dns entries 1 2 3 and 4

[prem]

Hi
I have these four entires into my dns ..

primary host : say ns1.x.com
secondary : ns2.x.com
third : ns1.y.com
fourth : ns2.y.com

Now if both the dns 's are up will my site be resolved to ns1.y.com at any time ...

When will my site at y.com get seen ??? Actually I have hosted my site at x.com but suddenly today I am seeing y.com pages ...

PLS HELP

[niv]

when ns1 and ns2 .x.com are down, you'll get the others...i think. ask chicken. :D