TiDB doesn't support primary key using pkishandle in the isolation read engines(value: 'tiflash')

[lilinghai]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

CREATE TABLE t (
  a bigint NOT NULL ,
  b int DEFAULT NULL,
  c varchar(100) NOT NULL,
  PRIMARY KEY (a) /*T![clustered_index] CLUSTERED */);
alter table t set tiflash replica 1;
set @@tidb_isolation_read_engines = 'tiflash';
select /*+ use_index(t,PRIMARY) */ count(*) from t;

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

mysql> select /*+ use_index(t,PRIMARY) */ count(*) from t;
+----------+
| count(*) |
+----------+
|        0 |
+----------+
1 row in set, 1 warning (0.07 sec)

mysql> show warnings;
+---------+------+--------------------------------------------------------------------------------------+
| Level   | Code | Message                                                                              |
+---------+------+--------------------------------------------------------------------------------------+
| Warning | 1105 | TiDB doesn't support index 'PRIMARY' in the isolation read engines(value: 'tiflash') |
+---------+------+--------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

3. What did you see instead (Required)

ERROR 1815 (HY000): Internal : No access path for table 't' is found with 'tidb_isolation_read_engines' = 'tiflash', valid values can be 'tikv'. Please check tiflash replica.

4. What is your TiDB version? (Required)

master
6b11bda