Thanks Alex, this is very helpful. Another interesting fact is that I can't reproduce this issue if squid has no other traffic except my testing requests. But it's easy to reproduce when server has other traffic.
The problem is that with other traffic I can't provide the whole log file with debug ALL,7 enabled because it has other requests. So I tried to select only parts related to my test request (this is ALL,7): https://www.dropbox.com/s/udzeipeerf5o38t/squid_retry_logs.tgz?dl=1 On Tue, Nov 28, 2017 at 7:32 AM, Alex Rousskov < rouss...@measurement-factory.com> wrote: > On 11/27/2017 05:19 PM, Ivan Larionov wrote: > > > I see retries only when squid config has 2 parents. If I comment out > > everything related to "newproxy" I can't reproduce this behavior anymore. > > The posted logs are not detailed enough to confirm or deny that IMO, but > I suspect that you are dealing with at least one bug. > > > > https://wiki.squid-cache.org/SquidFaq/InnerWorkings#When_ > does_Squid_re-forward_a_client_request.3F > > > >> Squid does not try to re-forward a request if at least one of the > following conditions is true: > >> > >> The number of forwarding attempts exceeded forward_max_tries. For > >> example, if you set forward_max_tries to 1 (one), then no requests > >> will be re-forwarded. > > > AFAICT, there is an off-by-one bug in Squid that violates the above: > > > if (n_tries > Config.forward_max_tries) > > return false; > > The n_tries counter is incremented before Squid makes a request > forwarding attempt. With n_tries and Config.forward_max_tries both set > to 1, the quoted FwdState::checkRetry() code will not prevent > re-forwarding. There is a similar problem in FwdState::reforward(). This > reasoning needs confirmation/testing. > > Please note that simply changing the ">" operator to ">=" may break > other things in a difficult-to-detect-by-simple-tests ways. The correct > fix may be more complex than it looks and may involve making policy > decisions regarding forward_max_tries meaning. The best fix would remove > checkRetry() and reforward() duplication. This code is difficult to work > with; many related code names are misleading. > > > >> Squid has no alternative destinations to try. Please note that > >> alternative destinations may include multiple next hop IP addresses > >> and multiple peers. > > The fact that Squid sends two requests to the same peer with only one > peer address selected suggests that Squid is retrying a failed > persistent connection rather than re-forwarding after receiving a bad > response. Again, the logs are not detailed enough to distinguish the two > cases. I can only see that a single peer/destination address was > selected (not two), which is correct/expected behavior. I cannot see > what happened next with sufficient detail. > > Going forward, you have several options, including: > > A. Post a link to compressed ALL,7+ logs to confirm bug(s). > B. Fix the broken condition(s) in FwdState. See above. > > HTH, > > Alex. > > > > 2017/11/27 15:53:40.542| 5,2| TcpAcceptor.cc(220) doAccept: New > connection on FD 15 > > 2017/11/27 15:53:40.542| 5,2| TcpAcceptor.cc(295) acceptNext: connection > > on local=0.0.0.0:3128 <http://0.0.0.0:3128> remote=[::] FD 15 flags=9 > > 2017/11/27 15:53:40.543| 11,2| client_side.cc(2372) parseHttpRequest: > > HTTP Client local=127.0.0.1:3128 <http://127.0.0.1:3128> > > remote=127.0.0.1:53798 <http://127.0.0.1:53798> FD 45 flags=1 > > 2017/11/27 15:53:40.543| 11,2| client_side.cc(2373) parseHttpRequest: > > HTTP Client REQUEST: > > --------- > > GET http://HOST:12345/ HTTP/1.1 > > Host: HOST:12345 > > User-Agent: curl/7.51.0 > > Accept: */* > > Proxy-Connection: Keep-Alive > > > > > > ---------- > > 2017/11/27 15:53:40.543| 85,2| client_side_request.cc(745) > > clientAccessCheckDone: The request GET http://HOST:12345/ is ALLOWED; > > last ACL checked: localhost > > 2017/11/27 15:53:40.543| 85,2| client_side_request.cc(721) > > clientAccessCheck2: No adapted_http_access configuration. default: ALLOW > > 2017/11/27 15:53:40.543| 85,2| client_side_request.cc(745) > > clientAccessCheckDone: The request GET http://HOST:12345/ is ALLOWED; > > last ACL checked: localhost > > 2017/11/27 15:53:40.543| 17,2| FwdState.cc(133) FwdState: Forwarding > > client request local=127.0.0.1:3128 <http://127.0.0.1:3128> > > remote=127.0.0.1:53798 <http://127.0.0.1:53798> FD 45 flags=1, > > url=http://HOST:12345/ > > 2017/11/27 15:53:40.543| 44,2| peer_select.cc(258) peerSelectDnsPaths: > > Find IP destination for: http://HOST:12345/' via 127.0.0.1 > > 2017/11/27 15:53:40.543| 44,2| peer_select.cc(280) peerSelectDnsPaths: > > Found sources for 'http://HOST:12345/' > > 2017/11/27 15:53:40.543| 44,2| peer_select.cc(281) peerSelectDnsPaths: > > always_direct = DENIED > > 2017/11/27 15:53:40.543| 44,2| peer_select.cc(282) peerSelectDnsPaths: > > never_direct = ALLOWED > > 2017/11/27 15:53:40.543| 44,2| peer_select.cc(292) peerSelectDnsPaths: > > cache_peer = local=127.0.0.3 remote=127.0.0.1:18070 > > <http://127.0.0.1:18070> flags=1 > > 2017/11/27 15:53:40.543| 44,2| peer_select.cc(295) peerSelectDnsPaths: > > timedout = 0 > > 2017/11/27 15:53:40.543| 11,2| http.cc(2229) sendRequest: HTTP Server > > local=127.0.0.3:57091 <http://127.0.0.3:57091> remote=127.0.0.1:18070 > > <http://127.0.0.1:18070> FD 40 flags=1 > > 2017/11/27 15:53:40.543| 11,2| http.cc(2230) sendRequest: HTTP Server > > REQUEST: > > --------- > > GET http://HOST:12345/ HTTP/1.1 > > User-Agent: curl/7.51.0 > > Accept: */* > > Host: HOST:12345 > > Cache-Control: max-age=259200 > > Connection: keep-alive > > > > > > ---------- > > > > [SKIPPED 40 seconds until parent closes TCP connection with FIN,ACK] > > > > 2017/11/27 15:54:20.627| 11,2| http.cc(1299) continueAfterParsingHeader: > > WARNING: HTTP: Invalid Response: No object data received for > > http://HOST:12345/ AKA HOST/ > > 2017/11/27 15:54:20.627| 17,2| FwdState.cc(655) > > handleUnregisteredServerEnd: self=0x3e31838*2 err=0x409b338 > > http://HOST:12345/ > > 2017/11/27 15:54:20.627| 11,2| http.cc(2229) sendRequest: HTTP Server > > local=127.0.0.3:41355 <http://127.0.0.3:41355> remote=127.0.0.1:18070 > > <http://127.0.0.1:18070> FD 40 flags=1 > > 2017/11/27 15:54:20.627| 11,2| http.cc(2230) sendRequest: HTTP Server > > REQUEST: > > --------- > > GET http://HOST:12345/ HTTP/1.1 > > User-Agent: curl/7.51.0 > > Accept: */* > > Host: HOST:12345 > > Cache-Control: max-age=259200 > > Connection: keep-alive > > > > > > ---------- > > > > [SKIPPED 40 seconds again until parent closes TCP connection with > FIN,ACK] > > > > 2017/11/27 15:55:00.728| ctx: enter level 0: 'http://HOST:12345/' > > 2017/11/27 15:55:00.728| 11,2| http.cc(719) processReplyHeader: HTTP > > Server local=127.0.0.3:41355 <http://127.0.0.3:41355> > > remote=127.0.0.1:18070 <http://127.0.0.1:18070> FD 40 flags=1 > > 2017/11/27 15:55:00.728| 11,2| http.cc(720) processReplyHeader: HTTP > > Server REPLY: > > --------- > > HTTP/1.0 502 Bad Gateway > > Cache-Control: no-cache > > Connection: close > > Content-Type: text/html > > > > <html><body><h1>502 Bad Gateway</h1> > > The server returned an invalid or incomplete response. > > </body></html> > > > > ---------- > > 2017/11/27 15:55:00.728| ctx: exit level 0 > > 2017/11/27 15:55:00.728| 20,2| store.cc(996) checkCachable: > > StoreEntry::checkCachable: NO: not cachable > > 2017/11/27 15:55:00.728| 20,2| store.cc(996) checkCachable: > > StoreEntry::checkCachable: NO: not cachable > > 2017/11/27 15:55:00.728| 88,2| client_side_reply.cc(2073) > > processReplyAccessResult: The reply for GET http://HOST:12345/ is > > ALLOWED, because it matched (access_log stdio:/var/log/squid/access.log > > line) > > 2017/11/27 15:55:00.728| 11,2| client_side.cc(1409) sendStartOfMessage: > > HTTP Client local=127.0.0.1:3128 <http://127.0.0.1:3128> > > remote=127.0.0.1:53798 <http://127.0.0.1:53798> FD 45 flags=1 > > 2017/11/27 15:55:00.728| 11,2| client_side.cc(1410) sendStartOfMessage: > > HTTP Client REPLY: > > --------- > > HTTP/1.1 502 Bad Gateway > > Date: Mon, 27 Nov 2017 23:54:20 GMT > > Cache-Control: no-cache > > Content-Type: text/html > > X-Cache: MISS from ip-172-23-18-130 > > X-Cache-Lookup: MISS from ip-172-23-18-130:3128 > > Transfer-Encoding: chunked > > Connection: keep-alive > > > > > > ---------- > -- With best regards, Ivan Larionov.
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