
292 Large Scale and Big Data
by row key where the row range for a table is dynamically partitioned. Each row
range is called a tablet, which represents the unit of distribution and load balancing.
Thus, reads of short row ranges are efcient and typically require communication
with only a small number of machines. Bigtables can have an unbounded number of
columns that are grouped into sets called column families. These column families
represent the basic unit of access control. Each cell in a Bigtable can contain multiple
versions of the same data that are indexed by their timestamps. Each client can ex-
ibly decide the number of n versions of ...