initdb: Add --no-sync-data-files.

This new option instructs initdb to skip synchronizing any files
in database directories, the database directories themselves, and
the tablespace directories, i.e., everything in the base/
subdirectory and any other tablespace directories.  Other files,
such as those in pg_wal/ and pg_xact/, will still be synchronized
unless --no-sync is also specified.  --no-sync-data-files is
primarily intended for internal use by tools that separately ensure
the skipped files are synchronized to disk.  A follow-up commit
will use this to help optimize pg_upgrade's file transfer step.

The --sync-method=fsync implementation of this option makes use of
a new exclude_dir parameter for walkdir().  When not NULL,
exclude_dir specifies a directory to skip processing.  The
--sync-method=syncfs implementation of this option just skips
synchronizing the non-default tablespace directories.  This means
that initdb will still synchronize some or all of the database
files, but there's not much we can do about that.

Discussion: https://postgr.es/m/Zyvop-LxLXBLrZil%40nathan

2 files changed, 9 insertions, 2 deletions

diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 21a0fe3ecd9..22b7d31b165 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -168,6 +168,7 @@ static bool data_checksums = true;
 static char *xlog_dir = NULL;
 static int	wal_segment_size_mb = (DEFAULT_XLOG_SEG_SIZE) / (1024 * 1024);
 static DataDirSyncMethod sync_method = DATA_DIR_SYNC_METHOD_FSYNC;
+static bool sync_data_files = true;
 
 
 /* internal vars */
@@ -2566,6 +2567,7 @@ usage(const char *progname)
 	printf(_("  -L DIRECTORY              where to find the input files\n"));
 	printf(_("  -n, --no-clean            do not clean up after errors\n"));
 	printf(_("  -N, --no-sync             do not wait for changes to be written safely to disk\n"));
+	printf(_("      --no-sync-data-files  do not sync files within database directories\n"));
 	printf(_("      --no-instructions     do not print instructions for next steps\n"));
 	printf(_("  -s, --show                show internal settings, then exit\n"));
 	printf(_("      --sync-method=METHOD  set method for syncing files to disk\n"));
@@ -3208,6 +3210,7 @@ main(int argc, char *argv[])
 		{"icu-rules", required_argument, NULL, 18},
 		{"sync-method", required_argument, NULL, 19},
 		{"no-data-checksums", no_argument, NULL, 20},
+		{"no-sync-data-files", no_argument, NULL, 21},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -3402,6 +3405,9 @@ main(int argc, char *argv[])
 			case 20:
 				data_checksums = false;
 				break;
+			case 21:
+				sync_data_files = false;
+				break;
 			default:
 				/* getopt_long already emitted a complaint */
 				pg_log_error_hint("Try \"%s --help\" for more information.", progname);
@@ -3453,7 +3459,7 @@ main(int argc, char *argv[])
 
 		fputs(_("syncing data to disk ... "), stdout);
 		fflush(stdout);
-		sync_pgdata(pg_data, PG_VERSION_NUM, sync_method);
+		sync_pgdata(pg_data, PG_VERSION_NUM, sync_method, sync_data_files);
 		check_ok();
 		return 0;
 	}
@@ -3516,7 +3522,7 @@ main(int argc, char *argv[])
 	{
 		fputs(_("syncing data to disk ... "), stdout);
 		fflush(stdout);
-		sync_pgdata(pg_data, PG_VERSION_NUM, sync_method);
+		sync_pgdata(pg_data, PG_VERSION_NUM, sync_method, sync_data_files);
 		check_ok();
 	}
 	else
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index 01cc4a1602b..15dd10ce40a 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -76,6 +76,7 @@ command_like(
 	'checksums are enabled in control file');
 
 command_ok([ 'initdb', '--sync-only', $datadir ], 'sync only');
+command_ok([ 'initdb', '--sync-only', '--no-sync-data-files', $datadir ], '--no-sync-data-files');
 command_fails([ 'initdb', $datadir ], 'existing data directory');
 
 if ($supports_syncfs)