Add support for syncfs() in frontend support functions.

This commit adds support for using syncfs() in fsync_pgdata() and
fsync_dir_recurse() (which have been renamed to sync_pgdata() and
sync_dir_recurse()).  Like recovery_init_sync_method,
sync_pgdata() calls syncfs() for the data directory, each
tablespace, and pg_wal (if it is a symlink).  For now, all of the
frontend utilities that use these support functions are hard-coded
to use fsync(), but a follow-up commit will allow specifying
syncfs().

Co-authored-by: Justin Pryzby
Reviewed-by: Michael Paquier
Discussion: https://postgr.es/m/20210930004340.GM831%40telsasoft.com

src/bin/initdb/initdb.c

@@ -165,6 +165,7 @@ static bool show_setting = false;
 static bool data_checksums = false;
 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;
 
 
 /* internal vars */
@@ -3322,7 +3323,7 @@ main(int argc, char *argv[])
 
 	atexit(cleanup_directories_atexit);
 
-	/* If we only need to fsync, just do it and exit */
+	/* If we only need to sync, just do it and exit */
 	if (sync_only)
 	{
 		setup_pgdata();
@@ -3333,7 +3334,7 @@ main(int argc, char *argv[])
 
 		fputs(_("syncing data to disk ... "), stdout);
 		fflush(stdout);
-		fsync_pgdata(pg_data, PG_VERSION_NUM);
+		sync_pgdata(pg_data, PG_VERSION_NUM, sync_method);
 		check_ok();
 		return 0;
 	}
@@ -3396,7 +3397,7 @@ main(int argc, char *argv[])
 	{
 		fputs(_("syncing data to disk ... "), stdout);
 		fflush(stdout);
-		fsync_pgdata(pg_data, PG_VERSION_NUM);
+		sync_pgdata(pg_data, PG_VERSION_NUM, sync_method);
 		check_ok();
 	}
 	else

src/bin/pg_basebackup/pg_basebackup.c

@@ -148,6 +148,7 @@ static bool verify_checksums = true;
 static bool manifest = true;
 static bool manifest_force_encode = false;
 static char *manifest_checksums = NULL;
+static DataDirSyncMethod sync_method = DATA_DIR_SYNC_METHOD_FSYNC;
 
 static bool success = false;
 static bool made_new_pgdata = false;
@@ -2199,11 +2200,11 @@ BaseBackup(char *compression_algorithm, char *compression_detail,
 		if (format == 't')
 		{
 			if (strcmp(basedir, "-") != 0)
-				(void) fsync_dir_recurse(basedir);
+				(void) sync_dir_recurse(basedir, sync_method);
 		}
 		else
 		{
-			(void) fsync_pgdata(basedir, serverVersion);
+			(void) sync_pgdata(basedir, serverVersion, sync_method);
 		}
 	}
 

src/bin/pg_checksums/pg_checksums.c

@@ -44,6 +44,7 @@ static char *only_filenode = NULL;
 static bool do_sync = true;
 static bool verbose = false;
 static bool showprogress = false;
+static DataDirSyncMethod sync_method = DATA_DIR_SYNC_METHOD_FSYNC;
 
 typedef enum
 {
@@ -623,7 +624,7 @@ main(int argc, char *argv[])
 		if (do_sync)
 		{
 			pg_log_info("syncing data directory");
-			fsync_pgdata(DataDir, PG_VERSION_NUM);
+			sync_pgdata(DataDir, PG_VERSION_NUM, sync_method);
 		}
 
 		pg_log_info("updating control file");

src/bin/pg_dump/pg_backup.h

@@ -24,6 +24,7 @@
 #define PG_BACKUP_H
 
 #include "common/compression.h"
+#include "common/file_utils.h"
 #include "fe_utils/simple_list.h"
 #include "libpq-fe.h"
 
@@ -307,7 +308,8 @@ extern Archive *OpenArchive(const char *FileSpec, const ArchiveFormat fmt);
 extern Archive *CreateArchive(const char *FileSpec, const ArchiveFormat fmt,
 							  const pg_compress_specification compression_spec,
 							  bool dosync, ArchiveMode mode,
-							  SetupWorkerPtrType setupDumpWorker);
+							  SetupWorkerPtrType setupDumpWorker,
+							  DataDirSyncMethod sync_method);
 
