in the CDC log transformer, when creating a CDC mutation based on some
base table mutation, for each value of a base column we set the value in
the CDC column with the same name.
When looking up the column in the CDC schema by name, we may get a null
pointer if a column by that name is not found. This shouldn't happen
normally because the base schema and CDC schema should be compatible,
and for each base column there should be a CDC column with the same
name.
However, there are scenarios where the base schema and CDC schema are
incompatible for a short period of time when they are being altered.
When a base column is being added or dropped, we could get a base
mutation with this column set, and then the CDC transformer picks up the
latest CDC schema which doesn't have this column.
If such thing happens, we fix the code to throw an exception instead of
crashing on null pointer dereference. Currently we don't have a safer
approach to handle this, but this might be changed in the future. The
other alternative is dropping that data silently which we prefer not to
do.
Throwing an error is acceptable because this scenario most likely
indicates this behavior by the user:
* The user adds a new column, and start writing values to the column
before the ALTER is complete. or,
* The user drops a column, and continues writing values to the column
while it's being dropped.
Both cases might as well fail with an error because the column is not
found in the base table.
Fixesscylladb/scylladb#24952
(cherry picked from commit b336f282ae)
338ff18dfe