mirror of https://github.com/apache/druid.git
45 lines
1.9 KiB
Markdown
45 lines
1.9 KiB
Markdown
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---
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layout: doc_page
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---
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## Introduction
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Druid can use Cassandra as a deep storage mechanism. Segments and their metadata are stored in Cassandra in two tables:
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`index_storage` and `descriptor_storage`. Underneath the hood, the Cassandra integration leverages Astyanax. The
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index storage table is a [Chunked Object](https://github.com/Netflix/astyanax/wiki/Chunked-Object-Store) repository. It contains
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compressed segments for distribution to historical nodes. Since segments can be large, the Chunked Object storage allows the integration to multi-thread
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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
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stores the segment metadatak.
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## Schema
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Below are the create statements for each:
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```sql
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CREATE TABLE index_storage(key text,
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chunk text,
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value blob,
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PRIMARY KEY (key, chunk)) WITH COMPACT STORAGE;
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CREATE TABLE descriptor_storage(key varchar,
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lastModified timestamp,
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descriptor varchar,
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PRIMARY KEY (key)) WITH COMPACT STORAGE;
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```
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## Getting Started
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First create the schema above. I use a new keyspace called `druid` for this purpose, which can be created using the
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[Cassandra CQL `CREATE KEYSPACE`](http://www.datastax.com/documentation/cql/3.1/cql/cql_reference/create_keyspace_r.html) command.
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Then, add the following to your historical and realtime runtime properties files to enable a Cassandra backend.
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```properties
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druid.extensions.coordinates=["io.druid.extensions:druid-cassandra-storage:<druid version>"]
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druid.storage.type=c*
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druid.storage.host=localhost:9160
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druid.storage.keyspace=druid
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```
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Use the `druid-development@googlegroups.com` mailing list if you have questions,
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or feel free to reach out directly: `bone@alumni.brown.edu`.
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