<s>
A	O
column-oriented	B-General_Concept
DBMS	I-General_Concept
or	O
columnar	O
DBMS	O
is	O
a	O
database	B-Application
management	I-Application
system	I-Application
(	O
DBMS	O
)	O
that	O
stores	O
data	O
tables	O
by	O
column	B-Application
rather	O
than	O
by	O
row	O
.	O
</s>
<s>
Practical	O
use	O
of	O
a	O
column	B-General_Concept
store	I-General_Concept
versus	O
a	O
row	O
store	O
differs	O
little	O
in	O
the	O
relational	O
DBMS	O
world	O
.	O
</s>
<s>
Both	O
columnar	O
and	O
row	O
databases	B-Application
can	O
use	O
traditional	O
database	B-Application
query	I-Application
languages	O
like	O
SQL	O
to	O
load	O
data	O
and	O
perform	O
queries	O
.	O
</s>
<s>
Both	O
row	O
and	O
columnar	B-General_Concept
databases	I-General_Concept
can	O
become	O
the	O
backbone	O
in	O
a	O
system	O
to	O
serve	O
data	O
for	O
common	O
extract	O
,	O
transform	O
,	O
load	O
(	O
ETL	O
)	O
and	O
tools	O
.	O
</s>
<s>
A	O
relational	O
database	B-Application
management	I-Application
system	I-Application
provides	O
data	O
that	O
represents	O
a	O
two-dimensional	O
table	O
of	O
columns	O
and	O
rows	O
.	O
</s>
<s>
In	O
an	O
actual	O
implementation	O
,	O
storage	O
hardware	O
requires	O
the	O
data	O
to	O
be	O
serialized	B-Application
into	O
one	O
form	O
or	O
another	O
.	O
</s>
<s>
The	O
most	O
expensive	O
operations	O
involving	O
hard	B-Device
disks	I-Device
are	O
seeks	O
.	O
</s>
<s>
This	O
is	O
known	O
as	O
locality	B-General_Concept
of	I-General_Concept
reference	I-General_Concept
,	O
and	O
the	O
basic	O
concept	O
appears	O
in	O
a	O
number	O
of	O
different	O
contexts	O
.	O
</s>
<s>
Hard	B-Device
disks	I-Device
are	O
organized	O
into	O
a	O
series	O
of	O
blocks	B-Application
of	O
a	O
fixed	O
size	O
,	O
typically	O
enough	O
to	O
store	O
several	O
rows	O
of	O
the	O
table	O
.	O
</s>
<s>
By	O
organizing	O
the	O
table	O
's	O
data	O
so	O
rows	O
fit	O
within	O
these	O
blocks	B-Application
,	O
and	O
grouping	O
related	O
rows	O
onto	O
sequential	O
blocks	B-Application
,	O
the	O
number	O
of	O
blocks	B-Application
that	O
need	O
to	O
be	O
read	O
or	O
sought	O
is	O
minimized	O
in	O
many	O
cases	O
,	O
along	O
with	O
the	O
number	O
of	O
seeks	O
.	O
</s>
<s>
covers	O
techniques	O
for	O
column-/row	O
hybridization	O
as	O
of	O
2017	O
.	O
</s>
<s>
A	O
common	O
method	O
of	O
storing	O
a	O
table	O
is	O
to	O
serialize	B-Application
each	O
row	O
of	O
data	O
,	O
like	O
this	O
:	O
</s>
<s>
To	O
improve	O
the	O
performance	O
of	O
these	O
sorts	O
of	O
operations	O
(	O
which	O
are	O
very	O
common	O
,	O
and	O
generally	O
the	O
point	O
of	O
using	O
a	O
DBMS	O
)	O
,	O
most	O
DBMSs	O
support	O
the	O
use	O
of	O
database	B-Data_Structure
indexes	I-Data_Structure
,	O
which	O
store	O
all	O
the	O
values	O
from	O
a	O
set	O
of	O
columns	O
along	O
with	O
rowid	O
pointers	O
back	O
into	O
the	O
original	O
table	O
.	O
</s>
<s>
An	O
index	O
on	O
the	O
salary	O
column	B-Application
would	O
look	O
something	O
like	O
this	O
:	O
</s>
<s>
The	O
main	O
reason	O
why	O
indexes	O
