71b8db631c
Updates the required properties to enable Cassandra as deep storage. Also adds more information about how to create the required keystore, and which properties files need to be modified to support Cassandra. Also adds syntax highlighting to the provided example code. Additionally, moves Cassandra Deep Storage documentation out into the actual documentation hierarchy with appropriate linkage. A stub README.md is left in the example directory to provide a useful landing page for existing weblinks to the original documentation.
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Introduction
Druid can use Cassandra as a deep storage mechanism. Segments and their metadata are stored in Cassandra in two tables:
index_storage and descriptor_storage. Underneath the hood, the Cassandra integration leverages Astyanax. The
index storage table is a Chunked Object repository. It contains
compressed segments for distribution to historical nodes. Since segments can be large, the Chunked Object storage allows the integration to multi-thread
the write to Cassandra, and spreads the data across all the nodes in a cluster. The descriptor storage table is a normal C* table that
stores the segment metadatak.
Schema
Below are the create statements for each:
CREATE TABLE index_storage(key text,
chunk text,
value blob,
PRIMARY KEY (key, chunk)) WITH COMPACT STORAGE;
CREATE TABLE descriptor_storage(key varchar,
lastModified timestamp,
descriptor varchar,
PRIMARY KEY (key)) WITH COMPACT STORAGE;
Getting Started
First create the schema above. I use a new keyspace called druid for this purpose, which can be created using the
Cassandra CQL CREATE KEYSPACE command.
Then, add the following to your historical and realtime runtime properties files to enable a Cassandra backend.
druid.extensions.coordinates=["io.druid.extensions:druid-cassandra-storage:<druid version>"]
druid.storage.type=c*
druid.storage.host=localhost:9160
druid.storage.keyspace=druid
Use the druid-development@googlegroups.com mailing list if you have questions,
or feel free to reach out directly: bone@alumni.brown.edu.