Replying to client’s queries SELECT @@AUTOCOMMIT without need of backend

[yashwantsahu20]

Replying to client’s queries SELECT @@autocommit without need of backend
The query should also not disabling multiplexing.

For details Please see:
https://github.com/ProxySQL/proxysql_3p_testing/issues/13

[renecannao]

Can one of the admins verify this patch?

[yashwantsahu20]

Please ignore first commit message. As incorrectly I have mention SELECT @@Version instead of SELECT @@autocommit

[renecannao]

add to whitelist

[renecannao]

Initial requirement:

Reply to client’s queries SELECT @@AUTOCOMMIT (and also lowercase) returning the value of autocommit defined at MySQL session level, without the need of any backend. For reference, we already have a similar implementation for SELECT LAST_INSERT_ID() . The query should also not disable multiplexing. The implementation also requires adequate TAP test to verify the functionality .

[renecannao]

We can avoid hardcoding the number of queries, but consider the size of states[]

Same thing applies for plan() : it can be computed based on the content of states[] .

The above consideration is related to the fact that:

1. autocommit is changed from 1 (implicit) to 0 and then to 1 (explicitly), but never changed back to 0 (and eventually back to 1) to test multiple changes
2. queries all have SELECT uppercase and autocommit lowercase : no combination of uppercase and lowercase are tested
3. values 0 and 1 are used , while ON/OFF/true/FaLsE/etc are not tested

The test doesn't verify that no backend was used, neither that multiplexing was not disabled.

[JavierJF]

I was going to propose to reuse other test for this purpose. All the feedback from the previous comment can be taken into modifying a test like reg_test_3549-autocommit_tracking-t.cpp which performs more complex queries, and already tracks autocommit, so should be a matter of doing an (extra) consistency check between the present tracking and SELECT @@autocommit. For addressing the part of the feedback about multiplexing disabling, the utility function check_multiplexing_disabled from test_keep_multiplexing_variables-t.cpp can also be moved to utils.cpp and reused.

[renecannao]

I am curious: why this?

If used to add come entropy, we could run after every SET/SELECT

[JavierJF]

Based on a response from MySQL 5.7.44-log:

    Packet Length: 34
    Packet Number: 2
    Catalog
        Catalog: def
    Database
        Database:
    Table
        Table:
    Original table
        Original table:
    Name
        Name: @@autocommit
    Original name
        Original name:
    Charset number: binary COLLATE binary (63)
    Length: 1
    Type: FIELD_TYPE_LONGLONG (8)
    Flags: 0x0080
        .... .... .... ...0 = Not null: Not set
        .... .... .... ..0. = Primary key: Not set
        .... .... .... .0.. = Unique key: Not set
        .... .... .... 0... = Multiple key: Not set
        .... .... ...0 .... = Blob: Not set
        .... .... ..0. .... = Unsigned: Not set
        .... .... .0.. .... = Zero fill: Not set
        .... ...0 .... .... = Enum: Not set
        .... ..0. .... .... = Auto increment: Not set
        .... .0.. .... .... = Timestamp: Not set
        .... 0... .... .... = Set: Not set
    Decimals: 0
MySQL Protocol - row packet
    Packet Length: 2
    Packet Number: 3
    text
        text: 1

• Size for the field of 1 instead of 31. Most probably this won't be an issue, yet this could be confusing from client side.
• Flags should be 0x80 (binary_flag), instead of (0xa1).

[JavierJF]

I was going to propose to reuse other test for this purpose. All the feedback from the previous comment can be taken into modifying a test like reg_test_3549-autocommit_tracking-t.cpp which performs more complex queries, and already tracks autocommit, so should be a matter of doing an (extra) consistency check between the present tracking and SELECT @@autocommit. For addressing the part of the feedback about multiplexing disabling, the utility function check_multiplexing_disabled from test_keep_multiplexing_variables-t.cpp can also be moved to utils.cpp and reused.