<s>
In	O
computer	B-General_Concept
programming	I-General_Concept
,	O
primary	B-Algorithm
clustering	I-Algorithm
is	O
one	O
of	O
two	O
major	O
failure	O
modes	O
of	O
open	B-Algorithm
addressing	I-Algorithm
based	O
hash	B-Algorithm
tables	I-Algorithm
,	O
especially	O
those	O
using	O
linear	B-Algorithm
probing	I-Algorithm
.	O
</s>
<s>
It	O
occurs	O
after	O
a	O
hash	B-Algorithm
collision	I-Algorithm
causes	O
two	O
of	O
the	O
records	O
in	O
the	O
hash	B-Algorithm
table	I-Algorithm
to	O
hash	B-Error_Name
to	O
the	O
same	O
position	O
,	O
and	O
causes	O
one	O
of	O
the	O
records	O
to	O
be	O
moved	O
to	O
the	O
next	O
location	O
in	O
its	O
probe	O
sequence	O
.	O
</s>
<s>
Once	O
this	O
happens	O
,	O
the	O
cluster	O
formed	O
by	O
this	O
pair	O
of	O
records	O
is	O
more	O
likely	O
to	O
grow	O
by	O
the	O
addition	O
of	O
even	O
more	O
colliding	O
records	O
,	O
regardless	O
of	O
whether	O
the	O
new	O
records	O
hash	B-Error_Name
to	O
the	O
same	O
location	O
as	O
the	O
first	O
two	O
.	O
</s>
<s>
For	O
instance	O
,	O
in	O
linear	B-Algorithm
probing	I-Algorithm
,	O
a	O
record	O
involved	O
in	O
a	O
collision	O
is	O
always	O
moved	O
to	O
the	O
next	O
available	O
hash	B-Algorithm
table	I-Algorithm
cell	O
subsequent	O
to	O
the	O
position	O
given	O
by	O
its	O
hash	B-Error_Name
function	I-Error_Name
,	O
creating	O
a	O
contiguous	O
cluster	O
of	O
occupied	O
hash	B-Algorithm
table	I-Algorithm
cells	O
.	O
</s>
<s>
Because	O
of	O
this	O
phenomenon	O
,	O
it	O
is	O
likely	O
that	O
a	O
linear-probing	O
hash	B-Algorithm
table	I-Algorithm
with	O
a	O
constant	O
load	O
factor	O
(	O
that	O
is	O
,	O
with	O
the	O
size	O
of	O
the	O
table	O
proportional	O
to	O
the	O
number	O
of	O
items	O
it	O
stores	O
)	O
will	O
have	O
some	O
clusters	O
of	O
logarithmic	O
length	O
,	O
and	O
will	O
take	O
logarithmic	O
time	O
to	O
search	O
for	O
the	O
keys	O
within	O
that	O
cluster	O
.	O
</s>
<s>
A	O
related	O
phenomenon	O
,	O
secondary	O
clustering	O
,	O
occurs	O
more	O
generally	O
with	O
open	B-Algorithm
addressing	I-Algorithm
modes	O
including	O
linear	B-Algorithm
probing	I-Algorithm
and	O
quadratic	B-Algorithm
probing	I-Algorithm
in	O
which	O
the	O
probe	O
sequence	O
is	O
independent	O
of	O
the	O
key	O
,	O
as	O
well	O
as	O
in	O
hash	B-Error_Name
chaining	O
.	O
</s>
<s>
In	O
this	O
phenomenon	O
,	O
a	O
low-quality	O
hash	B-Error_Name
function	I-Error_Name
may	O
cause	O
many	O
keys	O
to	O
hash	B-Error_Name
to	O
the	O
same	O
location	O
,	O
after	O
which	O
they	O
all	O
follow	O
the	O
same	O
probe	O
sequence	O
or	O
are	O
placed	O
in	O
the	O
same	O
hash	B-Error_Name
chain	O
as	O
each	O
other	O
,	O
causing	O
them	O
to	O
have	O
slow	O
access	O
times	O
.	O
</s>
<s>
Both	O
types	O
of	O
clustering	O
may	O
be	O
reduced	O
by	O
using	O
a	O
higher-quality	O
hash	B-Error_Name
function	I-Error_Name
,	O
or	O
by	O
using	O
a	O
hashing	O
method	O
such	O
as	O
double	B-Algorithm
hashing	I-Algorithm
that	O
is	O
less	O
susceptible	O
to	O
clustering	O
.	O
</s>
