BGP outgoing traffic balancing between 2 uplinks

[0dm1n]

hi

I have two uplinks (2 full views). 90% of outbound traffic go thru one of them.
bgp_local_pref does not help (if I change it - another uplink get 90% of 
outbound).
The task is balance outbound ~50%/50% for two uplinks?

For example, brusquely:

filter Uplink1_in {
    if (net.len > 19 && "other_uplink_is_alive") then
       reject;
    else {
        bgp_local_pref=100;
        accept;
    }
}

I am not sure about "other_uplink_is_alive" ))
or something like routes limit 50%/50% or anything else?
Any ideas?

Thank you

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Best Wishes