Cassandra 3.10 has partial partition key search but does it result in a table scan?

[Kant Kodali]

Hi All,

It looks like Cassandra 3.10 has partial partition key search but does it
result in a table scan? for example I can have the following

create table hello(
a text,
b int,
c text,
d text,
primary key((a,b), c)
);

Now I can do select * from hello where a='foo' allow filtering;// This
works in 3.10 but I wonder if this query results in table scan and if so is
there any way to limit such that I get max b?

Thanks!