<s>
In	O
computing	O
,	O
a	O
DBM	B-General_Concept
is	O
a	O
library	B-Library
and	O
file	O
format	O
providing	O
fast	O
,	O
single-keyed	O
access	O
to	O
data	O
.	O
</s>
<s>
A	O
key-value	B-Data_Structure
database	I-Data_Structure
from	O
the	O
original	O
Unix	B-Application
,	O
dbm	B-General_Concept
is	O
an	O
early	O
example	O
of	O
a	O
NoSQL	B-General_Concept
system	O
.	O
</s>
<s>
The	O
original	O
dbm	B-General_Concept
library	B-Library
and	O
file	O
format	O
was	O
a	O
simple	O
database	B-General_Concept
engine	I-General_Concept
,	O
originally	O
written	O
by	O
Ken	O
Thompson	O
and	O
released	O
by	O
AT&T	O
in	O
1979	O
.	O
</s>
<s>
The	O
name	O
is	O
a	O
three	O
letter	O
acronym	O
for	O
DataBase	O
Manager	O
,	O
and	O
can	O
also	O
refer	O
to	O
the	O
family	O
of	O
database	B-General_Concept
engines	I-General_Concept
with	O
APIs	O
and	O
features	O
derived	O
from	O
the	O
original	O
dbm	B-General_Concept
.	O
</s>
<s>
The	O
dbm	B-General_Concept
library	B-Library
stores	O
arbitrary	O
data	O
by	O
use	O
of	O
a	O
single	O
key	O
(	O
a	O
primary	B-Application
key	I-Application
)	O
in	O
fixed-size	O
buckets	O
and	O
uses	O
hashing	B-Error_Name
techniques	O
to	O
enable	O
fast	O
retrieval	O
of	O
the	O
data	O
by	O
key	O
.	O
</s>
<s>
The	O
hashing	B-Error_Name
scheme	O
used	O
is	O
a	O
form	O
of	O
extendible	B-Algorithm
hashing	I-Algorithm
,	O
so	O
that	O
the	O
hashing	B-Error_Name
scheme	O
expands	O
as	O
new	O
buckets	O
are	O
added	O
to	O
the	O
database	O
,	O
meaning	O
that	O
,	O
when	O
nearly	O
empty	O
,	O
the	O
database	O
starts	O
with	O
one	O
bucket	O
,	O
which	O
is	O
then	O
split	O
when	O
it	O
becomes	O
full	O
.	O
</s>
<s>
The	O
dbm	B-General_Concept
library	B-Library
and	O
its	O
derivatives	O
are	O
pre-relational	O
databases	O
they	O
manage	O
associative	B-Application
arrays	I-Application
,	O
implemented	O
as	O
on-disk	O
hash	B-Algorithm
tables	I-Algorithm
.	O
</s>
<s>
An	O
agent	O
daemon	B-Operating_System
can	O
handle	O
requests	O
from	O
multiple	O
processes	O
,	O
but	O
introduces	O
IPC	B-Operating_System
overhead	O
.	O
</s>
<s>
The	O
original	O
AT&T	O
dbm	B-General_Concept
library	B-Library
has	O
been	O
replaced	O
by	O
its	O
many	O
successor	O
implementations	O
.	O
</s>
<s>
ndbm	O
(	O
"	O
new	O
dbm	B-General_Concept
"	O
)	O
,	O
based	O
on	O
the	O
original	O
dbm	B-General_Concept
with	O
some	O
new	O
features	O
.	O
</s>
<s>
(	O
"	O
GNU	B-General_Concept
dbm	I-General_Concept
"	O
)	O
,	O
GNU	B-Operating_System
rewrite	O
of	O
the	O
library	B-Library
implementing	O
ndbm	O
features	O
and	O
its	O
own	O
interface	O
.	O
</s>
<s>
sdbm	B-General_Concept
(	O
"	O
small	O
dbm	B-General_Concept
"	O
)	O
,	O
a	O
public	O
domain	O
rewrite	O
of	O
dbm	B-General_Concept
.	O
</s>
<s>
It	O
is	O
