http://patchlog.com/linux/qmail-big-concurrency/

--- select.h2	1998-06-15 13:53:16.000000000 +0300
+++ select.h2	2009-09-05 13:14:36.000000000 +0300
@@ -1,6 +1,12 @@
 #ifndef SELECT_H
 #define SELECT_H
 
+#include <features.h>
+#if (__GLIBC__ > 2) || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 2)
+# include <bits/types.h>
+# undef __FD_SETSIZE
+# define __FD_SETSIZE 131077
+#endif 
 #include <sys/types.h>
 #include <sys/time.h>
 #include <sys/select.h>
--- spawn.c	2008-11-07 23:15:20.000000000 +0200
+++ spawn.c	2009-09-05 15:51:29.000000000 +0300
@@ -1,4 +1,4 @@
-#include <sys/types.h>
+#include "select.h"
 #include <sys/stat.h>
 #include "sig.h"
 #include "wait.h"
@@ -7,7 +7,6 @@
 #include "str.h"
 #include "alloc.h"
 #include "stralloc.h"
-#include "select.h"
 #include "exit.h"
 #include "coe.h"
 #include "open.h"
--- conf-spawn	2009-09-04 23:52:03.000000000 +0300
+++ conf-spawn	2009-09-05 16:15:41.000000000 +0300
@@ -1 +1 @@
-500
+4000