13.4. Cassandra Connector

The Cassandra connector allows querying data stored in Cassandra.

Configuration

To configure the Cassandra connector, create a catalog properties file /etc/opt/prestoadmin/connector/cassandra.properties with the following contents, replacing host1,host2 with a comma-separated list of the Cassandra nodes 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 your Cassandra nodes are not using the default port (9042).

Use presto-admin to deploy the connector file. See Adding a Catalog.

Multiple Cassandra Clusters

You can have as many catalogs as you need, so if you have additional Cassandra clusters, simply add another properties file to /etc/opt/prestoadmin/connector with a different name (making sure it ends in .properties). For example, if you name the property file sales.properties, Presto will create a catalog named sales using the configured connector.

Configuration Properties

The following configuration properties are available:

Property Name	Description
`cassandra.contact-points`	Comma-separated list of hosts in a Cassandra cluster. The Cassandra driver will use these contact points to discover cluster topology. At least one Cassandra host is required.
`cassandra.native-protocol-port`	The Cassandra server port running the native client protocol (defaults to `9042`).
`cassandra.thrift-port`	The Cassandra server port running the Thrift client protocol (defaults to `9160`).
`cassandra.limit-for-partition-key-select`	Limit of rows to read for finding all partition keys. If a Cassandra table has more rows than this value, splits based on token ranges are used instead. Note that for larger values you may need to adjust read timeout for Cassandra.
`cassandra.max-schema-refresh-threads`	Maximum number of schema cache refresh threads. This property corresponds to the maximum number of parallel requests.
`cassandra.schema-cache-ttl`	Maximum time that information about a schema will be cached (defaults to `1h`).
`cassandra.schema-refresh-interval`	The schema information cache will be refreshed in the background when accessed if the cached data is at least this old (defaults to `2m`).
`cassandra.consistency-level`	Consistency levels in Cassandra refer to the level of consistency to be used for both read and write operations. More information about consistency levels can be found in the Cassandra consistency documentation. This property defaults to a consistency level of `ONE`. Possible values include `ALL`, `EACH_QUORUM`, `QUORUM`, `LOCAL_QUORUM`, `ONE`, `TWO`, `THREE`, `LOCAL_ONE`, `ANY`, `SERIAL`, `LOCAL_SERIAL`.
`cassandra.allow-drop-table`	Set to `true` to allow dropping Cassandra tables from Presto via DROP TABLE (defaults to `false`).
`cassandra.username`	Username used for authentication to the Cassandra cluster. This is a global setting used for all connections, regardless of the user who is connected to Presto.
`cassandra.password`	Password used for authentication to the Cassandra cluster. This is a global setting used for all connections, regardless of the user who is connected to Presto.

The following advanced configuration properties are available:

Property Name	Description
`cassandra.fetch-size`	Number of rows fetched at a time in a Cassandra query.
`cassandra.fetch-size-for-partition-key-select`	Number of rows fetched at a time in a Cassandra query that selects partition keys.
`cassandra.partition-size-for-batch-select`	Number of partitions batched together into a single select for a single partion key column table.
`cassandra.split-size`	Number of keys per split when querying Cassandra.
`cassandra.partitioner`	Partitioner to use for hashing and data distribution. This property defaults to `Murmur3Partitioner`. The other supported values are `RandomPartitioner` and `ByteOrderedPartitioner`.
`cassandra.thrift-connection-factory-class`	Allows for the specification of a custom implementation of `org.apache.cassandra.thrift.ITransportFactory` to be used to connect to Cassandra using the Thrift protocol.
`cassandra.transport-factory-options`	Allows for the specification of arbitrary options to be passed to the Thrift connection factory.
`cassandra.client.read-timeout`	Maximum time the Cassandra driver will wait for an answer to a query from one Cassandra node. Note that the underlying Cassandra driver may retry a query against more than one node in the event of a read timeout. Increasing this may help with queries that use an index.
`cassandra.client.connect-timeout`	Maximum time the Cassandra driver will wait to establish a connection to a Cassandra node. Increasing this may help with heavily loaded Cassandra clusters.
`cassandra.client.so-linger`	Number of seconds to linger on close if unsent data is queued. If set to zero, the socket will be closed immediately. When this option is non-zero, a socket will linger that many seconds for an acknowledgement that all data was written to a peer. This option can be used to avoid consuming sockets on a Cassandra server by immediately closing connections when they are no longer needed.
`cassandra.retry-policy`	Policy used to retry failed requests to Cassandra. This property defaults to `DEFAULT`. Using `BACKOFF` may help when queries fail with “not enough replicas”. The other possible values are `DOWNGRADING_CONSISTENCY` and `FALLTHROUGH`.
`cassandra.load-policy.use-dc-aware`	Set to `true` to use `DCAwareRoundRobinPolicy` (defaults to `false`).
`cassandra.load-policy.dc-aware.local-dc`	The name of the local datacenter for `DCAwareRoundRobinPolicy`.
`cassandra.load-policy.dc-aware.used-hosts-per-remote-dc`	Uses the provided number of host per remote datacenter as failover for the local hosts for `DCAwareRoundRobinPolicy`.
`cassandra.load-policy.dc-aware.allow-remote-dc-for-local`	Set to `true` to allow to use hosts of remote datacenter for local consistency level.
`cassandra.load-policy.use-token-aware`	Set to `true` to use `TokenAwarePolicy` (defaults to `false`).
`cassandra.load-policy.shuffle-replicas`	Set to `true` to use `TokenAwarePolicy` with shuffling of replicas (defaults to `false`).
`cassandra.load-policy.use-white-list`	Set to `true` to use `WhiteListPolicy` (defaults to `false`).
`cassandra.load-policy.white-list.addresses`	Comma-separated list of hosts for `WhiteListPolicy`.
`cassandra.no-host-available-retry-count`	Retry count for `NoHostAvailableException` (defaults to `1`).

Querying Cassandra Tables

The users table is an example Cassandra table from the Cassandra Getting Started guide. It can be created along with the mykeyspace keyspace 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   | Null | Partition Key | Comment
---------+---------+------+---------------+---------
 user_id | bigint  | true | true          |
 fname   | varchar | true | false         |
 lname   | varchar | true | false         |
(3 rows)

This table can then be queried in Presto:

SELECT * FROM cassandra.mykeyspace.users;