dramatically	O
improve	O
performance	O
on	O
large	O
datasets	O
is	O
that	O
database	B-Data_Structure
indexes	I-Data_Structure
on	O
one	O
or	O
more	O
columns	O
are	O
typically	O
sorted	O
by	O
value	O
,	O
which	O
makes	O
range	B-General_Concept
queries	I-General_Concept
operations	O
(	O
like	O
the	O
above	O
"	O
find	O
all	O
records	O
with	O
salaries	O
between	O
40,000	O
and	O
50,000	O
"	O
example	O
)	O
very	O
fast	O
(	O
lower	O
time-complexity	O
)	O
.	O
</s>
<s>
A	O
number	O
of	O
row-oriented	O
databases	B-Application
are	O
designed	O
to	O
fit	O
entirely	O
in	O
RAM	B-Architecture
,	O
an	O
in-memory	B-General_Concept
database	I-General_Concept
.	O
</s>
<s>
Such	O
systems	O
may	O
be	O
therefore	O
simpler	O
and	O
smaller	O
,	O
but	O
can	O
only	O
manage	O
databases	B-Application
that	O
will	O
fit	O
in	O
memory	O
.	O
</s>
<s>
A	O
column-oriented	B-General_Concept
database	I-General_Concept
serializes	B-Application
all	O
of	O
the	O
values	O
of	O
a	O
column	B-Application
together	O
,	O
then	O
the	O
values	O
of	O
the	O
next	O
column	B-Application
,	O
and	O
so	O
on	O
.	O
</s>
<s>
This	O
may	O
cause	O
confusion	O
that	O
can	O
lead	O
to	O
the	O
mistaken	O
belief	O
a	O
column-oriented	O
store	O
"	O
is	O
really	O
just	O
"	O
a	O
row-store	O
with	O
an	O
index	O
on	O
every	O
column	B-Application
.	O
</s>
<s>
In	O
a	O
row-oriented	O
system	O
,	O
indices	O
map	O
column	B-Application
values	O
to	O
rowids	O
,	O
whereas	O
in	O
a	O
column-oriented	O
system	O
,	O
columns	O
map	O
rowids	O
to	O
column	B-Application
values	O
.	O
</s>
<s>
Whether	O
or	O
not	O
a	O
column-oriented	O
system	O
will	O
be	O
more	O
efficient	O
in	O
operation	O
depends	O
heavily	O
on	O
the	O
workload	O
being	O
automated	O
.	O
</s>
<s>
A	O
row-oriented	O
system	O
can	O
retrieve	O
the	O
row	O
in	O
a	O
single	O
disk	O
read	O
,	O
whereas	O
numerous	O
disk	O
operations	O
to	O
collect	O
data	O
from	O
multiple	O
columns	O
are	O
required	O
from	O
a	O
columnar	B-General_Concept
database	I-General_Concept
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
column	B-General_Concept
stores	I-General_Concept
have	O
demonstrated	O
excellent	O
real-world	O
performance	O
in	O
spite	O
of	O
many	O
theoretical	O
disadvantages	O
.	O
</s>
<s>
Partitioning	B-General_Concept
,	O
indexing	B-Data_Structure
,	O
caching	O
,	O
views	O
,	O
OLAP	B-Application
cubes	O
,	O
and	O
transactional	O
systems	O
such	O
as	O
write-ahead	B-Algorithm
logging	I-Algorithm
or	O
multiversion	B-Operating_System
concurrency	I-Operating_System
control	I-Operating_System
all	O
dramatically	O
affect	O
the	O
physical	O
organization	O
of	O
either	O
system	O
.	O
</s>
<s>
That	O
said	O
,	O
online	B-General_Concept
transaction	I-General_Concept
processing	I-General_Concept
(	O
OLTP	B-General_Concept
)	O
-focused	O
RDBMS	O
systems	O
are	O
more	O
row-oriented	O
,	O
while	O
online	B-Application
analytical	I-Application
processing	I-Application
(	O
OLAP	B-Application
)	O
-focused	O
systems	O
