Sync pg_dump and pg_dumpall output

Before exiting any files are fsync'ed. A --no-sync option is also
provided for a faster exit if desired.

Michael Paquier.

Reviewed by Albe Laurenz

Discussion: https://postgr.es/m/CAB7nPqS1uZ=Ov+UruW6jr3vB-S_DLVMPc0dQpV-fTDjmm0ZQMg@mail.gmail.com

Author: adunstan

doc/src/sgml/ref/pg_dump.sgml

@@ -859,6 +859,20 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--no-sync</option></term>
+      <listitem>
+       <para>
+        By default, <command>pg_dump</command> will wait for all files
+        to be written safely to disk.  This option causes
+        <command>pg_dump</command> to return without waiting, which is
+        faster, but means that a subsequent operating system crash can leave
+        the dump corrupt.  Generally, this option is useful for testing
+        but should not be used when dumping data from production installation.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>--quote-all-identifiers</></term>
       <listitem>

doc/src/sgml/ref/pg_dumpall.sgml

@@ -354,6 +354,20 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--no-sync</option></term>
+      <listitem>
+       <para>
+        By default, <command>pg_dumpall</command> will wait for all files
+        to be written safely to disk.  This option causes
+        <command>pg_dumpall</command> to return without waiting, which is
+        faster, but means that a subsequent operating system crash can leave
+        the dump corrupt.  Generally, this option is useful for testing
+        but should not be used when dumping data from production installation.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>--no-tablespaces</option></term>
       <listitem>

src/bin/pg_dump/pg_backup.h

@@ -276,7 +276,7 @@ extern Archive *OpenArchive(const char *FileSpec, const ArchiveFormat fmt);
 
 /* Create a new archive */
 extern Archive *CreateArchive(const char *FileSpec, const ArchiveFormat fmt,
-			  const int compression, ArchiveMode mode,
+			  const int compression, bool dosync, ArchiveMode mode,
 			  SetupWorkerPtr setupDumpWorker);
 
 /* The --list option */

src/bin/pg_dump/pg_backup_archiver.c

@@ -54,7 +54,8 @@ static const char *modulename = gettext_noop("archiver");
 
 
 static ArchiveHandle *_allocAH(const char *FileSpec, const ArchiveFormat fmt,
-	 const int compression, ArchiveMode mode, SetupWorkerPtr setupWorkerPtr);
+	 const int compression, bool dosync, ArchiveMode mode,
+	 SetupWorkerPtr setupWorkerPtr);
 static void _getObjectDescription(PQExpBuffer buf, TocEntry *te,
 					  ArchiveHandle *AH);
 static void _printTocEntry(ArchiveHandle *AH, TocEntry *te, bool isData, bool acl_pass);
@@ -202,10 +203,12 @@ setupRestoreWorker(Archive *AHX)
 /* Public */
 Archive *
 CreateArchive(const char *FileSpec, const ArchiveFormat fmt,
-	 const int compression, ArchiveMode mode, SetupWorkerPtr setupDumpWorker)
+			  const int compression, bool dosync, ArchiveMode mode,
+			  SetupWorkerPtr setupDumpWorker)
 
 {
-	ArchiveHandle *AH = _allocAH(FileSpec, fmt, compression, mode, setupDumpWorker);
+	ArchiveHandle *AH = _allocAH(FileSpec, fmt, compression, dosync,
+								 mode, setupDumpWorker);
 
 	return (Archive *) AH;
 }
@@ -215,7 +218,7 @@ CreateArchive(const char *FileSpec, const ArchiveFormat fmt,
 Archive *
 OpenArchive(const char *FileSpec, const ArchiveFormat fmt)
 {
-	ArchiveHandle *AH = _allocAH(FileSpec, fmt, 0, archModeRead, setupRestoreWorker);
+	ArchiveHandle *AH = _allocAH(FileSpec, fmt, 0, true, archModeRead, setupRestoreWorker);
 
 	return (Archive *) AH;
 }
@@ -2269,7 +2272,8 @@ _discoverArchiveFormat(ArchiveHandle *AH)
  */
 static ArchiveHandle *
 _allocAH(const char *FileSpec, const ArchiveFormat fmt,
-	  const int compression, ArchiveMode mode, SetupWorkerPtr setupWorkerPtr)
+		 const int compression, bool dosync, ArchiveMode mode,
+		 SetupWorkerPtr setupWorkerPtr)
 {
 	ArchiveHandle *AH;
 
