Extensions

Druid implements an extension system that allows for adding functionality at runtime. Extensions are commonly used to add support for deep storage (like HDFS and S3), metadata stores (like MySQL and PostgreSQL), new aggregators, new input formats, and so on.

Production clusters will generally use at least two extensions; one for deep storage and one for a metadata store. Many clusters will also use additional extensions.

Loading extensions

Loading bundled extensions

Imply bundles many commonly used extensions out of the box, including all core Druid extensions. See the list of extensions below for your options. You can load bundled extensions by adding their names to your common.runtime.properties druid.extensions.loadList property. For example, to load the postgresql-metadata-storage and druid-hdfs-storage extensions, use the configuration:

druid.extensions.loadList=["postgresql-metadata-storage", "druid-hdfs-storage"]

Note that Imply bundles two sets of configurations: one for the quickstart and one for a clustered configuration. Make sure you are updating the correct common.runtime.properties for your setup.

Loading community and third-party extensions

You can also install community and third-party extensions not already bundled with the Imply distribution. To do this, first download the extension and then install it into your dist/druid/extensions/ directory. You can download extensions from their distributors directly, or if they are available from Maven, the included pull-deps tool can download them for you. To use pull-deps specify the full Maven coordinate of the extension in the form groupId:artifactId:version.

If you are installing a Druid community-contributed extension, use a coordinate like org.apache.extensions.contrib:druid-orc-extensions:0.13.0-incubating. The version you provide should match the community Druid version that your Imply distribution is based on. For example, to install druid-orc-extension, run:

java \
  -cp "dist/druid/lib/*" \
  -Ddruid.extensions.directory="dist/druid/extensions" \
  -Ddruid.extensions.hadoopDependenciesDir="dist/druid/hadoop-dependencies" \
  org.apache.druid.cli.Main tools pull-deps \
  --no-default-hadoop \
  -c "org.apache.druid.extensions.contrib:druid-orc-extensions:0.13.0-incubating"

Then, add "druid-example-extension" to druid.extensions.loadList in common.runtime.properties to instruct Druid to load the extension.

Community extensions are contributed by Druid community members but are not necessarily maintained on an ongoing basis by Druid committers. The Druid documentation contains a list of community extensions.

Imply does not provide support for community extensions.

List of bundled extensions

The following extensions are bundled with the Imply distribution. To load bundled extensions, see Loading bundled extensions. To install other extensions, see Loading community and third-party extensions.

Druid core extensions

Core extensions are maintained by Druid committers. Some are in experimental status and some are fully production-tested Druid components.

For additional documentation on these extensions, see the Druid documentation.