即使在覆盖超时之后，Cassandra ReadTimeoutException 也会在表中获取所有记录

Question

所以，我正在尝试使用 Java datastax 3.1 驱动程序和以下查询级别设置来获取 cassandra 表中的所有记录（约 10K 记录）：

// |query| reads all records in a table (select * from table)
// Setting read timeout as 10 minutes
query.setReadTimeoutMillis(600000);
// Set page size as 1000
query.setFetchSize(1000);

Cassandra 服务器设置为默认设置（所有默认超时）。它是一个 3 节点集群。

驱动程序能够成功读取前 1000 条记录，但每次驱动程序尝试获取接下来的 1000 条记录时，我都会收到以下错误。

com.datastax.driver.core.exceptions.ReadTimeoutException: Cassandra timeout during read query at consistency LOCAL_ONE (1 responses were required but only 0 replica responded)
    at com.datastax.driver.core.exceptions.ReadTimeoutException.copy(ReadTimeoutException.java:88)
    at com.datastax.driver.core.exceptions.ReadTimeoutException.copy(ReadTimeoutException.java:25)
    at com.datastax.driver.core.DriverThrowables.propagateCause(DriverThrowables.java:37)
    at com.datastax.driver.core.ArrayBackedResultSet$MultiPage.prepareNextRow(ArrayBackedResultSet.java:312)
    at com.datastax.driver.core.ArrayBackedResultSet$MultiPage.isExhausted(ArrayBackedResultSet.java:269)
    at com.datastax.driver.core.ArrayBackedResultSet$1.hasNext(ArrayBackedResultSet.java:143)
    ... <some more stacktrace of custom codebase trying to read all rows in a table>
Caused by: com.datastax.driver.core.exceptions.ReadTimeoutException: Cassandra timeout during read query at consistency LOCAL_ONE (1 responses were required but only 0 replica responded)
    at com.datastax.driver.core.exceptions.ReadTimeoutException.copy(ReadTimeoutException.java:115)
    at com.datastax.driver.core.Responses$Error.asException(Responses.java:124)
    at com.datastax.driver.core.RequestHandler$SpeculativeExecution.onSet(RequestHandler.java:500)
    at com.datastax.driver.core.Connection$Dispatcher.channelRead0(Connection.java:1012)
    at com.datastax.driver.core.Connection$Dispatcher.channelRead0(Connection.java:935)
    at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:342)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:328)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:321)
    at io.netty.handler.timeout.IdleStateHandler.channelRead(IdleStateHandler.java:266)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:342)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:328)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:321)
    at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:342)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:328)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:321)
    at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:293)
    at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:267)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:342)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:328)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:321)
    at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1280)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:342)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:328)
    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:890)
    at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:131)
    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:564)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:505)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:419)
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:391)
    at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:112)
    at java.lang.Thread.run(Thread.java:748)
Caused by: com.datastax.driver.core.exceptions.ReadTimeoutException: Cassandra timeout during read query at consistency LOCAL_ONE (1 responses were required but only 0 replica responded)
    at com.datastax.driver.core.Responses$Error$1.decode(Responses.java:62)
    at com.datastax.driver.core.Responses$Error$1.decode(Responses.java:37)
    at com.datastax.driver.core.Message$ProtocolDecoder.decode(Message.java:277)
    at com.datastax.driver.core.Message$ProtocolDecoder.decode(Message.java:257)
    at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:88)
    ... 19 common frames omitted 

因此，读取表中所有记录的服务进入了崩溃循环，每次都出现相同的异常。

令我惊讶的是，在读取第 1000 条记录后恰好 10 秒后，此异常始终发生。默认情况下，10 秒似乎是 cassandra 服务器端超时，对于我的查询，它应该被覆盖为 600 秒（显然这没有发生）。谁能向我解释为什么会发生这种情况？

附： - 苦苦寻找根本原因后，我重新启动了cassandra。瞧！，之后一切都很顺利，所有记录都被分页读取并处理，没有任何麻烦。

Answer 1

select * from table 是不好的模式 - Cassandra 没有针对它进行优化，因此它需要从所有节点获取数据，并通过协调节点进行流式传输。在 Cassandra 中访问数据最有效的方法是通过指定分区键（可能在集群列上附加条件）。

如果确实需要扫描集群中的所有数据，则需要实现为一组token range查询，遍历集群中的所有range（可以通过Java或Python驱动的Metadataclass获取token range )。