are	O
a	O
balance	O
of	O
row-oriented	O
and	O
column-oriented	O
.	O
</s>
<s>
Comparisons	O
between	O
row-oriented	O
and	O
column-oriented	B-General_Concept
databases	I-General_Concept
are	O
typically	O
concerned	O
with	O
the	O
efficiency	O
of	O
hard-disk	B-Device
access	O
for	O
a	O
given	O
workload	O
,	O
as	O
seek	O
time	O
is	O
incredibly	O
long	O
compared	O
to	O
the	O
other	O
bottlenecks	O
in	O
computers	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
typical	O
Serial	O
ATA	O
(	O
SATA	O
)	O
hard	B-Device
drive	I-Device
has	O
an	O
average	O
seek	O
time	O
of	O
between	O
16	O
and	O
22	O
milliseconds	O
while	O
DRAM	O
access	O
on	O
an	O
Intel	O
Core	O
i7	O
processor	O
takes	O
on	O
average	O
60	O
nanoseconds	O
,	O
nearly	O
400,000	O
times	O
as	O
fast	O
.	O
</s>
<s>
Columnar	B-General_Concept
databases	I-General_Concept
boost	O
performance	O
by	O
reducing	O
the	O
amount	O
of	O
data	O
that	O
needs	O
to	O
be	O
read	O
from	O
disk	O
,	O
both	O
by	O
efficiently	O
compressing	O
the	O
similar	O
columnar	O
data	O
and	O
by	O
reading	O
only	O
the	O
data	O
necessary	O
to	O
answer	O
the	O
query	O
.	O
</s>
<s>
In	O
practice	O
,	O
columnar	B-General_Concept
databases	I-General_Concept
are	O
well-suited	O
for	O
OLAP-like	O
workloads	O
(	O
e.g.	O
,	O
data	O
warehouses	O
)	O
which	O
typically	O
involve	O
highly	O
complex	O
queries	O
over	O
all	O
data	O
(	O
possibly	O
petabytes	O
)	O
.	O
</s>
<s>
However	O
,	O
some	O
work	O
must	O
be	O
done	O
to	O
write	O
data	O
into	O
a	O
columnar	B-General_Concept
database	I-General_Concept
.	O
</s>
<s>
Transactions	O
(	O
INSERTs	O
)	O
must	O
be	O
separated	O
into	O
columns	O
and	O
compressed	O
as	O
they	O
are	O
stored	O
,	O
making	O
it	O
less	O
suited	O
for	O
OLTP	B-General_Concept
workloads	O
.	O
</s>
<s>
Row-oriented	O
databases	B-Application
are	O
well-suited	O
for	O
OLTP-like	O
workloads	O
which	O
are	O
more	O
heavily	O
loaded	O
with	O
interactive	O
transactions	O
.	O
</s>
<s>
However	O
,	O
column-oriented	O
systems	O
have	O
been	O
developed	O
as	O
hybrids	O
capable	O
of	O
both	O
OLTP	B-General_Concept
and	O
OLAP	B-Application
operations	O
.	O
</s>
<s>
Some	O
of	O
the	O
OLTP	B-General_Concept
constraints	O
,	O
faced	O
by	O
such	O
column-oriented	O
systems	O
,	O
are	O
mediated	O
using	O
(	O
amongst	O
other	O
qualities	O
)	O
in-memory	B-General_Concept
data	O
storage	O
.	O
</s>
<s>
Column-oriented	O
systems	O
suitable	O
for	O
both	O
OLAP	B-Application
and	O
OLTP	B-General_Concept
roles	O
effectively	O
reduce	O
the	O
total	O
data	O
footprint	O
by	O
removing	O
the	O
need	O
for	O
separate	O
systems	O
.	O
</s>
<s>
Column	B-Application
data	O
is	O
of	O
uniform	O
type	O
;	O
therefore	O
,	O
there	O
are	O
some	O
opportunities	O
for	O
storage	O
size	O
optimizations	O
available	O
in	O
column-oriented	O
data	O
that	O
are	O
not	O
available	O
in	O
row-oriented	O
data	O
.	O
</s>
<s>
For	O
example	O
,	O
many	O
popular	O
modern	O
compression	O
schemes	O
,	O
such	O
as	O
