Hi,
spark cassandra connector / scylla fails when you attempt to make hash step with a big number of files.
I tried 1M files - always fails, 300k files - unstable, some experiments can be completed, but after a several trials it fails with error. Before each new run of hash step I used reset_db but memory is not released from scylla (I'm not ure if it's correct behaviour of DB).
Error log
```
18/04/10 23:04:51 ERROR QueryExecutor: Failed to execute: com.datastax.spark.connector.writer.RichBatchStatement@3ec8da3b
com.datastax.driver.core.exceptions.WriteTimeoutException: Cassandra timeout during write query at consistency LOCAL_QUORUM (1 replica were required but only 0 acknowled
ged the write)
at com.datastax.driver.core.exceptions.WriteTimeoutException.copy(WriteTimeoutException.java:100)
at com.datastax.driver.core.Responses$Error.asException(Responses.java:122)
at com.datastax.driver.core.RequestHandler$SpeculativeExecution.onSet(RequestHandler.java:506)
at com.datastax.driver.core.Connection$Dispatcher.channelRead0(Connection.java:1070)
at com.datastax.driver.core.Connection$Dispatcher.channelRead0(Connection.java:993)
at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:357)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:343)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:336)
at io.netty.handler.timeout.IdleStateHandler.channelRead(IdleStateHandler.java:287)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:357)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:343)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:336)
at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:357)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:343)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:336)
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:357)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:343)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:336)
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1294)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:357)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:343)
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:911)
at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:934)
at io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:397)
at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:302)
at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:131)
at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:144)
at java.lang.Thread.run(Thread.java:748)
Caused by: com.datastax.driver.core.exceptions.WriteTimeoutException: Cassandra timeout during write query at consistency LOCAL_QUORUM (1 replica were required but only
0 acknowledged the write)
at com.datastax.driver.core.Responses$Error$1.decode(Responses.java:59)
at com.datastax.driver.core.Responses$Error$1.decode(Responses.java:37)
at com.datastax.driver.core.Message$ProtocolDecoder.decode(Message.java:289)
at com.datastax.driver.core.Message$ProtocolDecoder.decode(Message.java:269)
at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:88)
... 18 more
```