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RE: Massive HTTP/2 parallel requests

From: Molina <>
Date: Wed, 2 Mar 2016 15:30:28 +0100

The results of curl —version are:

curl 7.47.1 (x86_64-apple-darwin15.3.0) libcurl/7.47.1 OpenSSL/1.0.2f zlib/1.2.5 nghttp2/1.7.0
Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtsp smb smbs smtp smtps telnet tftp
Features: IPv6 Largefile NTLM NTLM_WB SSL libz TLS-SRP HTTP2 UnixSockets

Concerning the server, I’m running an apache with mod_http2 enabled and the following HTTP/2-related configuration:

LoadModule http2_module modules/
<IfModule http2_module>
  Protocols h2c http/1.1
  LogLevel http2:info

I performed this very morning another test adding the following line: H2MaxSessionStreams 1000000
I was just to make sure that the number of streams is higher than the number of parallel downloads for my test (1024). I realised looking at the logs that all my requests fit in the pipe, but still files are downloaded in 64-stream blocks! If I try with normal HTPP/1.1 connections the total test is around 20 times faster than this way.

On a second test I set the following parameters:
  curl_multi_setopt(multi_handle, CURLMOPT_MAX_TOTAL_CONNECTIONS, 10);
  curl_multi_setopt(multi_handle, CURLMOPT_MAX_HOST_CONNECTIONS, 10);

And what happens is quite annoying: it opened the connection 0 for the file 1, and consecutive connections 1-9 for files 2-10. The rest 11-1024 where attached to connection 0, so that when connections 1-9 finished (with only one request) they were not reused.

Any clues?

> Date: Wed, 2 Mar 2016 11:42:59 +0000
> From: Lucas Pardue <>
> To: libcurl development <>
> Subject: RE: Massive HTTP/2 parallel requests
> Message-ID: <7CF7F94CB496BF4FAB1676F375F9666A2A79C174_at_bgb01xud1012>
> Content-Type: text/plain; charset="utf-8"
> Hello,
> What version of libcurl are you using? There were some issues with libcurl's multiplexing reported in January that were fixed, see
> Note that the maximum number of concurrent streams is directional ( It sounds like perhaps the server is restricting you to only 64 concurrent client-initiated streams per connection. Can you tell us the value the server is using? If you don't have access to server config a packet trace of the SETTINGS frame (or dump in client code) will let us know.
> Regards
> Lucas

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Received on 2016-03-02