LZW	B-Algorithm
or	O
run-length	B-Algorithm
encoding	I-Algorithm
,	O
make	O
use	O
of	O
the	O
similarity	O
of	O
adjacent	O
data	O
to	O
compress	O
.	O
</s>
<s>
For	O
example	O
,	O
using	O
bitmap	B-Data_Structure
indexes	I-Data_Structure
,	O
sorting	O
can	O
improve	O
compression	O
by	O
an	O
order	O
of	O
magnitude	O
.	O
</s>
<s>
To	O
maximize	O
the	O
compression	O
benefits	O
of	O
the	O
lexicographical	O
order	O
with	O
respect	O
to	O
run-length	B-Algorithm
encoding	I-Algorithm
,	O
it	O
is	O
best	O
to	O
use	O
low-cardinality	O
columns	O
as	O
the	O
first	O
sort	O
keys	O
.	O
</s>
<s>
For	O
example	O
,	O
given	O
a	O
table	O
with	O
columns	O
sex	O
,	O
age	O
,	O
name	O
,	O
it	O
would	O
be	O
best	O
to	O
sort	O
first	O
on	O
the	O
value	O
sex	O
(	O
cardinality	B-Application
of	O
two	O
)	O
,	O
then	O
age	O
(	O
cardinality	B-Application
of	O
<	O
128	O
)	O
,	O
then	O
name	O
.	O
</s>
<s>
Therefore	O
,	O
column-oriented	O
architectures	O
are	O
sometimes	O
enriched	O
by	O
additional	O
mechanisms	O
aimed	O
at	O
minimizing	O
the	O
need	O
for	O
access	O
to	O
compressed	O
data	O
.	O
</s>
<s>
Column	B-General_Concept
stores	I-General_Concept
or	O
transposed	O
files	O
have	O
been	O
implemented	O
from	O
the	O
early	O
days	O
of	O
DBMS	O
development	O
.	O
</s>
<s>
TAXIR	O
was	O
the	O
first	O
application	O
of	O
a	O
column-oriented	B-General_Concept
database	I-General_Concept
storage	O
system	O
with	O
focus	O
on	O
information-retrieval	O
in	O
biology	O
in	O
1969	O
.	O
</s>
<s>
Clinical	O
data	O
from	O
patient	O
records	O
with	O
many	O
more	O
attributes	O
than	O
could	O
be	O
analyzed	O
were	O
processed	O
in	O
1975	O
and	O
after	O
by	O
a	O
time-oriented	O
database	B-Application
system	I-Application
(	O
TODS	O
)	O
.	O
</s>
<s>
Another	O
column-oriented	B-General_Concept
database	I-General_Concept
was	O
SCSS	O
.	O
</s>
<s>
Later	O
column-oriented	B-General_Concept
database	I-General_Concept
packages	O
included	O
:	O
</s>
<s>
MonetDB	B-Application
was	O
released	O
under	O
an	O
open-source	O
license	O
on	O
September	O
30	O
,	O
2004	O
,	O
followed	O
closely	O
by	O
the	O
now	O
defunct	O
C-Store	O
.	O
</s>
<s>
The	O
MonetDB-related	O
X100	O
project	O
evolved	O
into	O
VectorWise	B-Application
.	O
</s>
<s>
Druid	B-Application
is	O
a	O
column-oriented	O
data	O
store	O
that	O
was	O
open-sourced	O
in	O
late	O
2012	O
and	O
is	O
now	O
used	O
by	O
numerous	O
organizations	O
.	O
</s>
<s>
Classic	O
Relational	O
DBMS	O
can	O
use	O
column-oriented	O
strategies	O
by	O
mixing	O
row-oriented	O
and	O
column-oriented	O
tables	O
.	O
</s>
<s>
For	O
example	O
in	O
2014	O
Citusdata	O
introduced	O
column-oriented	O
tables	O
for	O
PostgreSQL	B-Application
and	O
McObject	O
added	O
support	O
for	O
columnar	O
storage	O
with	O
its	O
release	O
of	O
eXtremeDB	B-Application
Financial	O
Edition	O
in	O
2012	O
which	O
was	O
then	O
used	O
to	O
establish	O
a	O
new	O
standard	O
of	O
performance	O
for	O
the	O
independently	O
audited	O
STAC-M3	O
benchmark	O
.	O
</s>
