Event Table Definitions

define table <table-id> (<attribute-name> <type> {, <attribute-name> <type>}*)
{  from ('parameterName'='value')+ }?  

Event tables allow users to store, retrieve and  process events in a database table-like structure. These are designed for use cases where events need to be extracted from the stream and accumulated over a long period for real-time or later batch processing, such as performing comparisons with the incoming event stream or feeding them to BAM. 

Unlike in windows which are predefined, event tables can have more sophisticated storage and retrieval criteria and a single event table can be used in multiple SiddhiQL expressions.   Depending on the requirements, an event table can be defined either in-memory or in a relational database.  CEP supports event tables for widely used databases such as MySQL.

In Memory Database Event Tables

These are created in memory which will be fast and easier to define. Following example shows a definition for an in memory event table.

define table cseEventTable (symbol string, price int, volume float);

Relational Database Event Tables

Two types of relational databases are currently supported by Siddhi.

• • MySQL

  • H2

The following example shows defining a table with table id 'cseEventTable' which actually stores events in a relational database named 'cepdb' inside a table named 'cepEventTable'. 

define table cseEventTable (symbol string, price int, volume float) from ('datasource.name'='cepDataSource', 'database.name'='cepdb', 'table.name'='cepEventTable')

CEP supports caching for relational database tables with a few different algorithms. To change the algorithm, the users can use the optional 'caching.algorithm' parameter when defining the table as follows:

define table cseEventTable (symbol string, price int, volume float) from ('datasource.name'='cepDataSource', 'database.name'='cepdb', 'table.name'='cepEventTable', 'caching.algorithm'='LRU')

In addition, it is also possible to define a relational database event table with a user-provided SQL query as follows. This can be used when the created table needs to be customized, such as having a primary key etc.

define table cseEventTable (symbol string, price int, volume float) from ('datasource.name'='cepDataSource', 'database.name'='cepdb', 'table.name'='cepEventTable'  'create.query'='CREATE TABLE cepEventTable (symbol VARCHAR(40), price DECIMAL, volume BIGINT )')