 /* The --list option */
 extern void PrintTOCSummary(Archive *AHX);

src/bin/pg_dump/pg_backup_archiver.c

@@ -66,7 +66,8 @@ typedef struct _parallelReadyList
 static ArchiveHandle *_allocAH(const char *FileSpec, const ArchiveFormat fmt,
 							   const pg_compress_specification compression_spec,
 							   bool dosync, ArchiveMode mode,
-							   SetupWorkerPtrType setupWorkerPtr);
+							   SetupWorkerPtrType setupWorkerPtr,
+							   DataDirSyncMethod sync_method);
 static void _getObjectDescription(PQExpBuffer buf, const TocEntry *te);
 static void _printTocEntry(ArchiveHandle *AH, TocEntry *te, bool isData);
 static char *sanitize_line(const char *str, bool want_hyphen);
@@ -238,11 +239,12 @@ Archive *
 CreateArchive(const char *FileSpec, const ArchiveFormat fmt,
 			  const pg_compress_specification compression_spec,
 			  bool dosync, ArchiveMode mode,
-			  SetupWorkerPtrType setupDumpWorker)
+			  SetupWorkerPtrType setupDumpWorker,
+			  DataDirSyncMethod sync_method)
 
 {
 	ArchiveHandle *AH = _allocAH(FileSpec, fmt, compression_spec,
-								 dosync, mode, setupDumpWorker);
+								 dosync, mode, setupDumpWorker, sync_method);
 
 	return (Archive *) AH;
 }
@@ -257,7 +259,8 @@ OpenArchive(const char *FileSpec, const ArchiveFormat fmt)
 
 	compression_spec.algorithm = PG_COMPRESSION_NONE;
 	AH = _allocAH(FileSpec, fmt, compression_spec, true,
-				  archModeRead, setupRestoreWorker);
+				  archModeRead, setupRestoreWorker,
+				  DATA_DIR_SYNC_METHOD_FSYNC);
 
 	return (Archive *) AH;
 }
@@ -2233,7 +2236,7 @@ static ArchiveHandle *
 _allocAH(const char *FileSpec, const ArchiveFormat fmt,
 		 const pg_compress_specification compression_spec,
 		 bool dosync, ArchiveMode mode,
-		 SetupWorkerPtrType setupWorkerPtr)
+		 SetupWorkerPtrType setupWorkerPtr, DataDirSyncMethod sync_method)
 {
 	ArchiveHandle *AH;
 	CompressFileHandle *CFH;
@@ -2287,6 +2290,7 @@ _allocAH(const char *FileSpec, const ArchiveFormat fmt,
 	AH->mode = mode;
 	AH->compression_spec = compression_spec;
 	AH->dosync = dosync;
+	AH->sync_method = sync_method;
 
 	memset(&(AH->sqlparse), 0, sizeof(AH->sqlparse));
 

src/bin/pg_dump/pg_backup_archiver.h

@@ -312,6 +312,7 @@ struct _archiveHandle
 	pg_compress_specification compression_spec; /* Requested specification for
 												 * compression */
 	bool		dosync;			/* data requested to be synced on sight */
+	DataDirSyncMethod sync_method;
 	ArchiveMode mode;			/* File mode - r or w */
 	void	   *formatData;		/* Header data specific to file format */
 

src/bin/pg_dump/pg_backup_directory.c

@@ -613,7 +613,7 @@ _CloseArchive(ArchiveHandle *AH)
 		 * individually. Just recurse once through all the files generated.
 		 */
 		if (AH->dosync)
-			fsync_dir_recurse(ctx->directory);
+			sync_dir_recurse(ctx->directory, AH->sync_method);
 	}
 	AH->FH = NULL;
 }

src/bin/pg_dump/pg_dump.c

@@ -357,6 +357,7 @@ main(int argc, char **argv)
 	char	   *compression_algorithm_str = "none";
 	char	   *error_detail = NULL;
 	bool		user_compression_defined = false;
+	DataDirSyncMethod sync_method = DATA_DIR_SYNC_METHOD_FSYNC;
 
 	static DumpOptions dopt;
 
@@ -777,7 +778,7 @@ main(int argc, char **argv)
 
 	/* Open the output file */
 	fout = CreateArchive(filename, archiveFormat, compression_spec,
-						 dosync, archiveMode, setupDumpWorker);
+						 dosync, archiveMode, setupDumpWorker, sync_method);
 
 	/* Make dump options accessible right away */
 	SetArchiveOptions(fout, &dopt, NULL);

src/bin/pg_rewind/file_ops.c

@@ -286,9 +286,9 @@ remove_target_symlink(const char *path)
  *
  * We do this once, for the whole data directory, for performance reasons.  At
  * the end of pg_rewind's run, the kernel is likely to already have flushed
- * most dirty buffers to disk.  Additionally fsync_pgdata uses a two-pass
- * approach (only initiating writeback in the first pass), which often reduces
- * the overall amount of IO noticeably.
+ * most dirty buffers to disk.  Additionally sync_pgdata uses a two-pass
+ * approach when fsync is specified (only initiating writeback in the first
+ * pass), which often reduces the overall amount of IO noticeably.
  */
 void
 sync_target_dir(void)
@@ -296,7 +296,7 @@ sync_target_dir(void)
 	if (!do_sync || dry_run)
 		return;
 
