Clean up initdb's code for selecting max_connections and shared_buffers

a little bit, and set the minimum buffers-per-connection ratio to 10 not
5.  I folded the two test routines into one to counteract the illusion
that the tests can be twiddled independently, and added some documentation
pointing out the necessary connection between the sets of values tested.
Fixes strange choices of parameters that I noticed CVS tip making on
Darwin with Apple's undersized default SHMMAX.

src/bin/initdb/initdb.c

@@ -42,7 +42,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  * Portions taken from FreeBSD.
  *
- * $PostgreSQL: pgsql/src/bin/initdb/initdb.c,v 1.102 2005/12/27 23:54:01 adunstan Exp $
+ * $PostgreSQL: pgsql/src/bin/initdb/initdb.c,v 1.103 2005/12/31 23:50:59 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -169,8 +169,7 @@ static void set_input(char **dest, char *filename);
 static void check_input(char *path);
 static void set_short_version(char *short_version, char *extrapath);
 static void set_null_conf(void);
-static void test_connections(void);
-static void test_buffers(void);
+static void test_config_settings(void);
 static void setup_config(void);
 static void bootstrap_template1(char *short_version);
 static void setup_auth(void);
@@ -1059,7 +1058,8 @@ set_short_version(char *short_version, char *extrapath)
 }
 
 /*
- * set up an empty config file so we can check buffers and connections
+ * set up an empty config file so we can check config settings by launching
+ * a test backend
  */
 static void
 set_null_conf(void)
@@ -1085,93 +1085,98 @@ set_null_conf(void)
 }
 
 /*
- * max_fsm_pages setting used in both the shared_buffers and max_connections
- * tests. 
- */
-
-#define TEST_FSM(x) ( (x) > 1000 ? 50 * (x) : 20000 )
-
-/*
- * check how many connections we can sustain
+ * Determine platform-specific config settings
+ *
+ * Use reasonable values if kernel will let us, else scale back.  Probe
+ * for max_connections first since it is subject to more constraints than
+ * shared_buffers.
  */
 static void
-test_connections(void)
+test_config_settings(void)
 {
+	/*
+	 * These macros define the minimum shared_buffers we want for a given
+	 * max_connections value, and the max_fsm_pages setting to be used for
+	 * a given shared_buffers value.  The arrays show the settings to try.
+	 *
+	 * Make sure the trial_bufs[] list includes the MIN_BUFS_FOR_CONNS()
+	 * value for each trial_conns[] entry, else we may end up setting
+	 * shared_buffers lower than it could be.
+	 */
+#define MIN_BUFS_FOR_CONNS(nconns)  ((nconns) * 10)
+#define FSM_FOR_BUFS(nbuffers)  ((nbuffers) > 1000 ? 50 * (nbuffers) : 20000)
+
+	static const int trial_conns[] = {
+		100, 50, 40, 30, 20, 10
+	};
+	static const int trial_bufs[] = {
+		4000, 3500, 3000, 2500, 2000, 1500,
+		1000, 900, 800, 700, 600, 500,
+		400, 300, 200, 100, 50
+	};
+
 	char		cmd[MAXPGPATH];
-	static const int conns[] = {100, 50, 40, 30, 20, 10};
-	static const int len = sizeof(conns) / sizeof(int);
+	const int connslen = sizeof(trial_conns) / sizeof(int);
+	const int bufslen = sizeof(trial_bufs) / sizeof(int);
 	int			i,
-				status;
+				status,
+				test_conns,
+				test_buffs,
+				test_max_fsm;
 
 	printf(_("selecting default max_connections ... "));
 	fflush(stdout);
 
