unstable test TestDBStmtCount

[tiancaiamao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

cd executor
go test -v -tags intest -run  TestDBStmtCount

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

No error

3. What did you see instead (Required)

--- FAIL: TestDBStmtCount (0.67s)
    server_test.go:2160:
                Error Trace:    /home/genius/project/src/[github.com/pingcap/tidb/server/server_test.go:2160](http://github.com/pingcap/tidb/server/server_test.go:2160)
                                                        /home/genius/project/src/[github.com/pingcap/tidb/server/server_test.go:154](http://github.com/pingcap/tidb/server/server_test.go:154)
                                                        /home/genius/project/src/[github.com/pingcap/tidb/server/server_test.go:2123](http://github.com/pingcap/tidb/server/server_test.go:2123)
                                                        /home/genius/project/src/[github.com/pingcap/tidb/server/tidb_serial_test.go:1](http://github.com/pingcap/tidb/server/tidb_serial_test.go:1)
19
                Error:          Not equal:
                                expected: 3
                                actual  : 2
                Test:           TestDBStmtCount
FAIL
exit status 1

FAIL github.com/pingcap/tidb/server 0.710s

4. What is your TiDB version? (Required)

master e123433