Python Cassandra 无法完成对任何主机的操作

Question

我正在尝试使用 Python 在 Apache Cassandra 上运行一些插入查询。我想从 json 文件中插入数据，这是我的代码：

import logging
from cassandra.cluster import Cluster

import json

logging.basicConfig(level=logging.INFO)


def connect_db():
    """Func to connect to cassandra db"""

    cluster = Cluster(['127.0.0.1'], port=9042)
    session = cluster.connect()

    # session.execute("DROP TABLE player_session.events")
    # session.execute("DROP TABLE player_session.startevents ")
    # session.execute("DROP TABLE player_session.endevents ")

    return session


def execute_query():
    """Func to execute query in cassandra """
    session = connect_db()

    print("Creating KEYSPACE")
    session.execute("""
        CREATE KEYSPACE IF NOT EXISTS player_session 
        WITH REPLICATION = 
        { 'class' : 'NetworkTopologyStrategy', 'data_center' : 1 }
    """)

    print("Creating player_session table")
    session.execute("""
    CREATE TABLE IF NOT EXISTS 
    player_session.events(player_id text, country text, event text, session_id text,ts timestamp, 
    PRIMARY KEY(player_id, ts)) WITH CLUSTERING ORDER BY ("ts" DESC)
    """)

    print("Creating start session table")
    session.execute("""
    CREATE TABLE IF NOT EXISTS 
    player_session.startevents(player_id text, country text, event text, session_id text,ts timestamp, 
    PRIMARY KEY(player_id, ts)) WITH CLUSTERING ORDER BY ("ts" DESC)
    """)

    print("Creating end session table")
    session.execute("""
    CREATE TABLE IF NOT EXISTS 
    player_session.endevents(player_id text, country text, event text, session_id text,ts timestamp, 
    PRIMARY KEY(player_id, ts)) WITH CLUSTERING ORDER BY ("ts" DESC)
    """)

    return session


def insert_data(session):
    """Func to insert json data """
    with open('my_json.jsonl') as f:
        data = f.readlines()

    for row in data:
        row = json.loads(row)
        if row['event'] == "start":
            session.execute(
                "INSERT INTO  player_session.startevents  (player_id,  event, country, session_id, ts) VALUES (%s,%s,%s,%s,%s) ",
                [row['player_id'], row['event'], row['country'], row['session_id'], row['ts']]
            )
        if row['event'] == "end":
            session.execute(
                "INSERT INTO  player_session.endevents  (player_id,  event, session_id, ts) VALUES (%s,%s,%s,%s) ",
                [row['player_id'], row['event'], row['session_id'], row['ts']]
            )
    f.close()
    print("data import complete")


if __name__ == "__main__":
    session = connect_db()
    insert_data(session)

我的表是在 Cassandra 中创建的，但我总是会收到此错误：

Traceback (most recent call last):
 line 64, in insert_data
    session.execute(
  File "cassandra/cluster.py", line 2618, in cassandra.cluster.Session.execute
  File "cassandra/cluster.py", line 4894, in cassandra.cluster.ResponseFuture.result
cassandra.cluster.NoHostAvailable: ('Unable to complete the operation against any hosts', {<Host: 127.0.0.1:9042 datacenter1>: Unavailable('Error from server: code=1000 [Unavailable exception] message="Cannot achieve consistency level LOCAL_ONE" info={\'consistency\': \'LOCAL_ONE\', \'required_replicas\': 1, \'alive_replicas\': 0}')})

Answer 1

错误信息提示了两种可能性：

1. Cassandra 没有运行。您可以通过nodetool status 验证这一点。

2. 您用于连接的数据中心名称在键空间定义或集群配置中不正确。数据中心的默认名称是dc1。无论设置为什么，它都必须与nodetool status、describe keyspace player_session 中显示的数据中心名称以及连接属性中指定的数据中心名称相匹配（可选）。