Database Reference
In-Depth Information
1000 × 1000 cell spreadsheet, similar to a relational table. If many of the cells have empty
values, the storage model is inefficient.
SSTablle
SSTable stands for Sorted String Table. Inherited from Google's Bigtable, an SSTable is how
data is stored on disk in Cassandra. It is a log that allows only appending. In-memory tables
(memtables) are used in front of SSTables for buffering and sorting data. SSTables allow for
high performance on writes and can be compacted.
SSTables are immutable. Once a memtable is flushed to disk as an SSTable, it cannot be
changed by the application;
Compaction
changes only their on-disk representation.
To import or export data from JavaScript Object Notation (JSON), check out the classes
org.apache.cassandra.tools.SSTableImporter
and
SSTableExporter
.
Sttage
Part of Cassandra's Staged Event-Driven Architecture (SEDA), a stagewraps a basic unit of
work. A single operation can flow between various stages to complete, rather than getting
completed in the same thread that started the work.
A stage consists of an incoming event queue, an event handler, and an associated thread
pool. Stages are managed by a controller that determines scheduling and thread allocation;
Cassandra implements this kind of concurrency model using the thread pool
java.util.concurrent.ExecutorService
. To see specifically how this works, check out
the
org.apache.cassandra.concurrent.StageManager
class.
A few additional operations are implemented as stages too, including working with memt-
ables in the
ColumnFamilyStore
class, and the consistency manager is a stage in the
Stor-
ageService
.
An operation may start with one thread, which then hands off the work to another thread,
which may hand it off to other threads. This handing-off is not directly between threads,
however; it occurs between stages.
See also
SEDA (Staged Event-Driven Architecture)
.
Sttrong C
g Consiisttency
For reads, strong consistency means that if it is detected that a repair needs to be made, first
perform the read repair, then return the result.
