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Scylla Specific Features

Shard Awareness

scylla-driver is shard aware and contains extensions that work with the TokenAwarePolicy supported by Scylla 2.3 and onwards. Using this policy, the driver can select a connection to a particular shard based on the shard's token. As a result, latency is significantly reduced because there is no need to pass data between the shards.

Details on the scylla cql protocol extensions https://github.com/scylladb/scylla/blob/master/docs/design-notes/protocol-extensions.md

For using it you only need to enable TokenAwarePolicy on the Cluster

from cassandra.cluster import Cluster
from cassandra.policies import TokenAwarePolicy, RoundRobinPolicy

cluster = Cluster(load_balancing_policy=TokenAwarePolicy(RoundRobinPolicy()))

New Cluster Helpers

  • cluster.is_shard_aware()

    New method available on Cluster allowing to check whether the remote cluster supports shard awareness (bool)

from cassandra.cluster import Cluster

cluster = Cluster()
session = cluster.connect()

if cluster.is_shard_aware():
    print("connected to a scylla cluster")

  • cluster.shard_aware_stats()

    New method available on Cluster allowing to check the status of shard aware connections to all available hosts (dict)

from cassandra.cluster import Cluster

cluster = Cluster()
session = cluster.connect()

stats = cluster.shard_aware_stats()
if all([v["shards_count"] == v["connected"] for v in stats.values()]):
    print("successfully connected to all shards of all scylla nodes")

New Table Attributes

  • in_memory flag

    New flag available on TableMetadata.options to indicate that it is an In Memory table

Note

in memory tables is a feature existing only in Scylla Enterprise

from cassandra.cluster import Cluster

cluster = Cluster()
session = cluster.connect()
session.execute("""
    CREATE KEYSPACE IF NOT EXISTS keyspace1
    WITH replication = {'class': 'SimpleStrategy', 'replication_factor': '1'};
""")

session.execute("""
    CREATE TABLE IF NOT EXISTS keyspace1.standard1 (
        key blob PRIMARY KEY,
        "C0" blob
    ) WITH in_memory=true AND compaction={'class': 'InMemoryCompactionStrategy'}
""")

cluster.refresh_table_metadata("keyspace1", "standard1")
assert cluster.metadata.keyspaces["keyspace1"].tables["standard1"].options["in_memory"] == True