Revert "executor: fix show global variables return session variables also (#19341) (#21045)"

[bb7133]

This reverts commit a1bdbef.

What problem does this PR solve?

Issue Number: close #24326 for TiDB v4.0

Problem Summary:

• Manual test (add detailed scripts or steps below)

The following code is used to do the tests:

class Test1 {    
   public static void main(String[] args) throws Exception {    
        System.setProperty( "oracle.jdbc.Trace", Boolean.TRUE.toString() );    
        Class.forName("com.mysql.jdbc.Driver").newInstance();    
        String url = "jdbc:mysql://address=(protocol=tcp)(host=127.0.0.1)(port=4000)(user=root)/test?&useUnicode=true&characterEncoding=UTF-8";    
        Connection conn = DriverManager.getConnection(url, "", "");    
        DatabaseMetaData meta = conn.getMetaData();    
        System.out.println("Driver version: " + meta.getDriverVersion());    
        System.out.println("Server version: " + meta.getDatabaseProductVersion());    
    
        int connId = 0;    
        while (connId < 20) {    
            try {    
                long startTime = System.currentTimeMillis();    
                conn = DriverManager.getConnection(url, "", "");    
                long duration = System.currentTimeMillis() - startTime;    
                System.out.println("Time for onConnection #" + connId + ": " + duration);    
                connId ++;    
            } catch (Exception e) {    
                System.out.println("Exception: "+e);    
                e.printStackTrace();    
            } finally {    
                conn.close();    
            }    
        }    
    }    
}   

Before this PR, a long connection duration can be noticed because of #24326 and the MySQL connector bug #75592:

Driver version: mysql-connector-java-5.1.34 ( Revision: [email protected] )
Server version: 5.7.25-TiDB-v4.0.14
Time for onConnection #0: 71
Time for onConnection #1: 53
Time for onConnection #2: 48
Time for onConnection #3: 45
Time for onConnection #4: 74
Time for onConnection #5: 63
Time for onConnection #6: 44
Time for onConnection #7: 42
Time for onConnection #8: 37
Time for onConnection #9: 40
Time for onConnection #10: 50
Time for onConnection #11: 68
Time for onConnection #12: 40
Time for onConnection #13: 56
Time for onConnection #14: 41
Time for onConnection #15: 43
Time for onConnection #16: 41
Time for onConnection #17: 48
Time for onConnection #18: 96
Time for onConnection #19: 54

After reverting the commit, the duration of connection reduced:

Driver version: mysql-connector-java-5.1.34 ( Revision: [email protected] )
Server version: 5.7.25-TiDB-v4.0.14-1-geea91a40c
Time for onConnection #0: 12
Time for onConnection #1: 18
Time for onConnection #2: 16
Time for onConnection #3: 16
Time for onConnection #4: 24
Time for onConnection #5: 27
Time for onConnection #6: 25
Time for onConnection #7: 17
Time for onConnection #8: 19
Time for onConnection #9: 17
Time for onConnection #10: 16
Time for onConnection #11: 15
Time for onConnection #12: 17
Time for onConnection #13: 21
Time for onConnection #14: 14
Time for onConnection #15: 15
Time for onConnection #16: 14
Time for onConnection #17: 16
Time for onConnection #18: 18
Time for onConnection #19: 15

Side effects

• This PR brings show global variables statement returns session variables also #18517 back.

Documentation

• To be added

Release note

• Revert executor: fix show global variables return session variables also (#19341) #21045 to avoid show session variables is very slow on first run #24326.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• guo-shaoge
• zimulala

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[qw4990]

/run-all-tests

[qw4990]

/run-integration-test

[guo-shaoge]

/run-integration-common-test
/run-common-test

[bb7133]

/run-integration-common-test
/run-common-test

[zimulala]

After reverting the commit, duration of connection reduced.

Could you briefly describe the reduction in execution time? The approximate time is reduced from how many milliseconds to how many milliseconds？

[zhouqiang-cl]

/hold

[ti-chi-bot]

@bb7133: Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[zhouqiang-cl]

/unhold

[zimulala]

LGTM

You need two LGTMS

[bb7133]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 38c283b