
,	O
a	O
certain	O
number	O
of	O
buffers	B-General_Concept
should	O
be	O
allocated	O
.	O
</s>
<s>
Sometimes	O
multiversions	O
are	O
stored	O
in	O
buffers	B-General_Concept
when	O
the	O
data	O
block	O
the	O
transaction	B-General_Concept
needs	O
is	O
currently	O
in	O
use	O
.	O
</s>
<s>
Different	O
strategies	O
allocate	O
buffers	B-General_Concept
and	O
must	O
balance	O
between	O
taking	O
an	O
excessive	O
amount	O
of	O
memory	O
and	O
having	O
everything	O
in	O
one	O
buffer	B-General_Concept
that	O
it	O
has	O
to	O
search	O
for	O
.	O
</s>
<s>
The	O
goal	O
is	O
to	O
eliminate	O
search	O
time	O
and	O
distribute	O
the	O
resources	O
between	O
buffer	B-General_Concept
frames	O
in	O
order	O
to	O
access	O
data	O
quickly	O
.	O
</s>
<s>
A	O
buffer	B-General_Concept
manager	O
is	O
capable	O
of	O
allocating	O
more	O
memory	O
,	O
if	O
necessary	O
,	O
to	O
improve	O
response	O
time	O
.	O
</s>
<s>
The	O
buffer	B-General_Concept
manager	O
can	O
even	O
determine	O
whether	O
a	O
transaction	B-General_Concept
that	O
it	O
has	O
should	O
advance	O
.	O
</s>
<s>
Buffering	O
can	O
improve	O
speed	O
in	O
real-time	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Traditional	O
databases	B-Application
are	O
persistent	O
but	O
are	O
incapable	O
of	O
dealing	O
with	O
dynamic	O
data	O
that	O
constantly	O
changes	O
.	O
</s>
<s>
Real-time	B-Application
databases	I-Application
may	O
be	O
modified	O
to	O
improve	O
accuracy	O
and	O
efficiency	O
and	O
to	O
avoid	O
conflict	O
,	O
by	O
providing	O
deadlines	O
and	O
wait	O
periods	O
to	O
insure	O
temporal	O
consistency	O
.	O
</s>
<s>
Real-time	B-Application
database	I-Application
systems	O
offer	O
a	O
way	O
of	O
monitoring	O
a	O
physical	O
system	O
and	O
representing	O
it	O
in	O
data	B-General_Concept
streams	I-General_Concept
to	O
a	O
database	O
.	O
</s>
<s>
A	O
data	B-General_Concept
stream	I-General_Concept
,	O
like	O
memory	O
,	O
fades	O
over	O
time	O
.	O
</s>
<s>
Now	O
database	B-Application
systems	I-Application
are	O
faster	O
than	O
they	O
were	O
in	O
the	O
past	O
.	O
</s>
<s>
In	O
the	O
future	O
,	O
we	O
can	O
look	O
forward	O
to	O
even	O
faster	O
database	B-Application
systems	I-Application
.	O
</s>
<s>
Fast	O
processing	O
that	O
is	O
misapplied	O
is	O
not	O
helpful	O
for	O
real-time	B-Application
database	I-Application
systems	O
.	O
</s>
<s>
In	O
fact	O
,	O
faster	O
processing	O
hurts	O
some	O
real-time	B-General_Concept
applications	I-General_Concept
because	O
increased	O
speed	O
brings	O
more	O
complexity	O
and	O
more	O
of	O
a	O
chance	O
for	O
problems	O
caused	O
by	O
a	O
variance	O
of	O
speed	O
.	O
</s>
<s>
With	O
future	O
database	B-Application
systems	I-Application
running	O
even	O
faster	O
than	O
ever	O
,	O
there	O
is	O
a	O
need	O
to	O
do	O
more	O
studies	O
so	O
we	O
can	O
continue	O
to	O
have	O
efficient	O
systems	O
.	O
</s>
<s>
The	O
amount	O
of	O
research	O
studying	O
real-time	B-Application
database	I-Application
systems	O
will	O
increase	O
because	O
of	O
commercial	O
applications	O
such	O
as	O
web	O
based	O
auction	O
houses	O
like	O
eBay	B-Application
.	I-Application
</s>
<s>
This	O
also	O
enables	O
new	O
technologies	O
such	O
as	O
web-video	O
conferencing	O
and	O
instant	B-Application
messenger	I-Application
conversations	O
in	O
sound	O
and	O
high-resolution	O
video	O
,	O
which	O
are	O
reliant	O
on	O
real-time	B-Application
database	I-Application
systems	O
.	O
</s>
