issue with irule

If HTTP Keep-Alive is in use in the client-side (and it probably is) then the client may make multiple requests over a single TCP connection. In that case, HTTP_REQUEST will fire for each client HTTP request. If you want it to happen only once per TCP connection:

when CLIENT_ACCEPTED {
    set hit_test 0    
}

when HTTP_REQUEST {
    if { [HTTP::path starts_with "/xyz" and !$hit_test } {    
        log local0. "..."        
        set hit_test 1        
    }    
}

You should also consider remote logging using High Speed Logging, rather than local logging.