A transformer plugin is a set of go functions that perform specific formatting or processing on data after is read from a Kafka or RabbitMQ data source.
This topic describes transformer plugins and how to use them with Greenplum Streaming Server:
Developing a Transformer Plugin for GPSS
A transformer plugin is a set of go functions. You compile the go functions that you develop into a shared library. Users of the plugin specify the file system path to this library in the GPSS load configuration file.
The GPSS transformer plugin framework exposes two entry points:
- Plugin initialization function - GPSS invokes this function once when it loads the transformer plugin.
- Plugin transform function - GPSS invokes this function for every message it reads from the source.
The framework supports specifying properties that direct the processing performed by the transformer. GPSS passes any transformer properties specified in the load configuration file to the go functions. The transformer-related load configuration properties are described further in Using a Transformer Plugin in GPSS.
Refer to the gp-stream-server-plugin github repository for an example Greenplum Streaming Server transformer plugin implementation.
Using a Transformer Plugin in GPSS
To use a transformer plugin in a Kafka or RabbitMQ data job, you must specify an INPUT:TRANSFORMER (version 2) or sources:<source>:transformer (version 3) block in the load configuration file. The properties in this block identify the file system path to the transformer plugin library, the initialization and transform function names, and transform-specific properties that GPSS passes to the functions.
Version 2 format syntax:
[TRANSFORMER:
PATH: <path_to_plugin_transform_library>
ON_INIT: <plugin_transform_init_name>
TRANSFORM: <plugin_transform_name>
PROPERTIES:
<plugin_transform_property_name>: <property_value>
[ ... ] ]
Version 3 format syntax:
transformer:
path: <path_to_plugin_transform_library>
on_init: <plugin_transform_init_name>
transform: <plugin_transform_name>
properties:
<plugin_transform_property_name>: <property_value>
...
When you specify a transformer plugin in your GPSS load configuration file, GPSS invokes the transform function to process the data after it applies an input filter (if specified).
