500:
31:
478:
If the client does not close the connection when all of the data it needs has been received, the resources needed to keep the connection open on the server will be unavailable for other clients. How much this affects the server's availability and how long the resources are unavailable depend on the
376:
do not use separate keepalive messages, they just allow multiple requests to use a single connection. However, the default connection timeout of Apache httpd 1.3 and 2.0 is as little as 15 seconds and just 5 seconds for Apache httpd 2.2 and above. The advantage of a short timeout is the ability to
486:
can occur where the client sends a request to the server at the same time that the server closes the TCP connection. A server should send a 408 Request
Timeout status code to the client immediately before closing the connection. When a client receives the 408 status code, after having sent the
469:
but in the words of RFC 7230 "this was found to be impractical for many applications... instead... be conservative when opening multiple connections". These guidelines are intended to improve HTTP response times and avoid congestion. If HTTP pipelining is correctly implemented, there is no
346:
When the server receives this request and generates a response, if it supports keep-alive then it also adds the same above header to the response. Following this, the connection is not dropped, but is instead kept open. When the client sends another request, it uses the same connection.
336:
Since at least late 1995, developers of popular products (browsers, web servers, etc.) using HTTP/1.0, started to add an unofficial extension (to the protocol) named "keep-alive" in order to allow the reuse of a connection for multiple requests/responses.
363:
Since 1997, the various versions of HTTP/1.1 specifications acknowledged the usage of this unofficial extension and included a few caveats regarding the interoperability between HTTP/1.0 (keep-alive) and HTTP/1.1 clients / servers.
541:, the number of simultaneous connections can be customized (per-server, per-proxy, total). Persistent connections time out after 115 seconds (1.92 minutes) of inactivity which is changeable via the configuration.
388:
Keepalive makes it difficult for the client to determine where one response ends and the next response begins, particularly during pipelined HTTP operation. This is a serious problem when
534:
versions 6 and 7 use two persistent connections while version 8 uses six. Persistent connections time out after 60 seconds of inactivity which is changeable via the
Windows Registry.
487:
request, it may open a new connection to the server and re-send the request. Not all clients will re-send the request, and many that do will only do so if the request has an
557:, which establishes a persistent HTTP connection, thereby allowing the underlying TCP connection to be reused, which can result in a significant performance increase.
634:
798:
465:, "a client ought to limit the number of simultaneous open connections that it maintains to a given server". The previous version of the HTTP/1.1 specification
488:
710:
316:
protocol uses the same idea and takes it further to allow multiple concurrent requests/responses to be multiplexed over a single connection.
377:
deliver multiple components of a web page quickly while not consuming resources to run multiple server processes or threads for too long.
870:
840:
Nielssen, Frystyk Henryk; Gettys, James; Baird-Smith, Anselm; Prud’hommeaux, Eric; Wium Lie, Håkon; Lilley, Chris (October 1997),
350:
This will continue until either the client or the server decides that the conversation is over and in this case they omit the
470:
performance benefit to be gained from additional connections, while additional connections may cause issues with congestion.
1061:
642:
674:
664:
769:
433:
609:
277:
451:
305:
1007:
220:
422:
309:
215:
122:
1032:
Hypertext
Transfer Protocol (HTTP/1.1): Message Syntax and Routing, Connection Management, Persistence
382:
312:/responses, as opposed to opening a new connection for every single request/response pair. The newer
165:
944:
756:
745:
734:
714:
251:
826:
393:
246:
1041:
1036:
404:
bit is set at the end of each response so that the client knows where the next response begins.
1046:
841:
241:
418:
414:
236:
986:
812:
698:
596:
524:
372:
In HTTP 1.1, all connections are considered persistent unless declared otherwise. The HTTP
8:
635:"The TCP/IP Guide - HTTP Persistent Connection Establishment, Management and Termination"
520:
905:
576:
447:
270:
575:, which allows out-of-order pipelining of requests and responses, and also predictive
853:
670:
531:
516:
909:
889:
799:"HTTP: What are the relations between pipelining, keep alive and server sent events"
662:
897:
466:
45:
923:
354:
header from the last message sent or, better, they add the keyword "close" to it:
16:
Using a single TCP connection to send and receive multiple HTTP requests/responses
1031:
888:
Fielding, Roy T.; Reschke, Julian (June 2014). Fielding, R.; Reschke, J. (eds.).
