Cassandra connector

The Cassandra connector allows querying data stored in Apache Cassandra.

Requirements

To connect to Cassandra, you need:

• Cassandra version 2.2 or higher.
• Network access from the Trino coordinator and workers to Cassandra. Port 9042 is the default port.

Configuration

To configure the Cassandra connector, create a catalog properties file etc/catalog/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
cassandra.load-policy.dc-aware.local-dc=datacenter1

You also need to set cassandra.native-protocol-port, if your Cassandra nodes are not using the default port 9042.

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/catalog with a different name, making sure it ends in .properties. For example, if you name the property file sales.properties, Trino creates 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 uses 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.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	Enables DROP TABLE operations. Defaults tofalse.
cassandra.username	Username used for authentication to the Cassandra cluster. This is a global setting used for all connections, regardless of the user connected to Trino.
cassandra.password	Password used for authentication to the Cassandra cluster. This is a global setting used for all connections, regardless of the user connected to Trino.
cassandra.protocol-version	It is possible to override the protocol version for older Cassandra clusters. By default, the value corresponds to the default protocol version used in the underlying Cassandra java driver. Possible values include V3, V4, V5,V6.

note

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

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.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.splits-per-node	Number of splits per node. By default, the values from thesystem.size_estimates table are used. Only override when connecting to Cassandra versions < 2.1.5, which lacks thesystem.size_estimates table.
cassandra.batch-size	Maximum number of statements to execute in one batch.
cassandra.client.read-timeout	Maximum time the Cassandra driver waits 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 waits 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 lingers 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 andFALLTHROUGH.
cassandra.load-policy.use-dc-aware	Set to true if the load balancing policy requires a local datacenter, defaults to true.
cassandra.load-policy.dc-aware.local-dc	The name of the datacenter considered "local".
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 forDefaultLoadBalancingPolicy.
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 TokenAwarePolicywith shuffling of replicas, defaults to false.
cassandra.load-policy.allowed-addresses	Comma-separated list of hosts to allow.
cassandra.no-host-available-retry-timeout	Retry timeout for AllNodesFailedException, defaults to 1m.
cassandra.speculative-execution.limit	The number of speculative executions. This is disabled by default.
cassandra.speculative-execution.delay	The delay between each speculative execution, defaults to500ms.
cassandra.tls.enabled	Whether TLS security is enabled, defaults tofalse.
cassandra.tls.keystore-path	Path to the PEM or JKS key store.
cassandra.tls.truststore-path	Path to the PEM or JKS trust store.
cassandra.tls.keystore-password	Password for the key store.
cassandra.tls.truststore-password	Password for the trust store.

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 Trino:

DESCRIBE cassandra.mykeyspace.users;

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

This table can then be queried in Trino:

SELECT * FROM cassandra.mykeyspace.users;

Data types

The data types mappings are as follows:

Cassandra	Trino
ASCII	VARCHAR
BIGINT	BIGINT
BLOB	VARBINARY
BOOLEAN	BOOLEAN
DATE	DATE
DECIMAL	DOUBLE
DOUBLE	DOUBLE
FLOAT	REAL
INET	VARCHAR(45)
INT	INTEGER
LIST<?>	VARCHAR
MAP<?, ?>	VARCHAR
SET<?>	VARCHAR
SMALLINT	SMALLINT
TEXT	VARCHAR
TIMESTAMP	TIMESTAMP(3) WITH TIME ZONE
TIMEUUID	UUID
TINYINT	TINYINT
TUPLE	ROW with anonymous fields
UUID	UUID
UDT	ROW with field names
VARCHAR	VARCHAR
VARINT	VARCHAR

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

Types not mentioned in the table above are not supported.

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, and is therefore much slower compared to a similar query 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.

SQL support

The connector provides read and write access to data and metadata in the Cassandra database. In addition to the globally available and read operation statements, the connector supports the following features:

• INSERT
• DELETE see DELETE
• TRUNCATE
• CREATE TABLE
• CREATE TABLE
• DROP TABLE

DROP TABLE

By default, DROP TABLE operations are disabled on Cassandra catalogs. To enable DROP TABLE, set the cassandra.allow-drop-table catalog configuration property to true:

cassandra.allow-drop-table=true

SQL delete limitation

DELETE is only supported if the WHERE clause matches entire partitions.