Hi, Nikita,

This is good, but I think fill_extra_persistent_columns() shouldn't be
used at all.

It doesn't handle default values. I've changed rpl_alter_extra_persistent test
as

-alter table t1 add column z1 int as(a+1) virtual, add column z2 int as (a+2) persistent;
+alter table t1 add column z1 int as(a+1) virtual, add column z2 int default (a+2);

and, of course, new column z2 wasn't updated properly.
An easy fix would be to use your code in all cases and remove
fill_extra_persistent_columns().

Could you do that too, please? And add the test case too. May be just,
append

   , add column z3 int default (a+2)