Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. depoly a tidb cluster with 2 tiflash node
2. create a table t(id int);
3. let one of the tiflash down
4. alter table t set tiflash replica 1
5. select * from information_schema.TIFLASH_REPLICA; The value of AVAILABLE if always 0，and tiflash can not be used for handing query.

2. What did you expect to see? (Required)

Because there are two tiflash nodes，tiflash should be available even one of them is down.

3. What did you see instead (Required)

Tiflash replica of table t is always unavailable untile the down tiflash node is up again.

4. What is your TiDB version? (Required)

master