[BUG] global.tune.maxaccept must be limited even in mono-process mode

On overloaded systems, it sometimes happens that hundreds or thousands
of incoming connections are queued in the system's backlog, and all get
dequeued at once. The problem is that when haproxy processes them and
does not apply any limit, this can take some time and the internal date
does not progress, resulting in wrong timer measures for all sessions.

The most common effect of this is that all of these sessions report a
large request time (around several hundreds of ms) which is in fact
caused by the time spent accepting other connections. This might happen
on shared systems when the machine swaps.

For this reason, we finally apply a reasonable limit even in mono-process
mode. Accepting 100 connections at once is fast enough for extreme cases
and will not cause that much of a trouble when the system is saturated.

diff --git a/doc/configuration.txt b/doc/configuration.txt
index eb34927118ec13ab286a7842d7f2f9e219745460..18ceefdf935abda6aff990f42337ed5dc8f396d2 100644 (file)
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -251,10 +251,10 @@ tune.maxaccept <number>
   Sets the maximum number of consecutive accepts that a process may perform on
   a single wake up. High values give higher priority to high connection rates,
   while lower values give higher priority to already established connections.
-  This value is unlimited by default in single process mode. However, in
+  This value is limited to 100 by default in single process mode. However, in
   multi-process mode (nbproc > 1), it defaults to 8 so that when one process
   wakes up, it does not take all incoming connections for itself and leaves a
-  part of them to other processes. Setting this value to zero or less disables
+  part of them to other processes. Setting this value to -1 completely disables
   the limitation. It should normally not be needed to tweak this value.
 
 tune.maxpollevents <number>

diff --git a/src/haproxy.c b/src/haproxy.c
index cc6864ea4947e48d62cc6ca1baa79f972a9f11b4..d5d61251b72defbada2af015f52b27bfff32025e 100644 (file)
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -585,11 +585,11 @@ void init(int argc, char **argv)
        if (global.tune.maxpollevents <= 0)
                global.tune.maxpollevents = MAX_POLL_EVENTS;
 
-       if (global.tune.maxaccept <= 0) {
+       if (global.tune.maxaccept == 0) {
                if (global.nbproc > 1)
                        global.tune.maxaccept = 8;  /* leave some conns to other processes */
                else
-                       global.tune.maxaccept = -1; /* accept all incoming conns */
+                       global.tune.maxaccept = 100; /* accept many incoming conns at once */
        }
 
        if (arg_mode & (MODE_DEBUG | MODE_FOREGROUND)) {