Today’s trivial MySQL system variable:
old_alter_table
The interesting bit is that this is a system variable, and shows up in SHOW GLOBAL VARIABLES, but is not documented on the Server System Variables manual page.
Instead, it is documented on the manual page for Server options.
Unfortunately, that documentation is very sparse. It tells us:
old-alter-table is an option that can be set in an
option file (such as /etc/my.cnf)
old_alter_table is the name of the variable.
And….that’s it. It is neither a system nor status variable, there is no scope, and no entry for whether or not it is dynamic. These last 2 are baffling, though they show up in other variables in the …
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