Cassandra Demo--Python操作cassandra

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创建keyspace和table

CREATE KEYSPACE exps  
WITH REPLICATION = { 'class' : 'NetworkTopologyStrategy', 'DC1' : 2 };

create table exps_user(user_id int primary key,user_name varchar,user_info text);

create index idx_user_name on exps_user(user_name);

 注意在创建keyspace时，数据中心的名称需要区分大小写，如果数据中心名称写错，创建keyspace和table能成功，但INSERT数据时会报错。

在cqlsh上报NoHostAvailable错误，如果使用python访问，会报下面错误：

Error from server: code=1000 [Unavailable exception] message="Cannot achieve consistency level LOCAL_ONE" info={'consistency': 'LOCAL_ONE', 'required_replicas': 1, 'alive_replicas': 0}

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需要安装python依赖包cassandra-driver：

from cassandra.cluster import Cluster
from cassandra.policies import DCAwareRoundRobinPolicy
from cassandra import ConsistencyLevel

cluster_instances = ['192.168.199.171', '192.168.199.172', '192.168.199.173']
cluster = Cluster(
    cluster_instances,
    load_balancing_policy=DCAwareRoundRobinPolicy(local_dc='DC1'),
    port=9042
)

session = cluster.connect("exps")
for user_id in range(1, 50000):
    try:
        sql_script = ("insert into exps_user(user_id,user_name,user_info)"
                      "VALUES({0},'U{0}','THIS IS TEST');").format(user_id)
        user_lookup_stmt = session.prepare(sql_script)
        user_lookup_stmt.consistency_level = ConsistencyLevel.LOCAL_ONE
        user1 = session.execute(user_lookup_stmt, [])
    except Exception as ex:
        print(str(ex))