[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.
(cherry picked from commit f49d1df25cf794b8801d919fda20266d90981c78)

diff --git a/doc/configuration.txt b/doc/configuration.txt
index 52ef12c8a4fb03d7f5d421561f038c04ebf423f8..72fc3878e54236fbaafdd9a174674c855c2bfc25 100644 (file)
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -229,10 +229,10 @@ 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 39b8918ed618188d70b799fa57f7d3da08fcbd84..b53608c80eeb6a22ee96b92acb979e298cf06e09 100644 (file)
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -562,11 +562,11 @@ 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)) {