566:
462:
440:
156:
663:
David
Gourley; Brian Totty; Marjorie Sayer; Anshu Aggarwal; Sailu Reddy (2002).
340:
If the client supports keep-alive, it adds an additional header to the request:
699:
Hypertext
Transfer Protocol (HTTP/1.1): Message Syntax and Routing, Persistence
483:
392:
cannot be used due to streaming. To solve this problem, HTTP 1.1 introduced a
1055:
857:
508:
499:
263:
141:
151:
146:
113:
108:
103:
98:
93:
83:
78:
73:
64:
966:"How to change the default keep-alive time-out value in Internet Explorer"
666:
HTTP: The
Definitive Guide. (excerpt of chapter: "Persistent Connections")
965:
457:
Errors can be reported without the penalty of closing the TCP connection.
131:
88:
839:
777:
569:, whereby multiple requests can be sent without waiting for a response
901:
136:
199:
194:
189:
184:
179:
174:
538:
512:
890:"Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content"
572:
360:
After that the connection is closed following specified rules.
313:
50:
432:
usage and round-trips because of fewer new connections and
30:
380:
291:
55:
22:
1037:
Persistent
Connection Behavior of Popular Browsers (dated)
597:
Hypertext
Transfer Protocol (HTTP/1.0): Overall Operation
429:
842:"Network Performance Effects of HTTP/1.1, CSS1, and PNG"
871:"How do browsers handle HTTP keepalive race condition?"
1047:
924:"Opera 4.0 Upgrades File Exchange: Includes HTTP 1.1"
711:"Apache HTTP Server 1.3 – KeepAliveTimeout Directive"
813:"HTTP Streaming (or Chunked vs Store & Forward)"
757:
Apache HTTP Server 2.4 – KeepAliveTimeout
Directive
746:
Apache HTTP Server 2.2 – KeepAliveTimeout Directive
735:
Apache HTTP Server 2.0 – KeepAliveTimeout Directive
1053:
887:
689:
694:
692:
503:Schema of multiple vs. persistent connection.
329:Under HTTP 1.0, connections should always be
271:
767:
333:by the server after sending the response.
278:
264:
846:ACM SIGCOMM Computer Communication Review
479:server's architecture and configuration.
498:
308:connection to send and receive multiple
1008:"Requests.AdvancedUsage.SessionObjects"
579:of content before it has been requested
1054:
494:
13:
1010:. ©MMXVIX. A Kenneth Reitz Project
607:
507:All modern web browsers including
14:
1073:
1025:
987:"Network.http.keep-alive.timeout"
544:
200:451 Unavailable for Legal Reasons
473:
304:, is the idea of using a single
29:
1042:Apache HTTPD Keep-Alive Support
1000:
979:
958:
937:
916:
881:
863:
833:
819:
805:
791:
761:
208:Security access control methods
947:. Stevesouders.com. 2008-03-10
750:
739:
728:
703:
656:
627:
601:
590:
467:stated specific maximum values
1:
583:
407:
926:. Opera Software. 2000-03-28
527:use persistent connections.
319:
221:Digest access authentication
7:
1062:Hypertext Transfer Protocol
560:
417:in subsequent requests (no
367:
324:
216:Basic access authentication
10:
1078:
443:of requests and responses.
827:"Chunked Transfer Coding"
383:chunked transfer encoding
252:HTTP parameter pollution
229:Security vulnerabilities
968:. Microsoft. 2007-10-27
669:. O'Reilly Media, inc.
394:chunked transfer coding
343:Connection: keep-alive
247:HTTP response splitting
945:"IE8 speeds things up"
504:
489:idempotent HTTP method
374:persistent connections
242:HTTP request smuggling
502:
463:RFC 7230, section 6.4
302:HTTP connection reuse
294:persistent connection
237:HTTP header injection
175:301 Moved Permanently
166:Response status codes
495:Use in web browsers
780:on January 6, 2010
639:www.tcpipguide.com
610:"HTTP_Connection?"
