Documentation for C*

This commit is contained in:
Brian O'Neill 2013-05-07 16:53:12 -04:00
parent 863b8808cc
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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](https://github.com/Netflix/astyanax/wiki/Chunked-Object-Store) repository. It contains
compressed segments for distribution to real-time and compute 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`)
Then, add the following properties to your properties file to enable a Cassandra
backend.
druid.pusher.cassandra=true
druid.pusher.cassandra.host=localhost:9160
druid.pusher.cassandra.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`.

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{
"queryType": "groupBy",
"dataSource": "appevents",
"granularity": "all",
"dimensions": ["appid", "event"],
"aggregations":[
{"type":"count", "name":"eventcount"},
{"type":"doubleSum", "fieldName":"events", "name":"eventssum"}
],
"intervals":["2012-10-01T00:00/2020-01-01T00"]
}

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);
// Create dummy objects for the various interfaces that interact with the DB, ZK and deep storage
//rn.setSegmentPublisher(new NoopSegmentPublisher());
//rn.setAnnouncer(new NoopDataSegmentAnnouncer());
//rn.setDataSegmentPusher(new NoopDataSegmentPusher());
//rn.setServerView(new NoopServerView());
//rn.setInventoryView(new NoopInventoryView());
rn.setSegmentPublisher(new NoopSegmentPublisher());
rn.setAnnouncer(new NoopDataSegmentAnnouncer());
rn.setDataSegmentPusher(new NoopDataSegmentPusher());
rn.setServerView(new NoopServerView());
rn.setInventoryView(new NoopInventoryView());
Runtime.getRuntime().addShutdownHook(
new Thread(