没有足够的副本可用于consistency LOCAL_ONE上的查询(需要1个，但只有0个活动)

Question

我正在运行spark-cassandra-connector，遇到了一个奇怪的问题:我将spark-shell运行为：

bin/spark-shell --packages datastax:spark-cassandra-connector:2.0.0-M2-s_2.1

然后我运行以下命令：

import com.datastax.spark.connector._
val rdd = sc.cassandraTable("test_spark", "test")
println(rdd.first)
# CassandraRow{id: 2, name: john, age: 29}

问题是以下命令会给出一个错误：

rdd.take(1).foreach(println)
# CassandraRow{id: 2, name: john, age: 29}
rdd.take(2).foreach(println)
# Caused by: com.datastax.driver.core.exceptions.UnavailableException: Not enough replicas available for query at consistency LOCAL_ONE (1 required but only 0 alive)
# at com.datastax.driver.core.exceptions.UnavailableException.copy(UnavailableException.java:128)
# at com.datastax.driver.core.Responses$Error.asException(Responses.java:114)
# at com.datastax.driver.core.RequestHandler$SpeculativeExecution.onSet(RequestHandler.java:467)
# at com.datastax.driver.core.Connection$Dispatcher.channelRead0(Connection.java:1012)
# at com.datastax.driver.core.Connection$Dispatcher.channelRead0(Connection.java:935)
# at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)

下面的命令挂起了：

println(rdd.count)

我的Cassandra密匙空间似乎有正确的复制因子：

describe test_spark;
CREATE KEYSPACE test_spark WITH replication = {'class': 'SimpleStrategy', 'replication_factor': '3'}  AND durable_writes = true;

如何修复上述两个错误？

Answer 1

我假设您在使用LOCAL_ONE (spark connector default)一致性时遇到了SimpleStrategy和多dc的问题。它将在本地DC中查找要向其发出请求的节点，但有可能所有副本都存在于不同的DC中，无法满足要求。(CASSANDRA-12053)

如果你change your consistency level (input.consistency.level to ONE)，我想它会被解决的。您还应该考虑改用网络拓扑策略。