mirror of https://github.com/apache/druid.git
63 lines
2.6 KiB
Markdown
63 lines
2.6 KiB
Markdown
---
|
|
layout: doc_page
|
|
title: "Cassandra Deep Storage"
|
|
---
|
|
|
|
<!--
|
|
~ Licensed to the Apache Software Foundation (ASF) under one
|
|
~ or more contributor license agreements. See the NOTICE file
|
|
~ distributed with this work for additional information
|
|
~ regarding copyright ownership. The ASF licenses this file
|
|
~ to you under the Apache License, Version 2.0 (the
|
|
~ "License"); you may not use this file except in compliance
|
|
~ with the License. You may obtain a copy of the License at
|
|
~
|
|
~ http://www.apache.org/licenses/LICENSE-2.0
|
|
~
|
|
~ Unless required by applicable law or agreed to in writing,
|
|
~ software distributed under the License is distributed on an
|
|
~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
|
|
~ KIND, either express or implied. See the License for the
|
|
~ specific language governing permissions and limitations
|
|
~ under the License.
|
|
-->
|
|
|
|
# Cassandra Deep Storage
|
|
|
|
## 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](https://github.com/Netflix/astyanax/wiki/Chunked-Object-Store) 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:
|
|
|
|
```sql
|
|
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`](http://www.datastax.com/documentation/cql/3.1/cql/cql_reference/create_keyspace_r.html) command.
|
|
|
|
Then, add the following to your Historical and realtime runtime properties files to enable a Cassandra backend.
|
|
|
|
```properties
|
|
druid.extensions.loadList=["druid-cassandra-storage"]
|
|
druid.storage.type=c*
|
|
druid.storage.host=localhost:9160
|
|
druid.storage.keyspace=druid
|
|
```
|