Re: Proposal: Implement failover on libpq connect level.

But that won't actually help in the case described by Robert: if the master server A failed, the client has no idea if B or C would become the new master.

Unless it actually tries to connect them in turn and check for the result of pg_is_in_recovery().  I think that brings enough complexity for keeping this outside of libpq.  Also think about all the extra flexibility people will likely want to have: number of retries, delay between retries, delay backoff, etc., to the point we'll have to support some sort of client code retry_policy_callback.

For read-only clients you might want to include a number of slave hostnames, and let the connector choose one, but then again you can't achieve load-balancing on the client side, you're better off using round-robin DNS.  To add or remove a slave you only need to update DNS, and not configuration on all the clients.

For the master failover I think a common technique is to just move the floating IP address from the old master to the new one.  This doesn't require touching the DNS record.

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Alex