Date: Fri, 18 Feb 2005 17:43:23 +0300 From: Deomid Ryabkov <myself@rojer.pp.ru> To: Peter Edwards <peadar.edwards@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: occasional ECONNREFUSED when connect()ing. Message-ID: <4215FF0B.6060307@rojer.pp.ru> In-Reply-To: <34cb7c8405021806386fb874ee@mail.gmail.com> References: <4215EB31.8020107@rojer.pp.ru> <34cb7c8405021806386fb874ee@mail.gmail.com>
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This is a cryptographically signed message in MIME format. --------------ms070607020207090709080309 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit guys, there is _source_ of the server at the end of my post! there are no threads nor forks and backlog is set to 511 (Apache's default value). and client always waits for rrequst to complete before sending a new one. Peter Edwards wrote: >On Fri, 18 Feb 2005 16:18:41 +0300, Deomid Ryabkov <myself@rojer.pp.ru> wrote: > > >>I have a strange case of occasional refused connect()'s. >>The system is running 4.10-STABLE. >> >>This was originally reported by one of our developers. >>The test script he provided is a simple Perl script that repeatedly >>fetches an URL >>from Apache running on this same server. >>In the run of 2000 iterations, there are 5-10 random errors fetching the >>URL. >>After further investigation and digging, I uncovered the true cause of >>the error: >>connect() returning ECONNREFUSED. >>To see if this was somehow related to Apache, I wrote my own simple >>server that >>accept()'s a connection, read()'s what supposed to be request and >>write()'s a stereotypic reply, >>thus resembling an HTTP request/reply conversation. >>The number of sporadically occuring connect() errors has increased somewhat, >>maybe due to quicker turnaround of my stub-server. >>The question is - why do connections get refused at all? >>I can think of no valid reasons... >> >> > >Here's one: >In your stub server, what do you set the backlog to in the call to listen(2)? > >By the time you get the file descriptor for the new call from >accept(), the kernel has already established the TCP/IP connection, >and is maintaining state (ie, using resources) for it > >If you take a while dealing with this new call, (starting a thread, >forking, or even processing the connection), then by the time you >invoke accept() again, any number of clients may have attempted to >connect to you, and the kernel needs to maintain state for every >connection that has been requested. > >The