unstable test TestScanOnSmallTable

[tiancaiamao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Found in CI https://do.pingcap.net/jenkins/blue/organizations/jenkins/pingcap%2Ftidb%2Fghpr_unit_test/detail/ghpr_unit_test/15023/

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

Test stable

3. What did you see instead (Required)

cd pkg/planner/core
go test -tags intest -c 
./core.test -test.run TestScanOnSmallTable 

Sometimes it pass, sometimes fails

4. What is your TiDB version? (Required)

master 6e03d23

[qw4990]

[2024/08/06 03:47:48.760 +00:00] [INFO] [analyze.go:726] ["analyze table `test`.`t` has finished"] [partition=] ["job info"="analyze table with 256 buckets, 100 topn, 1 samplerate"] ["start time"=2024/08/06 03:47:48.755 +00:00] ["end time"=2024/08/06 03:47:48.759 +00:00] [cost=4.505296ms] ["sample rate reason"="use min(1, 110000/10000) as the sample-rate=1"]
    plan_cost_ver1_test.go:135: 
        	Error Trace:	pkg/planner/core/plan_cost_ver1_test.go:135
        	Error:      	Should be true
        	Test:       	TestScanOnSmallTable
        	Messages:   	should use tikv scan, but got:
        	            	TableReader_12 10000.00 root  MppVersion: 2, data:ExchangeSender_11
        	            	└─ExchangeSender_11 10000.00 mpp[tiflash]  ExchangeType: PassThrough
        	            	  └─TableFullScan_10 10000.00 mpp[tiflash] table:t keep order:false, stats:pseudo