6.3. Cassandra Connector

The Cassandra connector allows querying data stored in Cassandra.

Compatibility

Connector is compatible with all Cassandra versions starting from 2.1.5.

Configuration

To configure the Cassandra connector, create a catalog properties fileetc/catalog/cassandra.properties with the following contents,replacing host1,host2 with a comma-separated list of the Cassandranodes used to discovery the cluster topology:

connector.name=cassandra
cassandra.contact-points=host1,host2

You will also need to set cassandra.native-protocol-port if yourCassandra nodes are not using the default port (9042).

Multiple Cassandra Clusters

You can have as many catalogs as you need, so if you have additionalCassandra clusters, simply add another properties file to etc/catalogwith a different name (making sure it ends in .properties). Forexample, if you name the property file sales.properties, Prestowill create a catalog named sales using the configured connector.

Configuration Properties

The following configuration properties are available:

Note

If authorization is enabled, cassandra.username must have enough permissions to perform SELECT queries onthe system.size_estimates table.

The following advanced configuration properties are available:

Querying Cassandra Tables

The users table is an example Cassandra table from the CassandraGetting Started guide. It can be created along with the mykeyspacekeyspace using Cassandra’s cqlsh (CQL interactive terminal):

cqlsh> CREATE KEYSPACE mykeyspace
   ... WITH REPLICATION = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
cqlsh> USE mykeyspace;
cqlsh:mykeyspace> CREATE TABLE users (
              ...   user_id int PRIMARY KEY,
              ...   fname text,
              ...   lname text
              ... );

This table can be described in Presto:

DESCRIBE cassandra.mykeyspace.users;

 Column  |  Type   | Extra | Comment
---------+---------+-------+---------
 user_id | bigint  |       |
 fname   | varchar |       |
 lname   | varchar |       |
(3 rows)

This table can then be queried in Presto:

SELECT * FROM cassandra.mykeyspace.users;

Data types

The data types mappings are as follows:

Any collection (LIST/MAP/SET) can be designated as FROZEN, and the value ismapped to VARCHAR. Additionally, blobs have the limitation that they cannot be empty.

Types not mentioned in the table above are not supported (e.g. tuple or UDT).

Partition keys can only be of the following types:| ASCII| TEXT| VARCHAR| BIGINT| BOOLEAN| DOUBLE| INET| INT| FLOAT| DECIMAL| TIMESTAMP| UUID| TIMEUUID

Limitations

• Queries without filters containing the partition key result in fetching all partitions.This causes a full scan of the entire data set, therefore it’s much slower compared to a similarquery with a partition key as a filter.
• IN list filters are only allowed on index (that is, partition key or clustering key) columns.
• Range (< or > and BETWEEN) filters can be applied only to the partition keys.