-	fsync_pgdata(datadir_target, PG_VERSION_NUM);
+	sync_pgdata(datadir_target, PG_VERSION_NUM, sync_method);
 }
 
 

src/bin/pg_rewind/pg_rewind.c

@@ -74,6 +74,7 @@ bool		showprogress = false;
 bool		dry_run = false;
 bool		do_sync = true;
 bool		restore_wal = false;
+DataDirSyncMethod sync_method = DATA_DIR_SYNC_METHOD_FSYNC;
 
 /* Target history */
 TimeLineHistoryEntry *targetHistory;

src/bin/pg_rewind/pg_rewind.h

@@ -13,6 +13,7 @@
 
 #include "access/timeline.h"
 #include "common/logging.h"
+#include "common/file_utils.h"
 #include "datapagemap.h"
 #include "libpq-fe.h"
 #include "storage/block.h"
@@ -24,6 +25,7 @@ extern bool showprogress;
 extern bool dry_run;
 extern bool do_sync;
 extern int	WalSegSz;
+extern DataDirSyncMethod sync_method;
 
 /* Target history */
 extern TimeLineHistoryEntry *targetHistory;

src/common/file_utils.c

@@ -51,19 +51,52 @@ static void walkdir(const char *path,
 					int (*action) (const char *fname, bool isdir),
 					bool process_symlinks);
 
+#ifdef HAVE_SYNCFS
+
 /*
- * Issue fsync recursively on PGDATA and all its contents.
+ * do_syncfs -- Try to syncfs a file system
  *
- * We fsync regular files and directories wherever they are, but we follow
+ * Reports errors trying to open the path.  syncfs() errors are fatal.
+ */
+static void
+do_syncfs(const char *path)
+{
+	int			fd;
+
+	fd = open(path, O_RDONLY, 0);
+
+	if (fd < 0)
+	{
+		pg_log_error("could not open file \"%s\": %m", path);
+		return;
+	}
+
+	if (syncfs(fd) < 0)
+	{
+		pg_log_error("could not synchronize file system for file \"%s\": %m", path);
+		(void) close(fd);
+		exit(EXIT_FAILURE);
+	}
+
+	(void) close(fd);
+}
+
+#endif							/* HAVE_SYNCFS */
+
+/*
+ * Synchronize PGDATA and all its contents.
+ *
+ * We sync regular files and directories wherever they are, but we follow
  * symlinks only for pg_wal (or pg_xlog) and immediately under pg_tblspc.
  * Other symlinks are presumed to point at files we're not responsible for
- * fsyncing, and might not have privileges to write at all.
+ * syncing, and might not have privileges to write at all.
  *
- * serverVersion indicates the version of the server to be fsync'd.
+ * serverVersion indicates the version of the server to be sync'd.
  */
 void
-fsync_pgdata(const char *pg_data,
-			 int serverVersion)
+sync_pgdata(const char *pg_data,
+			int serverVersion,
+			DataDirSyncMethod sync_method)
 {
 	bool		xlog_is_symlink;
 	char		pg_wal[MAXPGPATH];
@@ -89,9 +122,68 @@ fsync_pgdata(const char *pg_data,
 			xlog_is_symlink = true;
 	}
 