backlog on the listen call indicates how many of these connections >the kernel should hold on to: If the number of unaccept()ed >connections reaches the backlog, you'll start to get ECONREFUSED >errors at the client. If your stub server is single-threaded, this'll >be pretty much guaranteed to happen if the number of clients exceeds >the backlog on ths server's listening socket. > >HTH, >peadar. > -- Deomid Ryabkov aka Rojer myself@rojer.pp.ru rojer@sysadmins.ru ICQ: 8025844 --------------ms070607020207090709080309 Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIJIzCC AuwwggJVoAMCAQICAwwKdjANBgkqhkiG9w0BAQQFADBiMQswCQYDVQQGEwJaQTElMCMGA1UE ChMcVGhhd3RlIENvbnN1bHRpbmcgKFB0eSkgTHRkLjEsMCoGA1UEAxMjVGhhd3RlIFBlcnNv bmFsIEZyZWVtYWlsIElzc3VpbmcgQ0EwHhcNMDQwMzMxMjIxODA5WhcNMDUwMzMxMjIxODA5 WjBfMRAwDgYDVQQEEwdSeWFia292MQ8wDQYDVQQqEwZEZW9taWQxFzAVBgNVBAMTDkRlb21p ZCBSeWFia292MSEwHwYJKoZIhvcNAQkBFhJteXNlbGZAcm9qZXIucHAucnUwggEiMA0GCSqG SIb3DQEBAQUAA4IBDwAwggEKAoIBAQDBxXgFP/1lZDqp0dzUDzR5IBb7aKki6TD+HMMkRjtP IOcaNHsfoDer9RFrFICoxNQZF86iopYFVYr7msgB9y2dKZTRQQoOA72lFrOyH3sgrztx/3LL axEsihA2cxcrglrIgPEm6FF2aabbKVpSdeslMCDPBr0auAm0QLo8ch9c5j0vuQUBrs8TKU6f 6YZLNO2Sk/fPZP2kfJEkXyZhkU6wq3ER1CHq2qgfNpW2Ni7Kuv/eYI/CV1BGgm37ZPubOyxI LNiRUGT0pv0wocrCIehKqoI1uFPZgGS0ANYTqPJQSdjlSzMGQJjT510PNDJnDfKOvLhcadD+ 6gSL/ovNM/LPAgMBAAGjLzAtMB0GA1UdEQQWMBSBEm15c2VsZkByb2plci5wcC5ydTAMBgNV HRMBAf8EAjAAMA0GCSqGSIb3DQEBBAUAA4GBACunC6DhFX4I6Nvdy/UevjSd3VmKWPRmqwoR l0RXvuI/JVyPO9KHGqxCMpRu7ArJz7d8ShPVs5kynysrB+Nm6/fwWjeaW21+gViojeO9gGP6 Np/LeMIqkqSYMoElq7Feqh/3qp7a/UxuofFtAW9V/2tRunxaPo4/WOxcdcmdcC86MIIC7DCC AlWgAwIBAgIDDAp2MA0GCSqGSIb3DQEBBAUAMGIxCzAJBgNVBAYTAlpBMSUwIwYDVQQKExxU aGF3dGUgQ29uc3VsdGluZyAoUHR5KSBMdGQuMSwwKgYDVQQDEyNUaGF3dGUgUGVyc29uYWwg RnJlZW1haWwgSXNzdWluZyBDQTAeFw0wNDAzMzEyMjE4MDlaFw0wNTAzMzEyMjE4MDlaMF8x EDAOBgNVBAQTB1J5YWJrb3YxDzANBgNVBCoTBkRlb21pZDEXMBUGA1UEAxMORGVvbWlkIFJ5 YWJrb3YxITAfBgkqhkiG9w0BCQEWEm15c2VsZkByb2plci5wcC5ydTCCASIwDQYJKoZIhvcN AQEBBQADggEPADCCAQoCggEBAMHFeAU//WVkOqnR3NQPNHkgFvtoqSLpMP4cwyRGO08g5xo0 ex+gN6v1EWsUgKjE1BkXzqKilgVVivuayAH3LZ0plNFBCg4DvaUWs7IfeyCvO3H/cstrESyK EDZzFyuCWsiA8SboUXZpptspWlJ16yUwIM8GvRq4CbRAujxyH1zmPS+5BQGuzxMpTp/phks0 7ZKT989k/aR8kSRfJmGRTrCrcRHUIeraqB82lbY2Lsq6/95gj8JXUEaCbftk+5s7LEgs2JFQ ZPSm/TChysIh6EqqgjW4U9mAZLQA1hOo8lBJ2OVLMwZAmNPnXQ80MmcN8o68uFxp0P7qBIv+ i80z8s8CAwEAAaMvMC0wHQYDVR0RBBYwFIESbXlzZWxmQHJvamVyLnBwLnJ1MAwGA1UdEwEB /wQCMAAwDQYJKoZIhvcNAQEEBQADgYEAK6cLoOEVfgjo293L9R6+NJ3dWYpY9GarChGXRFe+ 