a	O
part	O
of	O
the	O
standard	O
distribution	O
for	O
Perl	B-Language
and	O
is	O
available	O
as	O
an	O
external	O
library	B-Library
for	O
Ruby	O
.	O
</s>
<s>
qdbm	B-General_Concept
(	O
"	O
Quick	O
Database	O
Manager	O
"	O
)	O
,	O
a	O
higher-performance	O
dbm	B-General_Concept
employing	O
many	O
of	O
the	O
same	O
techniques	O
as	O
Tokyo/Kyoto	O
Cabinet	O
.	O
</s>
<s>
tdb	O
(	O
"	O
Trivial	B-General_Concept
Database	I-General_Concept
"	O
)	O
,	O
a	O
simple	O
database	O
used	O
by	O
Samba	B-Language
that	O
supports	O
multiple	O
writers	O
.	O
</s>
<s>
Has	O
a	O
gdbm-based	O
API	O
.	O
</s>
<s>
Berkeley	B-Language
DB	I-Language
,	O
1991	O
replacement	O
of	O
ndbm	O
by	O
Sleepycat	O
Software	O
(	O
now	O
Oracle	B-Application
)	O
created	O
to	O
get	O
around	O
the	O
AT&T	O
Unix	B-Application
copyright	O
on	O
BSD	B-Operating_System
.	O
</s>
<s>
It	O
features	O
many	O
extensions	O
like	O
parallelism	O
,	O
transactional	O
control	O
,	O
hashing	B-Error_Name
,	O
and	O
B	O
tree	O
storage	O
.	O
</s>
<s>
LMDB	B-Language
:	O
copy-on-write	B-Language
memory-mapped	B-General_Concept
B+	O
tree	O
implementation	O
in	O
C	B-Language
with	O
a	O
Berkeley-style	O
API	O
.	O
</s>
<s>
The	O
following	O
databases	O
are	O
dbm-inspired	O
,	O
but	O
they	O
do	O
not	O
directly	O
provide	O
a	O
dbm	B-General_Concept
interface	O
,	O
even	O
though	O
it	O
would	O
be	O
trivial	O
to	O
wrap	O
one	O
:	O
</s>
<s>
WiredTiger	B-Application
:	O
database	O
with	O
traditional	O
row-oriented	O
and	O
column-oriented	O
storage	O
.	O
</s>
<s>
As	O
of	O
2001	O
,	O
the	O
ndbm	O
implementation	O
of	O
DBM	B-General_Concept
was	O
standard	O
on	O
Solaris	O
and	O
IRIX	O
,	O
whereas	O
gdbm	B-General_Concept
is	O
ubiquitous	O
on	O
Linux	B-Application
.	O
</s>
<s>
The	O
Berkeley	B-Language
DB	I-Language
implementations	O
were	O
standard	O
on	O
some	O
free	O
operating	O
systems	O
.	O
</s>
<s>
After	O
a	O
change	O
of	O
licensing	O
of	O
the	O
Berkeley	B-Language
DB	I-Language
to	O
GNU	B-Application
AGPL	I-Application
in	O
2013	O
,	O
projects	O
like	O
Debian	O
have	O
moved	O
to	O
LMDB	B-Language
.	O
</s>
<s>
A	O
2018	O
AFL	B-Application
fuzzing	O
test	O
against	O
many	O
DBM-family	O
databases	O
exposed	O
many	O
problems	O
in	O
implementations	O
when	O
it	O
comes	O
to	O
corrupt	O
or	O
invalid	O
database	O
files	O
.	O
</s>
<s>
The	O
authors	O
of	O
gdbm	B-General_Concept
,	O
tdb	O
,	O
and	O
lmdb	B-Language
were	O
prompt	O
to	O
respond	O
.	O
</s>
<s>
Berkeley	B-Language
DB	I-Language
fell	O
behind	O
due	O
to	O
the	O
sheer	O
amount	O
of	O
other	O
issues	O
;	O
the	O
fixes	O
would	O
be	O
irrelevant	O
to	O
open-source	O
software	O
users	O
due	O
to	O
the	O
licensing	O
change	O
locking	O
them	O
back	O
on	O
an	O
old	O
version	O
.	O
</s>
