- Introduction
- Apache Cassandra is a highly scalable, high-performance distributed database
- It is a column-oriented database
- Its destribution design is based on Amazon’s Dynamo and its data model on Google’s Bigtable
- The design goal of Cassandra is to handle big data workloads across multiple nodes without any single point of failure
- It is NoSQL database
- store and retrieve data other than the tabular relations used in relational databases
- schema-free
- easy replication
- eventually consistent
- can handle huge amounts of data
- Users can access Cassandra through its nodes using Cassandra Query Language (CQL)
- documentation doc
- snitch is how the nodes in a cluster know about the topology of the cluster
- ways to define snitch:
- SimpleSnitch: used with cluster only in one data center
- PropertyFileSnitch: For example 130.77.100.147 =DC1:RAC1; LHS is IP address, RHS is data center number : RAC number
- data distribution is done through consistent hashing, to strive for even distribution of data across the nodes in a cluster
- to distribute the rows across the nodes, a partitioner is used. The partitioner uses an algorithm to determine which node a given row of data will go. The default partitioner in Cassandra is Murmur3.
- Murmur3 takes the value in the first column of the row to generate a unique number between -2^63 and 2^63
- each node also has a value and is responsible for storing the token(data) values between its endpoint and the endpoint of the previous node (the value of each node can be calculated through Murmur 3 calculator)
- A replication factor specifies how many instances of the data there will be within a given database
- Virtual nodes are an alternative way to assign token ranges to nodes and are now the default in Cassandra
- With virtual nodes, insteading of a node being responsible for only one token range, it is instead responsible for many small token ranges (by default, 256 of them).
- One advantage of virtual node is that the computation power of each node is different. Node with powerful computation can take more ranges.
- start cassandra in background mode:
./cassandra
- start cassandra in foreground mode:
./cassandra -f
nodetool status check node status, can get information such as address, load etcnodetool info check the general information of this nodenodetool ring check the token range- CQL (Cassandra Query Language) is a SQL-like query language for communicating with Cassandra.
- Foradministrative activities, such as cluster monitoring and management tasks, tools built on JMX (java management extensions) are commonly used
- Create a database
- a database is defined as a keysapce. Within the keysapce tables can be defined
- in cqlsh, type
describe keyspaces can list all the keyspaces
- type
describe keyspace <name> can list tables in a specific keyspace
- keyspace can be defined/added by
create keysapce <name> with replication = {'class':<strategy>, 'dc1': <number of replica>}. To run locally we can do ```create keyspace with replication = {'class':'SimpleStrategy', 'replication_factor':1}
- delete keyspace:
drop keyspace <name>
- Data Model
- every node has a replica
- keyspace is the outermost container for data in Cassandra. It contains:
- replication factor: determine the number of machines in the cluster that will receive copies of the same data
- replica placement strategy
- column families: represent the structure of your data
- the schema is not fixed. Cassandra does not force individual rows to have all the columns