I've just built a new PostgreSQL server for my employers, which is happily replicating using WALs. I'm now left with the problem of verifying its performance. One nice way which came up in conversation is to break replication with the slave caught up and then direct all production traffic to both servers, discarding the responses from the new server and returning those from the current one to the clients. Once we're sure performance is OK, we re-sync the slave and can fail over with confidence. Bliss.

This would require a TCP proxy capable of opening two outgoing connections for each incoming one, and discarding the data returned from one of them, which is a tricky thing to google for, it seems. Do the assembled brains know of such a thing, before I dive into libevent and write one?