Instead of believing SOMAXCONN from the system header files (which is

a lie on many Unixen), invoke listen() with MIN(MaxBackends*2, 10000).
The clamp value 10000 is configurable in config.h.in, if that proves
to be necessary --- hopefully it won't.

2 files changed, 30 insertions, 6 deletions

diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c
index 844c9d9cbd..3293ea47a7 100644
--- a/src/backend/libpq/pqcomm.c
+++ b/src/backend/libpq/pqcomm.c
@@ -80,11 +80,6 @@
 #include "miscadmin.h"
 
 
-#ifndef SOMAXCONN
-#define SOMAXCONN 5				/* from Linux listen(2) man page */
-#endif
-
-
 static void pq_close(void);
 
 
@@ -185,6 +180,7 @@ StreamServerPort(int family, char *hostName, unsigned short portNumber,
 	SockAddr	saddr;
 	int			fd,
 				err;
+	int			maxconn;
 	size_t		len = 0;
 	int			one = 1;
 
@@ -350,7 +346,25 @@ StreamServerPort(int family, char *hostName, unsigned short portNumber,
 	}
 #endif	 /* HAVE_UNIX_SOCKETS */
 
-	listen(fd, SOMAXCONN);
+	/*
+	 * Select appropriate accept-queue length limit.  PG_SOMAXCONN is
+	 * only intended to provide a clamp on the request on platforms where
+	 * an overly large request provokes a kernel error (are there any?).
+	 */
+	maxconn = MaxBackends * 2;
+	if (maxconn > PG_SOMAXCONN)
+		maxconn = PG_SOMAXCONN;
+
+	err = listen(fd, maxconn);
+	if (err < 0)
+	{
+		snprintf(PQerrormsg, PQERRORMSG_LENGTH,
+				 "FATAL: StreamServerPort: listen() failed: %s\n",
+				 strerror(errno));
+		fputs(PQerrormsg, stderr);
+		pqdebug("%s", PQerrormsg);
+		return STATUS_ERROR;
+	}
 
 	*fdP = fd;
 
diff --git a/src/include/config.h.in b/src/include/config.h.in
index ed0b5832e1..934abd537e 100644
--- a/src/include/config.h.in
+++ b/src/include/config.h.in
@@ -233,6 +233,16 @@
 #define DEFAULT_MAX_EXPR_DEPTH	10000
 
 /*
+ * PG_SOMAXCONN: maximum accept-queue length limit passed to listen(2).
+ * You'd think we should use SOMAXCONN from <sys/socket.h>, but on many
+ * systems that symbol is much smaller than the kernel's actual limit.
+ * In any case, this symbol need be twiddled only if you have a kernel
+ * that refuses large limit values, rather than silently reducing the
+ * value to what it can handle (which is what most if not all Unixen do).
+ */
+#define PG_SOMAXCONN	10000
+
+/*
  * You can try changing this if you have a machine with bytes of another
  * size, but no guarantee...
  */