4j8lXI870ocarEIylG7sCsnPt3xKE9WzmTKfKysH42br9/BaN5pbbX6BWKiN472AY/o2n8t4 wiqSpJgygSWrsV6qH/eqntr9TG6h8W0Bb1X/a1G6fFo+jj9Y7Fx1yZ1wLzowggM/MIICqKAD AgECAgENMA0GCSqGSIb3DQEBBQUAMIHRMQswCQYDVQQGEwJaQTEVMBMGA1UECBMMV2VzdGVy biBDYXBlMRIwEAYDVQQHEwlDYXBlIFRvd24xGjAYBgNVBAoTEVRoYXd0ZSBDb25zdWx0aW5n MSgwJgYDVQQLEx9DZXJ0aWZpY2F0aW9uIFNlcnZpY2VzIERpdmlzaW9uMSQwIgYDVQQDExtU aGF3dGUgUGVyc29uYWwgRnJlZW1haWwgQ0ExKzApBgkqhkiG9w0BCQEWHHBlcnNvbmFsLWZy ZWVtYWlsQHRoYXd0ZS5jb20wHhcNMDMwNzE3MDAwMDAwWhcNMTMwNzE2MjM1OTU5WjBiMQsw CQYDVQQGEwJaQTElMCMGA1UEChMcVGhhd3RlIENvbnN1bHRpbmcgKFB0eSkgTHRkLjEsMCoG A1UEAxMjVGhhd3RlIFBlcnNvbmFsIEZyZWVtYWlsIElzc3VpbmcgQ0EwgZ8wDQYJKoZIhvcN AQEBBQADgY0AMIGJAoGBAMSmPFVzVftOucqZWh5owHUEcJ3f6f+jHuy9zfVb8hp2vX8MOmHy v1HOAdTlUAow1wJjWiyJFXCO3cnwK4Vaqj9xVsuvPAsH5/EfkTYkKhPPK9Xzgnc9A74r/rsY Pge/QIACZNenprufZdHFKlSFD0gEf6e20TxhBEAeZBlyYLf7AgMBAAGjgZQwgZEwEgYDVR0T AQH/BAgwBgEB/wIBADBDBgNVHR8EPDA6MDigNqA0hjJodHRwOi8vY3JsLnRoYXd0ZS5jb20v VGhhd3RlUGVyc29uYWxGcmVlbWFpbENBLmNybDALBgNVHQ8EBAMCAQYwKQYDVR0RBCIwIKQe MBwxGjAYBgNVBAMTEVByaXZhdGVMYWJlbDItMTM4MA0GCSqGSIb3DQEBBQUAA4GBAEiM0VCD 6gsuzA2jZqxnD3+vrL7CF6FDlpSdf0whuPg2H6otnzYvwPQcUCCTcDz9reFhYsPZOhl+hLGZ GwDFGguCdJ4lUJRix9sncVcljd2pnDmOjCBPZV+V2vf3h9bGCE6u9uo05RAaWzVNd+NWIXiC 3CEZNd4ksdMdRv9dX2VPMYIDOzCCAzcCAQEwaTBiMQswCQYDVQQGEwJaQTElMCMGA1UEChMc VGhhd3RlIENvbnN1bHRpbmcgKFB0eSkgTHRkLjEsMCoGA1UEAxMjVGhhd3RlIFBlcnNvbmFs IEZyZWVtYWlsIElzc3VpbmcgQ0ECAwwKdjAJBgUrDgMCGgUAoIIBpzAYBgkqhkiG9w0BCQMx CwYJKoZIhvcNAQcBMBwGCSqGSIb3DQEJBTEPFw0wNTAyMTgxNDQzMjNaMCMGCSqGSIb3DQEJ BDEWBBS57qfYXdl8fSkkr+7rfgtLginx3zBSBgkqhkiG9w0BCQ8xRTBDMAoGCCqGSIb3DQMH MA4GCCqGSIb3DQMCAgIAgDANBggqhkiG9w0DAgIBQDAHBgUrDgMCBzANBggqhkiG9w0DAgIB KDB4BgkrBgEEAYI3EAQxazBpMGIxCzAJBgNVBAYTAlpBMSUwIwYDVQQKExxUaGF3dGUgQ29u c3VsdGluZyAoUHR5KSBMdGQuMSwwKgYDVQQDEyNUaGF3dGUgUGVyc29uYWwgRnJlZW1haWwg SXNzdWluZyBDQQIDDAp2MHoGCyqGSIb3DQEJEAILMWugaTBiMQswCQYDVQQGEwJaQTElMCMG A1UEChMcVGhhd3RlIENvbnN1bHRpbmcgKFB0eSkgTHRkLjEsMCoGA1UEAxMjVGhhd3RlIFBl cnNvbmFsIEZyZWVtYWlsIElzc3VpbmcgQ0ECAwwKdjANBgkqhkiG9w0BAQEFAASCAQAd+DDH fzTiG19+K39tdDuBft9f1h924D+kNpXj7/IEmFXdKsqLzWhgoScwYCF/VWgEu9LBllGpKe5n yZLRDOxIOWuVmHXK2vJ1RmmN4EQZUF/eCo/UeMVjaxPXXhgg6dSEDefY8M3jDlxfNHfpTMS2 P+dS7HlZA53KHuZOC2c28XSEkEAwA+ph4L9PMHAyx3B3dSxS46HoW3CNb63tmlE4IzcsuWfS Flhdakj0mH1B1Bh8bfKzOj9Ln+E4Tr5fUzkLutFho6bIgNT7AgcMihtwsQlK8qhcxxjeaVXa JNQs/anDDQcdlQW0gRQHcDpHuYR4DzJkwzxVjye82uh6g/HuAAAAAAAA --------------ms070607020207090709080309--
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