store/tikv,session: invalidate snapshot cache under pessimistic transaction

[tiancaiamao]

What problem does this PR solve?

Fix a bug in the pessimistic transaction that the transaction snapshot doesn't invalidate its cache after the snapshotTS changes.

insert into conflict values (1, 2);
begin pessimistic;
insert ignore into conflict values (1, 2);

update conflict set c = c - 1     // in another terminal

select * from conflict where id = 1 for update
insert into conflict values (1, 999) on duplicate key update c = c + 2
commit

select * from conflict

Expect:

mysql> select * from conflict;
+----+------+
| id | c    |
+----+------+
|  1 |    3 |
+----+------+
1 row in set (0.00 sec)

Get:

mysql> select * from conflict;
+----+------+
| id | c    |
+----+------+
|  1 |    4 |
+----+------+
1 row in set (0.00 sec)

What is changed and how it works?

In a pessimistic transaction, the snapshotTS may change, so we should invalidate
the cache if the snapshotTS changes

Check List

Tests

• Unit test

[tiancaiamao]

PTAL @coocood @jackysp

[codecov]

Codecov Report

Merging #12147 into master will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master     #12147   +/-   ##
===========================================
  Coverage   81.3581%   81.3581%           
===========================================
  Files           453        453           
  Lines         97356      97356           
===========================================
  Hits          79207      79207           
  Misses        12485      12485           
  Partials       5664       5664

[tiancaiamao]

I've updated the test case @coocood

[coocood]

LGTM

[jackysp]

LGTM

[sre-bot]

/run-all-tests