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There have been some reported cases where races between threads in epoll
were causing wrong reports of close or error events. Since the epoll_event
data is 64 bits, we can store the FD's generation counter in the upper
bits to verify if we're speaking about the same instance of the FD as the
current one or a stale one. If the generation number does not match, then
we classify these into 3 conditions and increment the relevant COUNT_IF()
counters (stale report for closed FD, stale report of harmless event on
reopened FD, stale report of HUP/ERR on reopened FD). Tests have shown that
with heavy concurrency, a very small maxconn (typically 1 per thread),
http-reuse always and a server closing connections first but randomly
(httpterm with /C=2r), such events can happen at a pace of a few per second
for the closed FDs, and a few per minute for the other ones, so there's value
in leaving this accessible for troubleshooting. E.g after a few minutes:
Count Type Location function(): "condition" [comment]
5541 CNT ev_epoll.c:296 _do_poll(): "1" [epoll report of event on a just closed fd (harmless)]
10 CNT ev_epoll.c:294 _do_poll(): "1" [epoll report of event on a closed recycled fd (rare)]
42 CNT ev_epoll.c:289 _do_poll(): "1" [epoll report of HUP on a stale fd reopened on the same thread (suspicious)]
212 CNT ev_epoll.c:279 _do_poll(): "1" [epoll report of HUP/ERR on a stale fd reopened on another thread (harmless)]
1 CNT mux_h1.c:3911 h1_send(): "b_data(&h1c->obuf)" [connection error (send) with pending output data]
This one with the following setup, whicih abuses threads contention by
starting 64 threads on two cores:
- config:
global
nbthread 64
stats socket /tmp/sock1 level admin
stats timeout 1h
defaults
timeout client 5s
timeout server 5s
timeout connect 5s
mode http
listen p2
bind :8002
http-reuse always
server s1 127.0.0.1:8000 maxconn 4
- haproxy forcefully started on 2C4T:
$ taskset -c 0,1,4,5 ./haproxy -db -f epoll-dbg.cfg
- httpterm on port 8000, cpus 2,3,6,7 (2C4T)
- h1load with responses larger than a single buffer, and randomly
closing/keeping alive:
$ taskset -c 2,3,6,7 h1load -e -t 4 -c 256 -r 1 0:8002/?s=19k/C=2r
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HAProxy
HAProxy is a free, very fast and reliable reverse-proxy offering high availability, load balancing, and proxying for TCP and HTTP-based applications.
Installation
The INSTALL file describes how to build HAProxy. A list of packages is also available on the wiki.
Getting help
The discourse and the mailing-list are available for questions or configuration assistance. You can also use the slack or IRC channel. Please don't use the issue tracker for these.
The issue tracker is only for bug reports or feature requests.
Documentation
The HAProxy documentation has been split into a number of different files for ease of use. It is available in text format as well as HTML. The wiki is also meant to replace the old architecture guide.
Please refer to the following files depending on what you're looking for:
- INSTALL for instructions on how to build and install HAProxy
- BRANCHES to understand the project's life cycle and what version to use
- LICENSE for the project's license
- CONTRIBUTING for the process to follow to submit contributions
The more detailed documentation is located into the doc/ directory:
- doc/intro.txt for a quick introduction on HAProxy
- doc/configuration.txt for the configuration's reference manual
- doc/lua.txt for the Lua's reference manual
- doc/SPOE.txt for how to use the SPOE engine
- doc/network-namespaces.txt for how to use network namespaces under Linux
- doc/management.txt for the management guide
- doc/regression-testing.txt for how to use the regression testing suite
- doc/peers.txt for the peers protocol reference
- doc/coding-style.txt for how to adopt HAProxy's coding style
- doc/internals for developer-specific documentation (not all up to date)
License
HAProxy is licensed under GPL 2 or any later version, the headers under LGPL 2.1. See the LICENSE file for a more detailed explanation.