My view is a) the server was unavailable for this request due to all the other requests it’s currently dealing with b) the connection was not idle, the client is not at fault.
B. > On 18 Apr 2019, at 22:03, Done Collectively <sans...@inator.biz> wrote: > > Any reason 408 would be undesirable? > > https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/408 > > > On Thu, Apr 18, 2019 at 10:37 AM Robert Newson <rnew...@apache.org> wrote: > >> 503 imo. >> >> -- >> Robert Samuel Newson >> rnew...@apache.org >> >> On Thu, 18 Apr 2019, at 18:24, Adam Kocoloski wrote: >>> Yes, we should. Currently it’s a 500, maybe there’s something more >> appropriate: >>> >>> >> https://github.com/apache/couchdb/blob/8ef42f7241f8788afc1b6e7255ce78ce5d5ea5c3/src/chttpd/src/chttpd.erl#L947-L949 >>> >>> Adam >>> >>>> On Apr 18, 2019, at 12:50 PM, Joan Touzet <woh...@apache.org> wrote: >>>> >>>> What happens when it turns out the client *hasn't* timed out and we >>>> just...hang up on them? Should we consider at least trying to send back >>>> some sort of HTTP status code? >>>> >>>> -Joan >>>> >>>> On 2019-04-18 10:58, Garren Smith wrote: >>>>> I'm +1 on this. With partition queries, we added a few more timeouts >> that >>>>> can be enabled which Cloudant enable. So having the ability to shed >> old >>>>> requests when these timeouts get hit would be great. >>>>> >>>>> Cheers >>>>> Garren >>>>> >>>>> On Tue, Apr 16, 2019 at 2:41 AM Adam Kocoloski <kocol...@apache.org> >> wrote: >>>>> >>>>>> Hi all, >>>>>> >>>>>> For once, I’m coming to you with a topic that is not strictly about >>>>>> FoundationDB :) >>>>>> >>>>>> CouchDB offers a few config settings (some of them undocumented) to >> put a >>>>>> limit on how long the server is allowed to take to generate a >> response. The >>>>>> trouble with many of these timeouts is that, when they fire, they do >> not >>>>>> actually clean up all of the work that they initiated. A couple of >> examples: >>>>>> >>>>>> - Each HTTP response coordinated by the “fabric” application spawns >>>>>> several ephemeral processes via “rexi" on different nodes in the >> cluster to >>>>>> retrieve data and send it back to the process coordinating the >> response. If >>>>>> the request timeout fires, the coordinating process will be killed >> off, but >>>>>> the ephemeral workers might not be. In a healthy cluster they’ll >> exit on >>>>>> their own when they finish their jobs, but there are conditions >> under which >>>>>> they can sit around for extended periods of time waiting for an >> overloaded >>>>>> gen_server (e.g. couch_server) to respond. >>>>>> >>>>>> - Those named gen_servers (like couch_server) responsible for >> serializing >>>>>> access to important data structures will dutifully process messages >>>>>> received from old requests without any regard for (of even knowledge >> of) >>>>>> the fact that the client that sent the message timed out long ago. >> This can >>>>>> lead to a sort of death spiral in which the gen_server is ultimately >>>>>> spending ~all of its time serving dead clients and every client is >> timing >>>>>> out. >>>>>> >>>>>> I’d like to see us introduce a documented maximum request duration >> for all >>>>>> requests except the _changes feed, and then use that information to >> aid in >>>>>> load shedding throughout the stack. We can audit the codebase for >>>>>> gen_server calls with long timeouts (I know of a few on the critical >> path >>>>>> that set their timeouts to `infinity`) and we can design servers that >>>>>> efficiently drop old requests, knowing that the client who made the >> request >>>>>> must have timed out. A couple of topics for discussion: >>>>>> >>>>>> - the “gen_server that sheds old requests” is a very generic >> pattern, one >>>>>> that seems like it could be well-suited to its own behaviour. A >> cursory >>>>>> search of the internet didn’t turn up any prior art here, which >> surprises >>>>>> me a bit. I’m wondering if this is worth bringing up with the broader >>>>>> Erlang community. >>>>>> >>>>>> - setting and enforcing timeouts is a healthy pattern for read-only >>>>>> requests as it gives a lot more feedback to clients about the health >> of the >>>>>> server. When it comes to updates things are a little bit more muddy, >> just >>>>>> because there remains a chance that an update can be committed, but >> the >>>>>> caller times out before learning of the successful commit. We should >> try to >>>>>> minimize the likelihood of that occurring. >>>>>> >>>>>> Cheers, Adam >>>>>> >>>>>> P.S. I did say that this wasn’t _strictly_ about FoundationDB, but of >>>>>> course FDB has a hard 5 second limit on all transactions, so it is a >> bit of >>>>>> a forcing function :).Even putting FoundationDB aside, I would still >> argue >>>>>> to pursue this path based on our Ops experience with the current >> codebase. >>>>> >>>> >>> >>> >>
