Integration Push Down Test unstable

[danmay319]

Bug Report

Integration Push Down Test is not stable.

1. What did you do?

/run-integration-copr-test in #16830

2. What did you expect to see?

Succeed

3. What did you see instead?

Fail

[2020-04-30T05:36:14.101Z] 2020/04/30 13:36:13 2020/04/30 13:35:51 Test fail: Outputs are not matching.
[2020-04-30T05:36:14.101Z] Test case: sql/randgen-limit/7_str_1.sql
[2020-04-30T05:36:14.101Z] Statement: #514 - SELECT UNHEX( ( CONCAT( col_float ) ) ) AS field1 FROM table1_int_autoinc WHERE CONCAT( ( '18:02:07.032977' / '1998-04-26' ), ( ~ col_int ) ) LIMIT 11 /* QNO 516 CON_ID 212 */ ;
[2020-04-30T05:36:14.101Z] NoPushDown Output:
[2020-04-30T05:36:14.101Z] field1
[2020-04-30T05:36:14.102Z]
[2020-04-30T05:36:14.102Z]
[2020-04-30T05:36:14.102Z] WithPushDown Output:
[2020-04-30T05:36:14.102Z] field1
[2020-04-30T05:36:14.102Z] $E

4. What version of TiDB are you using? (tidb-server -V or run select tidb_version(); on TiDB)

Release Version: v4.0.0-beta.2-369-g0e5af57f6-dirty
Git Commit Hash: 0e5af57
Git Branch: issue16910
UTC Build Time: 2020-04-28 08:36:13
GoVersion: go1.13
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false

[SunRunAway]

Is it a duplicate to #16629?