routing问题（生产环境发现一个分片上的数据为空）

生产环境发现一个分片上的数据为空，为了测试依次执行如下：
 /routing_test/data/0?routing=0
{
  "name": "0"
}
 
/routing_test/data/1?routing=1
{
  "name": "1"
}
 
/routing_test/data/2?routing=2
{
  "name": "2"
}
 
/routing_test/data/3?routing=3
{
  "name": "3"
}
 
/routing_test/data/4?routing=4
{
  "name": "4"
}
 
最后执行 _cat/shards/routing_test?v&h=index,shard,prirep,state,docs,store

index        shard prirep state   docs store 

routing_test 2     p      STARTED    2 5.9kb 

routing_test 1     p      STARTED    0  130b 

routing_test 4     p      STARTED    1   3kb 

routing_test 3     p      STARTED    1   3kb 

routing_test 0     p      STARTED    1   3kb

为什么分片1上没有数据，而分片2上两条数据呢？