@@ -2323,6 +2327,7 @@ _allocAH(const char *FileSpec, const ArchiveFormat fmt,
 
 	AH->mode = mode;
 	AH->compression = compression;
+	AH->dosync = dosync;
 
 	memset(&(AH->sqlparse), 0, sizeof(AH->sqlparse));
 

src/bin/pg_dump/pg_backup_archiver.h

@@ -312,6 +312,7 @@ struct _archiveHandle
 								 * values for compression: -1
 								 * Z_DEFAULT_COMPRESSION 0	COMPRESSION_NONE
 								 * 1-9 levels for gzip compression */
+	bool		dosync;			/* data requested to be synced on sight */
 	ArchiveMode mode;			/* File mode - r or w */
 	void	   *formatData;		/* Header data specific to file format */
 

src/bin/pg_dump/pg_backup_custom.c

@@ -28,6 +28,7 @@
 #include "compress_io.h"
 #include "parallel.h"
 #include "pg_backup_utils.h"
+#include "common/file_utils.h"
 
 /*--------
  * Routines in the format interface
@@ -721,6 +722,10 @@ _CloseArchive(ArchiveHandle *AH)
 	if (fclose(AH->FH) != 0)
 		exit_horribly(modulename, "could not close archive file: %s\n", strerror(errno));
 
+	/* Sync the output file if one is defined */
+	if (AH->dosync && AH->mode == archModeWrite && AH->fSpec)
+		(void) fsync_fname(AH->fSpec, false, progname);
+
 	AH->FH = NULL;
 }
 

src/bin/pg_dump/pg_backup_directory.c

@@ -37,6 +37,7 @@
 #include "compress_io.h"
 #include "parallel.h"
 #include "pg_backup_utils.h"
+#include "common/file_utils.h"
 
 #include <dirent.h>
 #include <sys/stat.h>
@@ -593,6 +594,13 @@ _CloseArchive(ArchiveHandle *AH)
 		WriteDataChunks(AH, ctx->pstate);
 
 		ParallelBackupEnd(AH, ctx->pstate);
+
+		/*
+		 * In directory mode, there is no need to sync all the entries
+		 * individually. Just recurse once through all the files generated.
+		 */
+		if (AH->dosync)
+			fsync_dir_recurse(ctx->directory, progname);
 	}
 	AH->FH = NULL;
 }

src/bin/pg_dump/pg_backup_tar.c

@@ -33,6 +33,7 @@
 #include "pg_backup_tar.h"
 #include "pg_backup_utils.h"
 #include "pgtar.h"
+#include "common/file_utils.h"
 #include "fe_utils/string_utils.h"
 
 #include <sys/stat.h>
@@ -901,6 +902,10 @@ _CloseArchive(ArchiveHandle *AH)
 			if (fputc(0, ctx->tarFH) == EOF)
 				WRITE_ERROR_EXIT;
 		}
+
+		/* Sync the output file if one is defined */
+		if (AH->dosync && AH->fSpec)
+			(void) fsync_fname(AH->fSpec, false, progname);
 	}
 
 	AH->FH = NULL;

src/bin/pg_dump/pg_dump.c

@@ -89,6 +89,8 @@ typedef enum OidOptions
 /* global decls */
 bool		g_verbose;			/* User wants verbose narration of our
 								 * activities. */
+static bool dosync = true;		/* Issue fsync() to make dump durable
+								 * on disk. */
 
 /* subquery used to convert user ID (eg, datdba) to user name */
 static const char *username_subquery;
@@ -353,6 +355,7 @@ main(int argc, char **argv)
 		{"no-security-labels", no_argument, &dopt.no_security_labels, 1},
 		{"no-synchronized-snapshots", no_argument, &dopt.no_synchronized_snapshots, 1},
 		{"no-unlogged-table-data", no_argument, &dopt.no_unlogged_table_data, 1},
+		{"no-sync", no_argument, NULL, 7},
 
