unstable test case: TestTraceCE

[time-and-fate]

Bug Report

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1. Minimal reproduce step (Required)

https://ci.pingcap.net/blue/rest/organizations/jenkins/pipelines/tidb_ghpr_check_2/runs/48874/nodes/62/steps/73/log/?start=0

[2021-11-29T10:18:05.918Z]         	            	Diff:
[2021-11-29T10:18:05.918Z]         	            	--- Expected
[2021-11-29T10:18:05.918Z]         	            	+++ Actual
[2021-11-29T10:18:05.918Z]         	            	@@ -5,3 +5,3 @@
[2021-11-29T10:18:05.918Z]         	            	   Type: (string) (len=26) "Table Stats-Expression-CNF",
[2021-11-29T10:18:05.918Z]         	            	-  Expr: (string) (len=17) "`lt`(test.t.b, 4)",
[2021-11-29T10:18:05.918Z]         	            	+  Expr: (string) (len=17) "`lt`(test.t.a, 3)",
[2021-11-29T10:18:05.918Z]         	            	   RowCount: (uint64) 6
[2021-11-29T10:18:05.918Z]         	            	@@ -12,3 +12,3 @@
[2021-11-29T10:18:05.918Z]         	            	   Type: (string) (len=26) "Table Stats-Expression-CNF",
[2021-11-29T10:18:05.918Z]         	            	-  Expr: (string) (len=17) "`lt`(test.t.b, 4)",
[2021-11-29T10:18:05.918Z]         	            	+  Expr: (string) (len=17) "`lt`(test.t.a, 3)",
[2021-11-29T10:18:05.918Z]         	            	   RowCount: (uint64) 6
[2021-11-29T10:18:05.918Z]         	            	@@ -26,3 +26,3 @@
[2021-11-29T10:18:05.918Z]         	            	   Type: (string) (len=26) "Table Stats-Expression-CNF",
[2021-11-29T10:18:05.918Z]         	            	-  Expr: (string) (len=17) "`lt`(test.t.a, 3)",
[2021-11-29T10:18:05.918Z]         	            	+  Expr: (string) (len=17) "`lt`(test.t.b, 4)",
[2021-11-29T10:18:05.918Z]         	            	   RowCount: (uint64) 6
[2021-11-29T10:18:05.918Z]         	            	@@ -33,3 +33,3 @@
[2021-11-29T10:18:05.918Z]         	            	   Type: (string) (len=26) "Table Stats-Expression-CNF",
[2021-11-29T10:18:05.918Z]         	            	-  Expr: (string) (len=17) "`lt`(test.t.a, 3)",
[2021-11-29T10:18:05.918Z]         	            	+  Expr: (string) (len=17) "`lt`(test.t.b, 4)",
[2021-11-29T10:18:05.918Z]         	            	   RowCount: (uint64) 6
[2021-11-29T10:18:05.918Z]         	Test:       	TestTraceCE

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

The test case TestTraceCE runs successfully.

3. What did you see instead (Required)

Sometimes it may fail because we assert two slices to be equal. But we actually don't care about the order of the elements.

4. What is your TiDB version? (Required)

master

[time-and-fate]

/assign

[github-actions]

Please check whether the issue should be labeled with 'affects-x.y' or 'fixes-x.y.z', and then remove 'needs-more-info' label.