unstable test case TestAnalyzeGlobalStatsWithOpts

[XuHuaiyu]

https://internal.pingcap.net/idc-jenkins/blue/organizations/jenkins/tidb_ghpr_unit_test/detail/tidb_ghpr_unit_test/71046/pipeline

[2021-04-14T04:16:36.078Z] FAIL: handle_test.go:821: testStatsSuite.TestAnalyzeGlobalStatsWithOpts
[2021-04-14T04:16:36.078Z] 
[2021-04-14T04:16:36.078Z] handle_test.go:848:
[2021-04-14T04:16:36.078Z]     s.checkForGlobalStatsWithOpts(c, tk, "p1", ca.topn, ca.buckets)
[2021-04-14T04:16:36.078Z] handle_test.go:812:
[2021-04-14T04:16:36.078Z]     c.Assert(len(tk.MustQuery(fmt.Sprintf("show stats_topn where partition_name='%v' and is_index=%v", p, isIdx)).Rows()), Equals, topn)
[2021-04-14T04:16:36.078Z] ... obtained int = 0
[2021-04-14T04:16:36.078Z] ... expected int = 1

[cosven]

/severity major
/sig planner

[qw4990]

I'm working on this Now, and since this issue only affects our test case, I degrade its severity to moderate.

[qw4990]

TestAnalyzeGlobalStatsWithOpts2 also has this problem.

[ti-srebot]

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[zhouqiang-cl]

happend again in https://ci.pingcap.net/blue/organizations/jenkins/tidb-unit-test-nightly/detail/tidb-unit-test-nightly/6814/pipeline