optimistic locks block read

[seiya-annie]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. create table t(pk int primary key, v int, uk int, nuk int, key uk1(uk), key nuk1(nuk)) partition by list(pk) (PARTITION p0 VALUES in (1,2), PARTITION p1 VALUES in (3,4), PARTITION p2 VALUES in (5,6), PARTITION p3 VALUES in (7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100))

2. // Read meets optimistic locks. Skip them and read old data
   drop table if exists t
   insert into t values (1, 1, 1, 1), (2, 2, 2, 2), (3, 3, 3, 3)
   try(cli.EnableFailpoint(resource.TiDB, beforeCommitFp, "pause"))
   begin pessimistic
   update t set v = v + 1
   commit

   begin
   select t1.v from (%s) as t1 order by t1.v

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

read successful

3. What did you see instead (Required)

read fail with "optimistic locks shouldn't block read"

4. What is your TiDB version? (Required)

master

[cfzjywxk]

@crazycs520
PTAL if you have time, it relates to a test case failure reporeted by @seiya-annie