Add --clobber-cache option to initdb, for CCA testing.

Commit 4656e3d66 replaced the "#define CLOBBER_CACHE_ALWAYS"
testing mechanism with a GUC, which has been a great help for
doing cache-clobber testing in more efficient ways; but there
is a gap in the implementation.  The only way to do cache-clobber
testing during an initdb run is to use the old method with #define,
because one can't set the GUC from outside.  Improve this by
adding a switch to initdb for the purpose.

(Perhaps someday we should let initdb pass through arbitrary
"-c NAME=VALUE" switches.  Quoting difficulties dissuaded me
from attempting that right now, though.)

Back-patch to v14 where 4656e3d66 came in.

Discussion: https://postgr.es/m/1582507.1624227029@sss.pgh.pa.us

doc/src/sgml/ref/initdb.sgml

@@ -388,6 +388,17 @@ PostgreSQL documentation
     Other, less commonly used, options are also available:
 
     <variablelist>
+     <varlistentry>
+      <term><option>--clobber-cache</option></term>
+      <listitem>
+       <para>
+        Run the bootstrap backend with the
+        <literal>debug_invalidate_system_caches_always=1</literal> option.
+        This takes a very long time and is only of use for deep debugging.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-d</option></term>
       <term><option>--debug</option></term>

src/bin/initdb/initdb.c

@@ -202,6 +202,9 @@ static bool authwarning = false;
 static const char *boot_options = "-F";
 static const char *backend_options = "--single -F -O -j -c search_path=pg_catalog -c exit_on_error=true";
 
+/* Additional switches to pass to backend (either boot or standalone) */
+static char *extra_options = "";
+
 static const char *const subdirs[] = {
 	"global",
 	"pg_wal/archive_status",
@@ -962,12 +965,12 @@ test_config_settings(void)
 		test_buffs = MIN_BUFS_FOR_CONNS(test_conns);
 
 		snprintf(cmd, sizeof(cmd),
-				 "\"%s\" --boot -x0 %s "
+				 "\"%s\" --boot -x0 %s %s "
 				 "-c max_connections=%d "
 				 "-c shared_buffers=%d "
 				 "-c dynamic_shared_memory_type=%s "
 				 "< \"%s\" > \"%s\" 2>&1",
-				 backend_exec, boot_options,
+				 backend_exec, boot_options, extra_options,
 				 test_conns, test_buffs,
 				 dynamic_shared_memory_type,
 				 DEVNULL, DEVNULL);
@@ -998,12 +1001,12 @@ test_config_settings(void)
 		}
 
 		snprintf(cmd, sizeof(cmd),
-				 "\"%s\" --boot -x0 %s "
+				 "\"%s\" --boot -x0 %s %s "
 				 "-c max_connections=%d "
 				 "-c shared_buffers=%d "
 				 "-c dynamic_shared_memory_type=%s "
 				 "< \"%s\" > \"%s\" 2>&1",
-				 backend_exec, boot_options,
+				 backend_exec, boot_options, extra_options,
 				 n_connections, test_buffs,
 				 dynamic_shared_memory_type,
 				 DEVNULL, DEVNULL);
@@ -1403,11 +1406,11 @@ bootstrap_template1(void)
 	unsetenv("PGCLIENTENCODING");
 
 	snprintf(cmd, sizeof(cmd),
-			 "\"%s\" --boot -x1 -X %u %s %s %s",
+			 "\"%s\" --boot -x1 -X %u %s %s %s %s",
 			 backend_exec,
 			 wal_segment_size_mb * (1024 * 1024),
 			 data_checksums ? "-k" : "",
-			 boot_options,
+			 boot_options, extra_options,
 			 debug ? "-d 5" : "");
 
 
@@ -2263,6 +2266,7 @@ usage(const char *progname)
 	printf(_("  -X, --waldir=WALDIR       location for the write-ahead log directory\n"));
 	printf(_("      --wal-segsize=SIZE    size of WAL segments, in megabytes\n"));
 	printf(_("\nLess commonly used options:\n"));
+	printf(_("      --clobber-cache       use cache-clobbering debug option\n"));
 	printf(_("  -d, --debug               generate lots of debugging output\n"));
 	printf(_("  -L DIRECTORY              where to find the input files\n"));
 	printf(_("  -n, --no-clean            do not clean up after errors\n"));
@@ -2863,8 +2867,8 @@ initialize_data_directory(void)
 	fflush(stdout);
 
 	snprintf(cmd, sizeof(cmd),
-			 "\"%s\" %s template1 >%s",
+			 "\"%s\" %s %s template1 >%s",
-			 backend_exec, backend_options,
+			 backend_exec, backend_options, extra_options,
 			 DEVNULL);
 
 	PG_CMD_OPEN;
@@ -2943,6 +2947,7 @@ main(int argc, char *argv[])
 		{"wal-segsize", required_argument, NULL, 12},
 		{"data-checksums", no_argument, NULL, 'k'},
 		{"allow-group-access", no_argument, NULL, 'g'},
+		{"clobber-cache", no_argument, NULL, 14},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -3084,6 +3089,11 @@ main(int argc, char *argv[])
 			case 'g':
 				SetDataDirectoryCreatePerm(PG_DIR_MODE_GROUP);
 				break;
+			case 14:
+				extra_options = psprintf("%s %s",
+										 extra_options,
+										 "-c debug_invalidate_system_caches_always=1");
+				break;
 			default:
 				/* getopt_long already emitted a complaint */
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"),