555:requests.Session()
505:
448:network congestion
357:Connection: close
989:. Mozillazine.org
770:"Httpd/KeepAlive"
768:Multiple (wiki).
553:library contains
532:Internet Explorer
517:Internet Explorer
288:
287:
1069:
1019:
1018:
1016:
1015:
1004:
998:
997:
995:
994:
983:
977:
976:
974:
973:
962:
956:
955:
953:
952:
941:
935:
934:
932:
931:
920:
914:
913:
902:10.17487/RFC7231
894:IETF Datatracker
885:
879:
878:
867:
861:
860:
837:
831:
830:
823:
817:
816:
809:
803:
802:
795:
789:
788:
786:
785:
776:. Archived from
765:
759:
754:
748:
743:
737:
732:
726:
725:
723:
722:
713:. Archived from
707:
701:
696:
687:
686:
684:
683:
660:
654:
653:
651:
650:
641:. Archived from
631:
625:
624:
622:
620:
605:
599:
594:
556:
552:
523:(since 4.0) and
403:
399:
391:
353:
280:
273:
266:
33:
19:
18:
1077:
1076:
1072:
1071:
1070:
1068:
1067:
1066:
1052:
1051:
1028:
1023:
1022:
1013:
1011:
1006:
1005:
1001:
992:
990:
985:
984:
980:
971:
969:
964:
963:
959:
950:
948:
943:
942:
938:
929:
927:
922:
921:
917:
886:
882:
869:
868:
864:
838:
834:
825:
824:
820:
811:
810:
806:
797:
796:
792:
783:
781:
766:
762:
755:
751:
744:
740:
733:
729:
720:
718:
709:
708:
704:
697:
690:
681:
679:
677:
661:
657:
648:
646:
633:
632:
628:
618:
616:
606:
602:
595:
591:
586:
567:HTTP pipelining
563:
554:
550:
547:
497:
476:
452:TCP connections
441:HTTP pipelining
410:
401:
397:
396:that defines a
389:
386:
381:Keepalive with
370:
358:
351:
344:
327:
322:
298:HTTP keep-alive
284:
157:X-Forwarded-For
65:Request methods
17:
12:
11:
5:
1075:
1065:
1064:
1050:
1049:
1044:
1039:
1034:
1027:
1026:External links
1024:
1021:
1020:
999:
978:
957:
936:
915:
880:
877:. Mar 6, 2017.
875:Stack Overflow
862:
832:
818:
804:
790:
760:
749:
738:
727:
702:
688:
675:
655:
626:
600:
588:
587:
585:
582:
581:
580:
570:
562:
559:
546:
545:Implementation
543:
519:(since 4.01),
496:
493:
484:race condition
475:
472:
459:
458:
455:
444:
437:
434:TLS handshakes
426:
409:
406:
390:Content-Length
385:
379:
369:
366:
356:
342:
326:
323:
321:
318:
296:, also called
286:
285:
283:
282:
275:
268:
260:
257:
256:
255:
254:
249:
244:
239:
231:
230:
226:
225:
224:
223:
218:
210:
209:
205:
204:
203:
202:
197:
192:
187:
182:
177:
169:
168:
162:
161:
160:
159:
154:
149:
144:
139:
134:
126:
125:
119:
118:
117:
116:
111:
106:
101:
96:
91:
86:
81:
76:
68:
67:
61:
60:
59:
58:
53:
48:
43:
35:
34:
26:
25:
15:
9:
6:
4:
3:
2:
1074:
1063:
1060:
1059:
1057:
1048:
1045:
1043:
1040:
1038:
1035:
1033:
1030:
1029:
1009:
1003:
988:
982:
967:
961:
946:
940:
925:
919:
911:
907:
903:
899:
895:
891:
884:
876:
872:
866:
859:
855:
851:
847:
843:
836:
828:
822:
814:
808:
800:
794:
779:
775:
771:
764:
758:
753:
747:
742:
736:
731:
717:on 2015-10-26
716:
712:
706:
700:
695:
693:
678:
676:9781565925090
672:
668:
667:
659:
645:on 2017-05-21
644:
640:
636:
630:
615:
614:Google Groups
611:
608:Gildor, Dan.
