Within the filter() function that must be defined within the JavaScript filter, a single event object is supplied as the only argument. That event object contains all of the information about a single event as recorded within the THL as part of the replication process. Each event contains metadata information that can be used to identify or control the content, and individual statement and row data that contain the database changes.

The content of the information is a compound set of data that contains one or more further blocks of data changes, which in turn contains one or more blocks of SQL statements or row data. These blocks are defined using the Java objects that describe their internal format, and are exposed within the JavaScript wrapper as JavaScript objects, that can be parsed and manipulated.

At the top level, the Java object provided to the to the filter() function as the event argument is ReplDBMSEvent. The ReplDBMSEvent class provides the core event information with additional management metadata such as the global transaction ID (seqno), latency of the event and sharding information.

That object contains one or more DBMSData objects. Each DBMSData object contains either a StatementData object (in the case of a statement based event), or a RowChangeData object (in the case of row-based events). For row-based events, there will be one or more OneRowChange objects for each individual row that was changed.

When processing the event information, the data that is processed is live and should be updated in place. For example, when examining statement data, the statement needs only be updated in place, not re-submitted. Statements and rows can also be explicitly removed or added by deleting or extending the arrays that make up the objects.

A basic diagram of the structure is shown in the diagram below:

A single event can contain both statement and row change information within the list of individual DBMSData events. An event or