+	switch (sync_method)
+	{
+		case DATA_DIR_SYNC_METHOD_SYNCFS:
+			{
+#ifndef HAVE_SYNCFS
+				pg_log_error("this build does not support sync method \"%s\"",
+							 "syncfs");
+				exit(EXIT_FAILURE);
+#else
+				DIR		   *dir;
+				struct dirent *de;
+
 				/*
-	 * If possible, hint to the kernel that we're soon going to fsync the data
-	 * directory and its contents.
+				 * On Linux, we don't have to open every single file one by
+				 * one.  We can use syncfs() to sync whole filesystems.  We
+				 * only expect filesystem boundaries to exist where we
+				 * tolerate symlinks, namely pg_wal and the tablespaces, so we
+				 * call syncfs() for each of those directories.
+				 */
+
+				/* Sync the top level pgdata directory. */
+				do_syncfs(pg_data);
+
+				/* If any tablespaces are configured, sync each of those. */
+				dir = opendir(pg_tblspc);
+				if (dir == NULL)
+					pg_log_error("could not open directory \"%s\": %m",
+								 pg_tblspc);
+				else
+				{
+					while (errno = 0, (de = readdir(dir)) != NULL)
+					{
+						char		subpath[MAXPGPATH * 2];
+
+						if (strcmp(de->d_name, ".") == 0 ||
+							strcmp(de->d_name, "..") == 0)
+							continue;
+
+						snprintf(subpath, sizeof(subpath), "%s/%s",
+								 pg_tblspc, de->d_name);
+						do_syncfs(subpath);
+					}
+
+					if (errno)
+						pg_log_error("could not read directory \"%s\": %m",
+									 pg_tblspc);
+
+					(void) closedir(dir);
+				}
+
+				/* If pg_wal is a symlink, process that too. */
+				if (xlog_is_symlink)
+					do_syncfs(pg_wal);
+#endif							/* HAVE_SYNCFS */
+			}
+			break;
+
+		case DATA_DIR_SYNC_METHOD_FSYNC:
+			{
+				/*
+				 * If possible, hint to the kernel that we're soon going to
+				 * fsync the data directory and its contents.
 				 */
 #ifdef PG_FLUSH_DATA_WORKS
 				walkdir(pg_data, pre_sync_fname, false);
@@ -103,29 +195,53 @@ fsync_pgdata(const char *pg_data,
 				/*
 				 * Now we do the fsync()s in the same order.
 				 *
-	 * The main call ignores symlinks, so in addition to specially processing
-	 * pg_wal if it's a symlink, pg_tblspc has to be visited separately with
-	 * process_symlinks = true.  Note that if there are any plain directories
-	 * in pg_tblspc, they'll get fsync'd twice.  That's not an expected case
-	 * so we don't worry about optimizing it.
+				 * The main call ignores symlinks, so in addition to specially
+				 * processing pg_wal if it's a symlink, pg_tblspc has to be
+				 * visited separately with process_symlinks = true.  Note that
+				 * if there are any plain directories in pg_tblspc, they'll
+				 * get fsync'd twice. That's not an expected case so we don't
+				 * worry about optimizing it.
 				 */
 				walkdir(pg_data, fsync_fname, false);
 				if (xlog_is_symlink)
 					walkdir(pg_wal, fsync_fname, false);
 				walkdir(pg_tblspc, fsync_fname, true);
 			}
+			break;
+	}
+}
 
 /*
- * Issue fsync recursively on the given directory and all its contents.
+ * Synchronize the given directory and all its contents.
  *
- * This is a convenient wrapper on top of walkdir().
+ * This is a convenient wrapper on top of walkdir() and do_syncfs().
  */
 void
-fsync_dir_recurse(const char *dir)
+sync_dir_recurse(const char *dir, DataDirSyncMethod sync_method)
+{
+	switch (sync_method)
+	{
+		case DATA_DIR_SYNC_METHOD_SYNCFS:
+			{
+#ifndef HAVE_SYNCFS
+				pg_log_error("this build does not support sync method \"%s\"",
+							 "syncfs");
+				exit(EXIT_FAILURE);
+#else
+				/*
+				 * On Linux, we don't have to open every single file one by
+				 * one.  We can use syncfs() to sync the whole filesystem.
+				 */
+				do_syncfs(dir);
+#endif							/* HAVE_SYNCFS */
+			}
+			break;
+
+		case DATA_DIR_SYNC_METHOD_FSYNC:
 			{
 				/*
-	 * If possible, hint to the kernel that we're soon going to fsync the data
-	 * directory and its contents.
+				 * If possible, hint to the kernel that we're soon going to
+				 * fsync the data directory and its contents.
 				 */
 #ifdef PG_FLUSH_DATA_WORKS
 				walkdir(dir, pre_sync_fname, false);
@@ -133,6 +249,9 @@ fsync_dir_recurse(const char *dir)
 
 				walkdir(dir, fsync_fname, false);
 			}
+			break;
+	}
+}
 
 /*
  * walkdir: recursively walk a directory, applying the action to each

src/include/common/file_utils.h

@@ -34,8 +34,9 @@ struct iovec;					/* avoid including port/pg_iovec.h here */
 
 #ifdef FRONTEND
 extern int	fsync_fname(const char *fname, bool isdir);
-extern void fsync_pgdata(const char *pg_data, int serverVersion);
-extern void fsync_dir_recurse(const char *dir);
+extern void sync_pgdata(const char *pg_data, int serverVersion,
+						DataDirSyncMethod sync_method);
+extern void sync_dir_recurse(const char *dir, DataDirSyncMethod sync_method);
 extern int	durable_rename(const char *oldfile, const char *newfile);
 extern int	fsync_parent_path(const char *fname);
 #endif