I've read in some posts that having duplicate partitioning key can have a performance impact. I've two tables like:

CREATE TABLE "Test1" (               CREATE TABLE "Test2" (
  key text,                          key text,
  column1 text,                      name text,
  value text,                        age text,             
  PRIMARY KEY (key, column1)         ...
)                                    PRIMARY KEY (key, name,age)
                                     )

In Test1 column1 will contain column name and value will contain its corresponding value.The main advantage of Test1 is that I can add any number of column/value pairs to it without altering the table by just providing same partitioning key each time.

Now my question is how will each of these table schema's impact the read/write performance if I've millions of rows and number of columns can be upto 50 in each row. How will it impact the compaction/repair time if I'm writing duplicate entries frequently?