Cassandra коннектор#

Примечание

Ниже приведена оригинальная документация Trino. Скоро мы ее переведем на русский язык и дополним полезными примерами.

The Cassandra connector allows querying data stored in Apache Cassandra.

Требования#

To connect to Cassandra, you need:

Cassandra version 3.0 or higher.
Network access from the Trino coordinator and workers to Cassandra. Port 9042 is the default port.

Конфигурация#

To configure the Cassandra connector, create a catalog properties file etc/catalog/example.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 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 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`.

Примечание

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 the `system.size_estimates` table are used. Only override when connecting to Cassandra versions < 2.1.5, which lacks the `system.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` and `FALLTHROUGH`.
`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 for `DefaultLoadBalancingPolicy`.
`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.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 to `500ms`.
`cassandra.tls.enabled`	Whether TLS security is enabled, defaults to `false`.
`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 example_keyspace keyspace using Cassandra’s cqlsh (CQL interactive terminal):

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

This table can be described in Trino:

DESCRIBE example.example_keyspace.users;

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

This table can then be queried in Trino:

SELECT * FROM example.example_keyspace.users;

Type mapping#

Because Trino and Cassandra each support types that the other does not, this connector modifies some types when reading or writing data. Data types may not map the same way in both directions between Trino and the data source. Refer to the following sections for type mapping in each direction.

Cassandra type to Trino type mapping#

The connector maps Cassandra types to the corresponding Trino types according to the following table:

Cassandra type to Trino type mapping#
Cassandra type	Trino type	Notes
`BOOLEAN`	`BOOLEAN`
`TINYINT`	`TINYINT`
`SMALLINT`	`SMALLINT`
`INT`	`INTEGER`
`BIGINT`	`BIGINT`
`FLOAT`	`REAL`
`DOUBLE`	`DOUBLE`
`DECIMAL`	`DOUBLE`
`ASCII`	`VARCHAR`	US-ASCII character string
`TEXT`	`VARCHAR`	UTF-8 encoded string
`VARCHAR`	`VARCHAR`	UTF-8 encoded string
`VARINT`	`VARCHAR`	Arbitrary-precision integer
`BLOB`	`VARBINARY`
`DATE`	`DATE`
`TIMESTAMP`	`TIMESTAMP(3) WITH TIME ZONE`
`LIST<?>`	`VARCHAR`
`MAP<?, ?>`	`VARCHAR`
`SET<?>`	`VARCHAR`
`TUPLE`	`ROW` with anonymous fields
`UDT`	`ROW` with field names
`INET`	`IPADDRESS`
`UUID`	`UUID`
`TIMEUUID`	`UUID`

No other types are supported.

Trino type to Cassandra type mapping#

The connector maps Trino types to the corresponding Cassandra types according to the following table:

Trino type to Cassandra type mapping#
Trino type	Cassandra type	Notes
`BOOLEAN`	`BOOLEAN`
`TINYINT`	`TINYINT`
`SMALLINT`	`SMALLINT`
`INTEGER`	`INT`
`BIGINT`	`BIGINT`
`REAL`	`FLOAT`
`DOUBLE`	`DOUBLE`
`VARCHAR`	`TEXT`
`DATE`	`DATE`
`TIMESTAMP(3) WITH TIME ZONE`	`TIMESTAMP`
`IPADDRESS`	`INET`
`UUID`	`UUID`

No other types are supported.

Partition key types#

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:

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.