The new test case:

To reproduce the issue we can use the 101_initial_cluster.sh example. Once our sample cluster is running, if we select for instance the @@autocommit variable, the result will be as followed:

mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|         NULL |
+--------------+
1 row in set (0.01 sec)

A fix has been introduced in 34ffa84 allowing the EvalEngine to handle 32-bit variables. It seems that 64-bit variables are used by queries that needs to communicate with MySQL, and 32-bit are used for VTGate-only query.

Unit tests have been modified accordingly.

The behavior now is as followed:

examples/local $  ./101_initial_cluster.sh

...

examples/local $  mysql

...

mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|            1 |
+--------------+
1 row in set (0.00 sec)

Ran on:

Version: da7611d87 (Git branch 'fix-7301') built on Sat Jan 23 18:05:31 CET 2021 by pflorent@florents-macbook-pro.home using go1.15.7 darwin/amd64

Up until now, boolean bind variables were typed int32 within vtgate. Though, MySQL uses 64-bit, meaning that we were facing a type inconsistency problem.

For instance, the following query returns a type int32:

select @@autocommit

Whereas the following query returns a type int64:

select @@autocommit from my_table

To suppress this problem, @systay and I decided upon using int64 variables for boolean bind variables. Changes were performed in both 0294465 and 2d91120.