Create a GUC parameter max_files_per_process that is a configurable

upper limit on what we will believe from sysconf(_SC_OPEN_MAX).  The
default value is 1000, so that under ordinary conditions it won't
affect the behavior.  But on platforms where the kernel promises far
more than it can deliver, this can be used to prevent running out of
file descriptors.  See numerous past discussions, eg, pgsql-hackers
around 23-Dec-2000.

1 files changed, 38 insertions, 13 deletions

diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index a696f1fa1fb..c2db3c8dea8 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/file/fd.c,v 1.83 2001/08/04 19:42:34 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/file/fd.c,v 1.84 2001/09/30 18:57:45 tgl Exp $
  *
  * NOTES:
  *
@@ -69,7 +69,7 @@
  *
  * (Even though most dynamic loaders now use dlopen(3) or the
  * equivalent, the OS must still open several files to perform the
- * dynamic loading.  Keep this here.)
+ * dynamic loading.  And stdin/stdout/stderr count too.  Keep this here.)
  */
 #ifndef RESERVE_FOR_LD
 #define RESERVE_FOR_LD	10
@@ -87,6 +87,14 @@
 #define FD_MINFREE 10
 #endif
 
+/*
+ * A number of platforms return values for sysconf(_SC_OPEN_MAX) that are
+ * far beyond what they can really support.  This GUC parameter limits what
+ * we will believe.
+ */
+int max_files_per_process = 1000;
+
+
 /* Debugging.... */
 
 #ifdef FDDEBUG
@@ -281,29 +289,46 @@ pg_nofile(void)
 {
 	static long no_files = 0;
 
+	/* need do this calculation only once */
 	if (no_files == 0)
 	{
-		/* need do this calculation only once */
-#ifndef HAVE_SYSCONF
-		no_files = (long) NOFILE;
-#else
+		/*
+		 * Ask the system what its files-per-process limit is.
+		 */
+#ifdef HAVE_SYSCONF
 		no_files = sysconf(_SC_OPEN_MAX);
-		if (no_files == -1)
+		if (no_files <= 0)
 		{
-/* tweak for Hurd, which does not support NOFILE */
 #ifdef NOFILE
-			elog(DEBUG, "pg_nofile: Unable to get _SC_OPEN_MAX using sysconf(); using %d", NOFILE);
 			no_files = (long) NOFILE;
 #else
-			elog(FATAL, "pg_nofile: Unable to get _SC_OPEN_MAX using sysconf() and NOFILE is undefined");
+			no_files = (long) max_files_per_process;
 #endif
+			elog(DEBUG, "pg_nofile: sysconf(_SC_OPEN_MAX) failed; using %ld",
+				 no_files);
 		}
+#else /* !HAVE_SYSCONF */
+#ifdef NOFILE
+		no_files = (long) NOFILE;
+#else
+		no_files = (long) max_files_per_process;
 #endif
+#endif /* HAVE_SYSCONF */
+
+		/*
+		 * Some platforms return hopelessly optimistic values.  Apply a
+		 * configurable upper limit.
+		 */
+		if (no_files > (long) max_files_per_process)
+			no_files = (long) max_files_per_process;
 
+		/*
+		 * Make sure we have enough to get by after reserving some for LD.
+		 */
 		if ((no_files - RESERVE_FOR_LD) < FD_MINFREE)
-			elog(FATAL, "pg_nofile: insufficient File Descriptors in postmaster to start backend (%ld).\n"
-				 "                   O/S allows %ld, Postmaster reserves %d, We need %d (MIN) after that.",
-				 no_files - RESERVE_FOR_LD, no_files, RESERVE_FOR_LD, FD_MINFREE);
+			elog(FATAL, "pg_nofile: insufficient file descriptors available to start backend.\n"
+				 "\tSystem allows %ld, we need at least %d.",
+				 no_files, RESERVE_FOR_LD + FD_MINFREE);
 
 		no_files -= RESERVE_FOR_LD;
 	}