[R] KS Test question (2)

[Ralf B]

Hi R Users,

I have two vectors, x and y, of equal length representing two types of
data from two studies. I would like to test if they are similar enough
to use them interchangeably. No assumptions about distributions can be
made (initial tests clearly show that they are not normal).
Here some result:

Two-sample Kolmogorov-Smirnov test

data:  x and y
D = 0.1091, p-value < 2.2e-16
alternative hypothesis: two-sided

Warning message:
In ks.test(x[1:nx], y[1:nx], exact = FALSE) :
  cannot compute correct p-values with ties

Here some questions:

a) What does the error message means and what does it imply?
b) The data is very noisy and the initial result shows that there is
no relation between x and y. Is there a way to calculate and effect
size?
c) Can the p-value be used, when running tests over a large amount of
different data sets, as a metric for ranking similarity between x and
y data sets?

Best
R.