Evaluate system variables #6708
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Signed-off-by: Andres Taylor <andres@planetscale.com>
Signed-off-by: Andres Taylor <andres@planetscale.com>
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Signed-off-by: Andres Taylor <andres@planetscale.com>
Signed-off-by: Andres Taylor <andres@planetscale.com>
Signed-off-by: Andres Taylor <andres@planetscale.com>
Signed-off-by: Andres Taylor <andres@planetscale.com>
…variables Only settings which are kept in the session state, and which cannot be changed using vtgate startup flags are supported. Signed-off-by: Andres Taylor <andres@planetscale.com>
Signed-off-by: Andres Taylor <andres@planetscale.com>
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Signed-off-by: Andres Taylor <andres@planetscale.com>
harshit-gangal
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Sep 17, 2020
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Some system variables influence Vitess' behaviour, and are kept in the session state and never sent down to the backing MySQL instances.
Earlier, if a query included the evaluation of such a system variable, for example in an simple query like:
select @@transaction_modeVitess didn't handle these expressions, and they were simply sent down to the backing MySQL instance. This PR rectifies this situation and rewrites away these expressions and injects the session value instead of relying of the underlying MySQL reflecting the same state.