HTTP pipelining

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Time diagram of non-pipelined vs. pipelined connection

Lua error in package.lua at line 80: module 'Module:Sidebar/configuration' not found. HTTP pipelining is a feature of HTTP/1.1 that allows multiple HTTP requests to be sent over a single TCP connection without waiting for the corresponding responses.[1] HTTP/1.1 requires servers to respond to pipelined requests correctly, with non-pipelined but valid responses even if the server does not support HTTP pipelining. Despite this requirement, many legacy HTTP/1.1 servers do not support pipelining correctly, forcing most HTTP clients not to use HTTP pipelining.

The technique was superseded by multiplexing via HTTP/2,[2] which is supported by most modern browsers.[3]

In HTTP/3, multiplexing is accomplished via QUIC which replaces TCP. This further reduces loading time, as there is no head-of-line blocking even if some packets are lost.

Motivation and limitations

The pipelining of requests results in a dramatic improvement[4] in the loading times of HTML pages, especially over high latency connections such as satellite Internet connections. The speedup is less apparent on broadband connections, as the limitation of HTTP 1.1 still applies: the server must send its responses in the same order that the requests were received—so the entire connection remains first-in-first-out[1] and HOL blocking can occur.

The asynchronous operations of HTTP/2 and SPDY are solution for this.[5] By 2017 most browsers supported HTTP/2 by default which uses multiplexing instead.[2]

Non-idempotent requests such as POST should not be pipelined.[6] Read requests like GET and HEAD can always be pipelined. A sequence of other idempotent requests like PUT and DELETE can be pipelined or not depending on whether requests in the sequence depend on the effect of others.[1]

HTTP pipelining requires both the client and the server to support it. HTTP/1.1 conforming servers are required to produce valid responses to pipelined requests, but may not actually process requests concurrently.[7]

Most pipelining problems happen in HTTP intermediate nodes (hop-by-hop), i.e. in proxy servers, especially in transparent proxy servers (if one of them along the HTTP chain does not handle pipelined requests properly then nothing works as it should).[8]

Using pipelining with HTTP proxy servers is usually not recommended also because the HOL blocking problem may really slow down proxy server responses (as the server responses must be in the same order of the received requests).[1][9]

Example: if a client sends 4 pipelined GET requests to a proxy through a single connection and the first one is not in its cache then the proxy has to forward that request to the destination web server; if the following three requests are instead found in its cache, the proxy has to wait for the web server response, then it has to send it to the client and only then it can send the three cached responses too.

If instead a client opens 4 connections to a proxy and sends 1 GET request per connection (without using pipelining) the proxy can send the three cached responses to client in parallel before the response from server is received, decreasing the overall completion time (because requests are served in parallel with no head-of-line blocking problem).[10] The same advantage exists in HTTP/2 multiplexed streams.

Implementation status

Pipelining was introduced in HTTP/1.1 and was not present in HTTP/1.0.[11]

Implementation in web browsers

Of all the major browsers, only Opera had a fully working implementation that was enabled by default. In other browsers HTTP pipelining was disabled or not implemented.[5]

Implementation in web proxy servers

Most HTTP proxies do not pipeline outgoing requests.[19]

Some HTTP proxies, including transparent HTTP proxies, may manage pipelined requests very badly (e.g. by mixing up the order of pipelined responses).[20]

Some versions of the Squid web proxy will pipeline up to two outgoing requests. This functionality has been disabled by default and needs to be manually enabled for "bandwidth management and access logging reasons".[21] Squid supports multiple requests from clients.

The Polipo proxy pipelines outgoing requests.[22]

Tempesta FW, an open source application delivery controller,[23] also pipelines requests to backend servers.[24]

Other implementations

The libwww library made by the World Wide Web Consortium (W3C), supports pipelining since version 5.1 released at 18 February 1997.[25]

Other application development libraries that support HTTP pipelining include:

  • Perl modules providing client support for HTTP pipelining are HTTP::Async and the LWPng (libwww-perl New Generation) library.[26]
  • The Microsoft .NET Framework 3.5 supports HTTP pipelining in the module System.Net.HttpWebRequest.[27]
  • Qt class QNetworkRequest, introduced in 4.4.[28]

Some other applications currently exploiting pipelining are:

Testing tools which support HTTP pipelining include:

See also

References

Page Template:Reflist/styles.css has no content.

