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.
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The following example shows defining a table with table id 'cseEventTable' which actually stores events in a relational database named 'cepdb' inside a relational database table named 'cepEventTable'.
define table cseEventTable (symbol string, price int, volume float) from ('datasource.name'='cepDataSource', 'database.name'='cepdb', 'table.name'='cepEventTable')
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define table cseEventTable (symbol string, price int, volume float) from ('datasource.name'='cepDataSource', 'database.name'='cepdb', 'table.name'='cepEventTable', 'caching.algorithm'='LRU')
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Currently there are three cache management algorithms supported by CEP. Those are:
Note that specifying an algorithm is optional and when the user doesn't specify an algorithm, the basic algorithm will be used by defaultcaching gets disabled. |
Optionally you can define a cache size when defining the table as follows using 'cache.size' parameter:
define table cseEventTable (symbol string, price int, volume float) from ('datasource.name'='cepDataSource', 'database.name'='cepdb', 'table.name'='cepEventTable', 'caching.algorithm'='LRU', 'cache.size'='10000')
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The 'datasource.name' given here is injected to the Siddhi engine by the WSO2 CEP server. To configure data sources in WSO2 CEP, please refer to the data sources configuration documentation in the Admin Guide. |
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Note that from CEP 3.1.0 onwards, the parameter 'database.name' is not supported. Instead, users are required to create the data source pointing to a specific database which will be used to create the tables. |
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The table id can be different from the table name, and Siddhi will always refer to the table id defined here. However, the table id cannot be same as an already existing stream id, since syntactically both are considered in the same manner in the query language. |