Database Reference
In-Depth Information
PHI THRESHOLD AND ACCRUAL FAILURE DETECTORS
Since its inception at Facebook, Cassandra has employed what is called an Accrual Failure Detector.
This is a failure detector that outputs a value associated with each process (or node). This value is called
Phi. The value is output in a manner that is designed from the ground up to be adaptive in the face of
volatile network conditions, so it's not a binary condition that simply checks whether a server is up or
down.
The Phi convict threshold in the configuration adjusts the sensitivity of the failure detector. Lower values
increase the sensitivity and higher values decrease it, but not in a linear fashion.
The Phi value refers to a level of suspicionthat a server might be down. Applications such as Cassandra
that employ an AFD can specify variable conditions for the Phi value they emit. Cassandra can generally
detect a failed node in about 10 seconds using this mechanism.
You can read the original Phi Accrual Failure Detection paper on which Cassandra's design is based at
http://ddg.jaist.ac.jp/pub/HDY+04.pdf .
Additional Tools
This section discusses miscellaneous tools that ship with Cassandra to help you configure it.
Viewing Keys
You can see which keys are in your SSTables using a script called sstablekeys . To run it, just
use the location of the SSTable for which you want to see keys, as shown here:
eben@morpheus$ bin/sstablekeys /var/lib/cassandra/data/Hotelier/Hotel-1-Data.db
WARN 10:56:05,928 Schema definitions were defined both locally and in
cassandra.yaml.
Definitions in cassandra.yaml were ignored.
415a435f303433
415a535f303131
4341535f303231
4e594e5f303432
Importing Previous Configurations
If you had a keyspace defined in 0.6 using the configuration file that you'd like to import
into Cassandra 0.7 or higher, you can use a special JMX operation, StorageSer-
vice.loadSchemaFromYaml() . Note that this method has two important caveats: first, it is in-
tended to be used only once; second, it will probably be removed by version 0.8.
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