Event Table Definitions

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

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

Unlike predefined tables, event tables can have sophisticated storage and retrieval criteria. 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 and therefore, are faster and easier to define. Following example shows a definition of 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 as follows:

• • MySQL

  • H2

The following example shows how to define a table with table id cseEventTable. It stores events in a relational database table named cepEventTable.

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

CEP supports caching for relational database tables with a few different algorithms. To change the algorithm, you 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', 'table.name'='cepEventTable', 'caching.algorithm'='LRU')

Optionally, you can define a cache size using cache.size parameter when defining the table as follows:

define table cseEventTable (symbol string, price int, volume float) from ('datasource.name'='cepDataSource', 'table.name'='cepEventTable', 'caching.algorithm'='LRU', 'cache.size'='10000')

In addition, you can also define a relational database event table with a user-provided SQL query as follows. This is 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', 'table.name'='cepEventTable'  'create.query'='CREATE TABLE cepEventTable (symbol VARCHAR(40), price DECIMAL, volume BIGINT )')