604:
598:
593:
589:
578:
574:
571:
568:
565:
564:
558:
542:
540:
535:
533:
528:
526:
522:
518:
514:
510:
509:Google Chrome
501:
492:
490:
485:
480:
474:Disadvantages
471:
468:
464:
461:According to
456:
453:
449:
445:
442:
438:
435:
431:
427:
424:
420:
416:
412:
411:
405:
395:
384:
378:
375:
365:
361:
355:
352:"Connection:"
348:
341:
338:
334:
332:
317:
315:
311:
310:HTTP requests
307:
303:
299:
295:
293:
281:
276:
274:
269:
267:
262:
261:
259:
258:
253:
250:
248:
245:
243:
240:
238:
235:
234:
233:
232:
228:
227:
222:
219:
217:
214:
213:
212:
211:
207:
206:
201:
198:
196:
195:404 Not Found
193:
191:
190:403 Forbidden
188:
186:
185:303 See Other
183:
181:
178:
176:
173:
172:
171:
170:
167:
164:
163:
158:
155:
153:
150:
148:
145:
143:
140:
138:
135:
133:
130:
129:
128:
127:
124:
123:Header fields
121:
120:
115:
112:
110:
107:
105:
102:
100:
97:
95:
92:
90:
87:
85:
82:
80:
77:
75:
72:
71:
70:
69:
66:
63:
62:
57:
54:
52:
49:
47:
44:
42:
39:
38:
37:
36:
32:
28:
27:
24:
21:
20:
1012:. Retrieved
1002:
991:. Retrieved
981:
970:. Retrieved
960:
949:. Retrieved
939:
928:. Retrieved
918:
893:
883:
874:
865:
849:
845:
835:
829:. June 1999.
821:
807:
793:
782:. Retrieved
778:the original
773:
763:
752:
741:
730:
719:. Retrieved
715:the original
705:
680:. Retrieved
665:
658:
647:. Retrieved
643:the original
638:
629:
617:. Retrieved
613:
603:
592:
548:
536:
530:By default,
529:
506:
481:
477:
460:
387:
373:
371:
362:
359:
349:
345:
339:
335:
330:
328:
301:
297:
290:
289:
147:HTTP referer
40:
619:17 November
419:handshaking
46:Compression
41:Persistence
1014:2023-04-22
993:2009-07-17
972:2009-07-17
951:2009-07-17
930:2009-07-08
784:2010-01-30
721:2015-01-28
682:2021-10-18
649:2017-12-31
584:References
423:slow start
408:Advantages
402:last-chunk
398:last-chunk
858:0146-4833
549:Python's
400:bit. The
320:Operation
180:302 Found
1056:Category
910:14399078
774:Docforge
561:See also
551:requests
446:Reduced
439:Enables
428:Reduced
413:Reduced
368:HTTP 1.1
325:HTTP 1.0
142:Location
577:pushing
539:Firefox
513:Firefox
482:Also a
450:(fewer
421:and no
415:latency
109:CONNECT
74:OPTIONS
908:
856:
673:
573:HTTP/2
525:Safari
331:closed
314:HTTP/2
132:Cookie
99:DELETE
906:S2CID
852:(4),
521:Opera
300:, or
114:PATCH
104:TRACE
51:HTTPS
854:ISSN
671:ISBN
621:2023
292:HTTP
137:ETag
89:POST
84:HEAD
56:QUIC
23:HTTP
898:doi
537:In
430:CPU
306:TCP
152:DNT
94:PUT
79:GET
1058::
904:.
896:.
892:.
873:.
850:27
848:,
844:,
772:.
691:^
637:.
612:.
515:,
511:,
491:.
454:).
425:).
1017:.
996:.
975:.
954:.
933:.
912:.
900::
815:.
801:.
787:.
724:.
685:.
652:.
623:.
436:.
279:e
272:t
265:v
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
