Re: Support load balancing in libpq

> we can assume that one of members is a primary and others are secondary.

With plain Postgres this assumption is probably correct. But the main reason
I'm interested in this patch was because I would like to be able to load
balance across the workers in a Citus cluster. These workers are all primaries.
Similar usage would likely be possible with BDR (bidirectional replication).

> In this case user maybe add a primary host to top of the list,
> so sorting may increase time durations for establishing connection.

If the user takes such care when building their host list, they could simply
not add the load_balance_hosts=true option to the connection string.
If you know there's only one primary in the list and you're looking for
the primary, then there's no reason to use load_balance_hosts=true.