[2021-10-09T03:45:22.564Z] --- FAIL: TestUpdateHistogram (0.00s)
[2021-10-09T03:45:22.564Z] panic: runtime error: index out of range [3] with length 3 [recovered]
[2021-10-09T03:45:22.564Z] panic: runtime error: index out of range [3] with length 3
[2021-10-09T03:45:22.564Z]
[2021-10-09T03:45:22.564Z] goroutine 304 [running]:
[2021-10-09T03:45:22.564Z] testing.tRunner.func1.2(0x3a04800, 0xc0085dc000)
[2021-10-09T03:45:22.564Z] /usr/local/go/src/testing/testing.go:1143 +0x332
[2021-10-09T03:45:22.565Z] testing.tRunner.func1(0xc000d5cd80)
[2021-10-09T03:45:22.565Z] /usr/local/go/src/testing/testing.go:1146 +0x4b6
[2021-10-09T03:45:22.565Z] panic(0x3a04800, 0xc0085dc000)
[2021-10-09T03:45:22.565Z] /usr/local/go/src/runtime/panic.go:965 +0x1b9
[2021-10-09T03:45:22.565Z] github.com/pingcap/tidb/statistics.mergeBuckets(0xc0139ec4e0, 0x6, 0xa, 0xc001828040, 0x6, 0x10, 0x40c3a28000000000, 0x10, 0x2745, 0x1)
[2021-10-09T03:45:22.565Z] /home/jenkins/agent/workspace/tidb_ghpr_check_2/go/src/github.com/pingcap/tidb/statistics/feedback.go:707 +0x5e9
[2021-10-09T03:45:22.565Z] github.com/pingcap/tidb/statistics.UpdateHistogram(0xc0021af3b0, 0xc002045d60, 0x2, 0xc002252000)
[2021-10-09T03:45:22.565Z] /home/jenkins/agent/workspace/tidb_ghpr_check_2/go/src/github.com/pingcap/tidb/statistics/feedback.go:770 +0x109
[2021-10-09T03:45:22.565Z] github.com/pingcap/tidb/statistics.TestUpdateHistogram(0xc000d5cd80)
[2021-10-09T03:45:22.565Z] /home/jenkins/agent/workspace/tidb_ghpr_check_2/go/src/github.com/pingcap/tidb/statistics/feedback_test.go:82 +0xe98
[2021-10-09T03:45:22.565Z] testing.tRunner(0xc000d5cd80, 0x3d166b0)
[2021-10-09T03:45:22.565Z] /usr/local/go/src/testing/testing.go:1193 +0xef
[2021-10-09T03:45:22.565Z] created by testing.(*T).Run
[2021-10-09T03:45:22.565Z] /usr/local/go/src/testing/testing.go:1238 +0x2b3

Originally posted by @tisonkun in #28549 (comment)