Code review comment for lp:~martin-v/zodb/ipv6

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Martin v. Löwis (martin-v) wrote :

Re: DNS. Users currently configure DNS names in zrpc clients to contact ZEO servers, so I guess there is a rationale for that (i.e. users want to use names instead of addresses - in particular with IPv6).

Now, if you allow DNS names, the question is what lookups should you do. The common approach is to look for both AAAA and A, and process them in the order in which the operating system returns them. This is what all client software supporting IPv6 does, so it's also what users expect it to do.

So now that we have one or more IPv6 addresses per name, and one or more IPv4 addresses, which ones should we use? zrpc currently supports connecting to multiple addresses simultaneously, and then taking the one that comes back first. With multiple addresses coming out of DNS, it can speed-up connection establishment when they are tried simultaneously. There is also precedence in other client software doing this, e.g. Apple Safari. As you might have to test each address sequentially, you can just as well do so in parallel.

In addition, it was easier to implement that way. If you think it's undesirable, I can try to come up with a way to do them sequentially.

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