Hi, all
  I write a program to test the cassandra2.1. I have 6 nodes cluster.
  First, I insert 1 million row data into cassandra. the row key from 1 to 1000000.

  Then I run my test program. My test program first delete(use batch mutate) the row and insert (use batch mutate) that row,

     then read (use gen_slice_range) the same row. After that check whether the read data is same with the insert data or not.

  The consistency level used is quorum.

  I found there some cases that not the same. About 1/10000. In this error cases, some column is not same.

  Then I use cassandra-cli to check the data, found that column is not exist. It seems insert partly.

  My test program has 20 threads. the QPS 800 about

  What's wrong with cassandra??