Example Druid Extension

This is an example project demonstrating how to write a Druid extension. It includes:

• ExampleExtractionFn, an extraction function.
• ExampleSumAggregatorFactory (and related files), an aggregator.
• ExampleByteBufferInputRowParser, an InputRowParser implementation.
• ExampleExtensionModule, the class that registers these with Druid's extension system.
• META-INF/services/org.apache.druid.initialization.DruidModule entry for ExampleExtensionModule.

It also includes unit tests for the above.

You can extend Druid with custom aggregators, query types, filters, and many more as well.

Build

To build the extension, run mvn package and you'll get a file in target like this:

[INFO] Building tar: /src/druid-example-extension/target/druid-example-extension-0.13.0_1-SNAPSHOT-bin.tar.gz
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4.841 s
[INFO] Finished at: 2045-11-04T20:00:53Z
[INFO] Final Memory: 21M/402M
[INFO] ------------------------------------------------------------------------

Unpack the tar.gz and you'll find a directory named druid-example-extension inside it:

$ tar xzf target/druid-example-extension-0.13.0_1-SNAPSHOT-bin.tar.gz
$ ls druid-example-extension-0.10.0_1-SNAPSHOT/
LICENSE                  README.md                druid-example-extension/

Install

To install the extension:

1. Copy druid-example-extension into your Druid extensions directory.
2. Edit conf/_common/common.runtime.properties to add "druid-example-extension" to druid.extensions.loadList. (Edit conf-quickstart/_common/common.runtime.properties too if you are using the quickstart config.) It should look like: druid.extensions.loadList=["druid-example-extension"]. There may be a few other extensions there too.
3. Restart Druid.

Use

ExampleExtractionFn

To use the example extractionFn, call it like a normal extractionFn with type "example", e.g. in a topN. It returns the first "length" characters of each value.

{
  "queryType": "topN",
  "dataSource": "wikiticker",
  "intervals": [
    "2016-06-27/2016-06-28"
  ],
  "granularity": "all",
  "dimension": {
    "type": "extraction",
    "dimension": "page",
    "outputName": "page",
    "extractionFn": {
      "type": "example",
      "length": 5
    }
  },
  "metric": "edits",
  "threshold": 25,
  "aggregations": [
    {
      "type": "longSum",
      "name": "edits",
      "fieldName": "count"
    }
  ]
}

ExampleAggregator

To use the example aggregator, use the type "exampleSum". It does the same thing as the built-in "doubleSum" aggregator.

ExampleSumSqlAggregator

Provides the sql binding for a user defined function. In this case, binding for example_sum making use of the ExampleSumAggregatorFactory. By configuring this binding, a sql query with example_sum can be converted to a native query.

usage - select example_sum('column') from "table"

ExampleByteBufferInputRowParser

The ExampleByteBufferInputRowParser illustrates how an extension can to do a custom transformation of binary input data during indexing. This example extension translates rot13 encoded base64 binary data into Strings, which can then be transformed into a Map by any ParseSpec that that implements a string parser, e.g. json, csv, tsv, and so on.

{
  "type": "kafka",
  "dataSchema": {
    "dataSource": "example-dataset",
    "parser": {
      "type": "exampleParser",
      "parseSpec": {
        "format": "json",
        "timestampSpec": {
          "column": "timestamp",
          "format": "auto"
        },
        "dimensionsSpec": {
          "dimensions": []
        }
      }
    },
    "metricsSpec": [
      {
        "name": "count",
        "type": "count"
      }
    ],
    "granularitySpec": {
      "type": "uniform",
      "segmentGranularity": "HOUR",
      "queryGranularity": "NONE"
    }
  },
  "tuningConfig": {
    "type": "kafka",
    "maxRowsPerSegment": 5000000
  },
  "ioConfig": {
    "topic": "rot13base64json",
    "consumerProperties": {
      "bootstrap.servers": "localhost:9092"
    },
    "taskCount": 1,
    "replicas": 1,
    "taskDuration": "PT1H"
  }
}