-	for (i = 0; i < len; i++)
+	for (i = 0; i < connslen; i++)
 	{
-		int test_buffs = conns[i] * 5;
-		int test_max_fsm =  TEST_FSM(test_buffs);
+		test_conns = trial_conns[i];
+		test_buffs = MIN_BUFS_FOR_CONNS(test_conns);
+		test_max_fsm = FSM_FOR_BUFS(test_buffs);
 
 		snprintf(cmd, sizeof(cmd),
 				 "%s\"%s\" -boot -x0 %s "
+				 "-c max_connections=%d "
+				 "-c shared_buffers=%d "
 				 "-c max_fsm_pages=%d "
-				 "-c shared_buffers=%d -c max_connections=%d template1 "
-				 "< \"%s\" > \"%s\" 2>&1%s",
+				 "template1 < \"%s\" > \"%s\" 2>&1%s",
 				 SYSTEMQUOTE, backend_exec, boot_options,
-				 test_max_fsm,
-				 test_buffs, conns[i],
+				 test_conns, test_buffs, test_max_fsm,
 				 DEVNULL, DEVNULL, SYSTEMQUOTE);
 		status = system(cmd);
 		if (status == 0)
 			break;
 	}
-	if (i >= len)
-		i = len - 1;
-	n_connections = conns[i];
+	if (i >= connslen)
+		i = connslen - 1;
+	n_connections = trial_conns[i];
 
 	printf("%d\n", n_connections);
-}
-
-/*
- * check how many buffers we can run with
- */
-static void
-test_buffers(void)
-{
-	char		cmd[MAXPGPATH];
-	static const int bufs[] = {
-	  4000, 3500, 3000, 2500, 2000, 1500,
-	  1000, 900, 800, 700, 600, 500,
-	  400, 300, 200, 100, 50
-	};
-	static const int len = sizeof(bufs) / sizeof(int);
-	int			i,
-				status,
-	            test_max_fsm_pages;
 
 	printf(_("selecting default shared_buffers/max_fsm_pages ... "));
 	fflush(stdout);
 
-	for (i = 0; i < len; i++)
+	for (i = 0; i < bufslen; i++)
 	{
-		test_max_fsm_pages = TEST_FSM(bufs[i]);
+		test_buffs = trial_bufs[i];
+		test_max_fsm = FSM_FOR_BUFS(test_buffs);
 
 		snprintf(cmd, sizeof(cmd),
 				 "%s\"%s\" -boot -x0 %s "
+				 "-c max_connections=%d "
+				 "-c shared_buffers=%d "
 				 "-c max_fsm_pages=%d "
-				 "-c shared_buffers=%d -c max_connections=%d template1 "
-				 "< \"%s\" > \"%s\" 2>&1%s",
+				 "template1 < \"%s\" > \"%s\" 2>&1%s",
 				 SYSTEMQUOTE, backend_exec, boot_options,
-				 test_max_fsm_pages,
-				 bufs[i], n_connections,
+				 n_connections, test_buffs, test_max_fsm,
 				 DEVNULL, DEVNULL, SYSTEMQUOTE);
 		status = system(cmd);
 		if (status == 0)
 			break;
 	}
-	if (i >= len)
-		i = len - 1;
-	n_buffers = bufs[i];
-	n_fsm_pages = test_max_fsm_pages;
+	if (i >= bufslen)
+		i = bufslen - 1;
+	n_buffers = trial_bufs[i];
+	n_fsm_pages = FSM_FOR_BUFS(n_buffers);
 
 	printf("%d/%d\n", n_buffers, n_fsm_pages);
 }
@@ -2745,18 +2750,9 @@ main(int argc, char *argv[])
 	/* Top level PG_VERSION is checked by bootstrapper, so make it first */
 	set_short_version(short_version, NULL);
 
-	/*
-	 * Determine platform-specific config settings
-	 *
-	 * Use reasonable values if kernel will let us, else scale back.  Probe
-	 * for max_connections first since it is subject to more constraints than
-	 * shared_buffers.
-	 */
-
+	/* Select suitable configuration settings */
 	set_null_conf();
-
-	test_connections();
-	test_buffers();
+	test_config_settings();
 
 	/* Now create all the text config files */
 	setup_config();