Version 3.0 of the DataStax Python driver for Apache Cassandra adds support for Cassandra 3.0 while maintaining support for previously supported versions. In addition to substantial internal rework, there are several updates to the API that integrators will need to consider:
Default consistency is nowLOCAL_ONE¶
Previous value was ONE. The new value is introduced to mesh with the default DC-aware load balancing policy and to match other drivers.
Previously results would be returned as a list of rows for result rows up to fetch_size, and PagedResult afterward. This could break application code that assumed one type and got another.
Now, all results are returned as an iterable ResultSet.
The preferred way to consume results of unknown size is to iterate through them, letting automatic paging occur as they are consumed.
results = session.execute("SELECT * FROM system.local")
for row in results:
process(row)
If the expected size of the results is known, it is still possible to materialize a list using the iterator:
results = session.execute("SELECT * FROM system.local")
row_list = list(results)
For backward compatability, ResultSet supports indexing. When accessed at an index, a ~.ResultSet object will materialize all its pages:
results = session.execute("SELECT * FROM system.local")
first_result = results[0] # materializes results, fetching all pages
This can send requests and load (possibly large) results into memory, so ~.ResultSet will log a warning on implicit materialization.
blist removed as soft dependency¶Previously the driver had a soft dependency on blist sortedset, using that where available and using an internal fallback where possible.
Now, the driver never chooses the blist variant, instead returning the internal util.SortedSet for all set results. The class implements all standard set operations, so no integration code should need to change unless it explicitly checks for sortedset type.
ResponseFuture.result timeout parameter is removed, use Session.execute timeout instead (031ebb0)Cluster.refresh_schema removed, use Cluster.refresh_*_metadata instead (419fcdf)Cluster.submit_schema_refresh removed (574266d)cqltypes time/date functions removed, use util entry points instead (bb984ee)decoder module removed (e16a073)TableMetadata.keyspace attribute replaced with keyspace_name (cc94073)cqlengine.columns.TimeUUID.from_datetime removed, use util variant instead (96489cc)cqlengine.columns.Float(double_precision) parameter removed, use columns.Double instead (a2d3a98)cqlengine keyspace management functions are removed in favor of the strategy-specific entry points (4bd5909)cqlengine.Model.__polymorphic_*__ attributes removed, use __discriminator* attributes instead (9d98c8e)cqlengine.statements will no longer warn about list list prepend behavior (79efe97)Version 2.1 of the DataStax Python driver for Apache Cassandra adds support for Cassandra 2.1 and version 3 of the native protocol.
Cassandra 1.2, 2.0, and 2.1 are all supported. However, 1.2 only supports protocol version 1, and 2.0 only supports versions 1 and 2, so some features may not be available.
Using the v3 Native Protocol¶By default, the driver will attempt to use version 2 of the native protocol. To use version 3, you must explicitly set the protocol_version:
from cassandra.cluster import Cluster cluster = Cluster(protocol_version=3)
Note that protocol version 3 is only supported by Cassandra 2.1+.
In future releases, the driver may default to using protocol version 3.
Working with User-Defined Types¶Cassandra 2.1 introduced the ability to define new types:
USE KEYSPACE mykeyspace; CREATE TYPE address (street text, city text, zip int);
The driver generally expects you to use instances of a specific class to represent column values of this type. You can let the driver know what class to use with Cluster.register_user_type():
cluster = Cluster()
class Address(object):
def __init__(self, street, city, zipcode):
self.street = street
self.city = text
self.zipcode = zipcode
cluster.register_user_type('mykeyspace', 'address', Address)
When inserting data for address columns, you should pass in instances of Address. When querying data, address column values will be instances of Address.
If no class is registered for a user-defined type, query results will use a namedtuple class and data may only be inserted though prepared statements.
See User Defined Types for more details.
Customizing Encoders for Non-prepared Statements¶Starting with version 2.1 of the driver, it is possible to customize how Python types are converted to CQL literals when working with non-prepared statements. This is done on a per-Session basis through Session.encoder:
cluster = Cluster() session = cluster.connect() session.encoder.mapping[tuple] = session.encoder.cql_encode_tuple
See Type Conversions for the table of default CQL literal conversions.
Using Client-Side Protocol-Level Timestamps¶With version 3 of the native protocol, timestamps may be supplied by the client at the protocol level. (Normally, if they are not specified within the CQL query itself, a timestamp is generated server-side.)
When protocol_version is set to 3 or higher, the driver will automatically use client-side timestamps with microsecond precision unless Session.use_client_timestamp is changed to False. If a timestamp is specified within the CQL query, it will override the timestamp generated by the driver.
Version 2.0 of the DataStax Python driver for Apache Cassandra includes some notable improvements over version 1.x. This version of the driver supports Cassandra 1.2, 2.0, and 2.1. However, not all features may be used with Cassandra 1.2, and some new features in 2.1 are not yet supported.
Using the v2 Native Protocol¶By default, the driver will attempt to use version 2 of Cassandra’s native protocol. You can explicitly set the protocol version to 2, though:
from cassandra.cluster import Cluster cluster = Cluster(protocol_version=2)
When working with Cassandra 1.2, you will need to explicitly set the protocol_version to 1:
from cassandra.cluster import Cluster cluster = Cluster(protocol_version=1)Automatic Query Paging¶
Version 2 of the native protocol adds support for automatic query paging, which can make dealing with large result sets much simpler.
See Paging Large Queries for full details.
Protocol-Level Batch Statements¶With version 1 of the native protocol, batching of statements required using a BATCH cql query. With version 2 of the native protocol, you can now batch statements at the protocol level. This allows you to use many different prepared statements within a single batch.
See BatchStatement for details and usage examples.
Also new in version 2 of the native protocol is SASL-based authentication. See the section on Security for details and examples.
Calling Cluster.shutdown()¶In order to fix some issues around garbage collection and unclean interpreter shutdowns, version 2.0 of the driver requires you to call Cluster.shutdown() on your Cluster objects when you are through with them. This helps to guarantee a clean shutdown.
The following dependencies have officially been made optional:
scalesblistAnd one new dependency has been added (to enable Python 3 support):
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