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Open new HTTP/2 connections when stream space is exhausted. #283
Description
http://http2.github.io/http2-spec/index.html#StreamIdentifiers "Long-lived connections can result in an endpoint exhausting the available range of stream identifiers. A client that is unable to establish a new stream identifier can establish a new connection for new streams. "
Somewhat related to #282
Activity
gdhameeja commentedon Sep 7, 2019
I would like to work on this.
Fix encode#283
florimondmanca commentedon Sep 21, 2019
Is this actually an issue for us?
h2sets itsHIGHEST_ALLOWED_STREAM_IDto 2^31 - 1, which is ~2^30 streams we can open (client-side stream IDs are always odd), i.e. about 1M streams. Are we ever going to open that many connections, and still want to open more after that point? Surely theMAX_CONCURRENT_STREAMSlimit imposed byh2(100 by default) will hit us before that.sethmlarson commentedon Sep 21, 2019
Stream space is number of requests on a single connection, since each request requires its own stream. The concurrent streams limit is the number of requests you're allowed to have outstanding before making a new request.
florimondmanca commentedon Sep 21, 2019
OK, I think we've got a shared understanding then.
What made me think about whether this is a practical issue is this:
https://github.com/python-hyper/hyper-h2/blob/385ced7d30a7ccb9b3f163f1bc4e90cf2f4ee184/h2/connection.py#L641-L651
Essentially, we can only get a
NoAvailableStreamIDErrorwhen theHIGHEST_ALLOWED_STREAM_IDis reached, which is when we're making 1 million requests to the same host via a single connection. How likely is that to happen? Or maybe I'm completely missing something?sethmlarson commentedon Sep 21, 2019
It's not likely in everyday usage but it's a part of being a consumer of the
h2library. I can see it eventually happening for servers with connections to external APIs.ojii commentedon Feb 18, 2020
We do about 1 million requests per day to a single host (APNS) in our application, so to me it doesn't seem too unrealistic to hit this limit, if a connection stays open for some time.
lovelydinosaur commentedon Apr 30, 2020
Believe this to now be resolved in the 0.13.dev0 pre-release.