<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
the	O
log-structured	B-Data_Structure
merge-tree	I-Data_Structure
(	O
also	O
known	O
as	O
LSM	O
tree	O
,	O
or	O
LSMT	O
)	O
is	O
a	O
data	B-General_Concept
structure	I-General_Concept
with	O
performance	O
characteristics	O
that	O
make	O
it	O
attractive	O
for	O
providing	O
indexed	B-Data_Structure
access	O
to	O
files	O
with	O
high	O
insert	O
volume	O
,	O
such	O
as	O
transactional	B-General_Concept
log	I-General_Concept
data	I-General_Concept
.	O
</s>
<s>
LSM	O
trees	O
,	O
like	O
other	O
search	B-Data_Structure
trees	I-Data_Structure
,	O
maintain	O
key-value	O
pairs	O
.	O
</s>
<s>
As	O
described	O
by	O
Patrick	O
O'Neil	O
,	O
a	O
two-level	O
LSM	O
tree	O
comprises	O
two	O
tree-like	B-Application
structures	O
,	O
called	O
C0	O
and	O
C1	O
.	O
</s>
<s>
The	O
performance	O
characteristics	O
of	O
LSM	O
trees	O
stem	O
from	O
the	O
fact	O
that	O
each	O
component	O
is	O
tuned	O
to	O
the	O
characteristics	O
of	O
its	O
underlying	O
storage	O
medium	O
,	O
and	O
that	O
data	O
is	O
efficiently	O
migrated	O
across	O
media	O
in	O
rolling	O
batches	O
,	O
using	O
an	O
algorithm	O
reminiscent	O
of	O
merge	B-Algorithm
sort	I-Algorithm
.	O
</s>
<s>
For	O
example	O
,	O
in	O
Apache	B-Application
Cassandra	I-Application
,	O
each	O
value	O
represents	O
a	O
row	O
in	O
a	O
database	O
,	O
and	O
different	O
versions	O
of	O
the	O
row	O
may	O
have	O
different	O
sets	O
of	O
columns	O
.	O
</s>
<s>
LSM-tree	B-Data_Structure
was	O
originally	O
designed	O
for	O
write-intensive	O
workloads	O
.	O
</s>
<s>
As	O
increasingly	O
more	O
read	O
and	O
write	O
workloads	O
co-exist	O
under	O
an	O
LSM-tree	B-Data_Structure
storage	O
structure	O
,	O
read	O
data	O
accesses	O
can	O
experience	O
high	O
latency	O
and	O
low	O
throughput	O
due	O
to	O
frequent	O
invalidations	O
of	O
cached	O
data	O
in	O
buffer	O
caches	O
by	O
LSM-tree	B-Data_Structure
compaction	O
operations	O
.	O
</s>
<s>
LSM	O
trees	O
are	O
used	O
in	O
data	O
stores	O
such	O
as	O
,	O
Bigtable	B-Application
,	O
HBase	B-Language
,	O
LevelDB	B-Language
,	O
Apache	B-Language
Accumulo	I-Language
,	O
SQLite4	B-Language
,	O
Tarantool	B-Operating_System
,	O
RocksDB	B-Language
,	O
WiredTiger	B-Application
,	O
Apache	B-Application
Cassandra	I-Application
,	O
InfluxDB	B-Language
,	O
YugabyteDB	B-Operating_System
,	O
ScyllaDB	B-Language
,	O
and	O
CockroachDB	B-Operating_System
.	O
</s>