  1. ^ a b c d Page Module:Citation/CS1/styles.css has no content.Fielding, R.; Reschke, J. (2014). Fielding, R.; Reschke, J. (eds.). "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing: Pipelining". ietf.org. doi:10.17487/RFC7230. Retrieved 2014-07-24. {{cite journal}}: Cite journal requires |journal= (help)
  2. ^ a b Page Module:Citation/CS1/styles.css has no content."Revision 1330814 | Connection management in HTTP/1.x | MDN". MDN Web Docs. Archived from the original on 2018-03-19. Retrieved 2018-03-19.
  3. ^ Page Module:Citation/CS1/styles.css has no content."HTTP2 browser support". Retrieved March 9, 2017.
  4. ^ Page Module:Citation/CS1/styles.css has no content.Nielsen, Henrik Frystyk; Gettys, Jim; Baird-Smith, Anselm; Prud'hommeaux, Eric; Lie, Håkon Wium; Lilley, Chris (24 June 1997). "Network Performance Effects of HTTP/1.1, CSS1, and PNG". World Wide Web Consortium. Retrieved 14 January 2010.
  5. ^ a b Page Module:Citation/CS1/styles.css has no content.Willis, Nathan (18 November 2009). "Reducing HTTP latency with SPDY". LWN.net.
  6. ^ Page Module:Citation/CS1/styles.css has no content."Connections". w3.org.
  7. ^ Page Module:Citation/CS1/styles.css has no content."HTTP/1.1 Pipelining FAQ'".
  8. ^ Page Module:Citation/CS1/styles.css has no content.Mark Nottingham (March 14, 2011). "Making HTTP Pipelining Usable on the Open Web". Retrieved October 16, 2021.
  9. ^ a b Page Module:Citation/CS1/styles.css has no content."Wayback link of 'Windows Internet Explorer 8 Expert Zone Chat (August 14, 2008)'". Microsoft. August 14, 2008. Archived from the original on December 4, 2010. Retrieved May 10, 2012.
  10. ^ Page Module:Citation/CS1/styles.css has no content.Fielding, R.; Reschke, J. (2014). Fielding, R.; Reschke, J. (eds.). "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing: Concurrency". ietf.org. doi:10.17487/RFC7230. Retrieved 2014-07-24. {{cite journal}}: Cite journal requires |journal= (help)
  11. ^ Page Module:Citation/CS1/styles.css has no content."Key Differences between HTTP/1.0 and HTTP/1.1". Archived from the original on 2016-04-24. Retrieved 2016-04-16.
  12. ^ Page Module:Citation/CS1/styles.css has no content."Internet Explorer and Connection Limits". IEBlog. Retrieved 2016-11-14.
  13. ^ Firefox 54 Release Notes
  14. ^ Page Module:Citation/CS1/styles.css has no content."Bug 264354: Enable HTTP pipelining by default". Mozilla. Retrieved September 16, 2011.
  15. ^ Page Module:Citation/CS1/styles.css has no content."Source code – nsHttpConnection.cpp". Firefox source code. Mozilla. May 7, 2010. Retrieved December 5, 2010.
  16. ^ Page Module:Citation/CS1/styles.css has no content.Emir Arian. Internet Communication: Protocols and related subjects. Retrieved 2021-10-16.
  17. ^ HTTP Pipelining - The Chromium Projects
  18. ^ Page Module:Citation/CS1/styles.css has no content."HTTP/1 Pipelining support has been removed in Firefox 54 - Pale Moon forum". forum.palemoon.org. Retrieved 2018-06-07.
  19. ^ Page Module:Citation/CS1/styles.css has no content.Mark Nottingham (June 20, 2007). "The State of Proxy Caching". Retrieved May 16, 2009.
  20. ^ Page Module:Citation/CS1/styles.css has no content.Mark Nottingham (July 11, 2011). "What proxies must do". Mark Nottingham. Retrieved October 16, 2021.
  21. ^ Page Module:Citation/CS1/styles.css has no content."squid : pipeline_prefetch configuration directive". Squid. November 9, 2009. Retrieved December 1, 2009.
  22. ^ Page Module:Citation/CS1/styles.css has no content."Polipo — a caching web proxy". Juliusz Chroboczek. September 18, 2009. Retrieved November 12, 2009.
  23. ^ Page Module:Citation/CS1/styles.css has no content."Tempesta FW — a Linux Application Delivery Controller". GitHub. Retrieved March 29, 2018.
  24. ^ Page Module:Citation/CS1/styles.css has no content."Servers: Tempesta's side - tempesta-tech/tempesta Wiki". Tempesta Technologies INC. August 1, 2017. Retrieved March 29, 2018.
  25. ^ Page Module:Citation/CS1/styles.css has no content.Kahan, José (June 7, 2002). "Change History of libwww". World Wide Web Consortium. Retrieved August 3, 2010.
  26. ^ Page Module:Citation/CS1/styles.css has no content."Using HTTP::Async for Parallel HTTP Requests (Colin Bradford)" (PDF). Archived from the original (PDF) on 2012-03-10. Retrieved 2010-08-03.
  27. ^ System.Net.HttpWebRequest & pipelining
  28. ^ QNetworkRequest Class Reference Script error: No such module "webarchive"., Nokia QT documentation
  29. ^ Pipelined HTTP GET utility
  30. ^ Curl pipelining explanation Script error: No such module "webarchive"., Curl developer documentation
  31. ^ Curl pipelining removal announcementScript error: No such module "webarchive".
  32. ^ Page Module:Citation/CS1/styles.css has no content.C. Michael Pilato; Ben Collins-Sussman; Brian W. Fitzpatrick (2008). Version Control with Subversion. O'Reilly Media. p. 238. ISBN 978-0-596-51033-6.
  33. ^ Page Module:Citation/CS1/styles.css has no content.Justin R. Erenkrantz (2007). "Subversion: Powerful New Toys" (PDF).
  34. ^ Page Module:Citation/CS1/styles.css has no content."HTTP/HTTPS messages". Microsoft TechNet. January 21, 2005.
  35. ^ How CICS Web support handles pipelining
  36. ^ Page Module:Citation/CS1/styles.css has no content."HTTP Website". Archived from the original on 2012-06-08. Retrieved 2010-10-01.
  37. ^ Page Module:Citation/CS1/styles.css has no content."Library http". Retrieved 2024-11-12.
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