 		{NULL, 0, NULL, 0}
 	};
@@ -533,6 +536,10 @@ main(int argc, char **argv)
 				dumpsnapshot = pg_strdup(optarg);
 				break;
 
+			case 7:				/* no-sync */
+				dosync = false;
+				break;
+
 			default:
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 				exit_nicely(1);
@@ -632,8 +639,8 @@ main(int argc, char **argv)
 		exit_horribly(NULL, "parallel backup only supported by the directory format\n");
 
 	/* Open the output file */
-	fout = CreateArchive(filename, archiveFormat, compressLevel, archiveMode,
-						 setupDumpWorker);
+	fout = CreateArchive(filename, archiveFormat, compressLevel, dosync,
+						 archiveMode, setupDumpWorker);
 
 	/* Make dump options accessible right away */
 	SetArchiveOptions(fout, &dopt, NULL);
@@ -914,6 +921,7 @@ help(const char *progname)
 	printf(_("  -V, --version                output version information, then exit\n"));
 	printf(_("  -Z, --compress=0-9           compression level for compressed formats\n"));
 	printf(_("  --lock-wait-timeout=TIMEOUT  fail after waiting TIMEOUT for a table lock\n"));
+	printf(_("  --no-sync                    do not wait for changes to be written safely to disk\n"));
 	printf(_("  -?, --help                   show this help, then exit\n"));
 
 	printf(_("\nOptions controlling the output content:\n"));

src/bin/pg_dump/pg_dumpall.c

@@ -22,6 +22,7 @@
 
 #include "dumputils.h"
 #include "pg_backup.h"
+#include "common/file_utils.h"
 #include "fe_utils/string_utils.h"
 
 /* version string we expect back from pg_dump */
@@ -63,6 +64,7 @@ static PQExpBuffer pgdumpopts;
 static char *connstr = "";
 static bool skip_acls = false;
 static bool verbose = false;
+static bool dosync = true;
 
 static int	binary_upgrade = 0;
 static int	column_inserts = 0;
@@ -127,6 +129,7 @@ main(int argc, char *argv[])
 		{"role", required_argument, NULL, 3},
 		{"use-set-session-authorization", no_argument, &use_setsessauth, 1},
 		{"no-security-labels", no_argument, &no_security_labels, 1},
+		{"no-sync", no_argument, NULL, 4},
 		{"no-unlogged-table-data", no_argument, &no_unlogged_table_data, 1},
 		{"no-role-passwords", no_argument, &no_role_passwords, 1},
 
@@ -297,6 +300,11 @@ main(int argc, char *argv[])
 				appendShellString(pgdumpopts, use_role);
 				break;
 
+			case 4:
+				dosync = false;
+				appendPQExpBufferStr(pgdumpopts, " --no-sync");
+				break;
+
 			default:
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 				exit_nicely(1);
@@ -549,8 +557,14 @@ main(int argc, char *argv[])
 	fprintf(OPF, "--\n-- PostgreSQL database cluster dump complete\n--\n\n");
 
 	if (filename)
+	{
 		fclose(OPF);
 
+		/* sync the resulting file, errors are not fatal */
+		if (dosync)
+			(void) fsync_fname(filename, false, progname);
+	}
+
 	exit_nicely(0);
 }
 
@@ -586,6 +600,7 @@ help(void)
 	printf(_("  --if-exists                  use IF EXISTS when dropping objects\n"));
 	printf(_("  --inserts                    dump data as INSERT commands, rather than COPY\n"));
 	printf(_("  --no-security-labels         do not dump security label assignments\n"));
+	printf(_("  --no-sync                    do not wait for changes to be written safely to disk\n"));
 	printf(_("  --no-tablespaces             do not dump tablespace assignments\n"));
 	printf(_("  --no-unlogged-table-data     do not dump unlogged table data\n"));
 	printf(_("  --no-role-passwords          do not dump passwords for roles\n"));

src/common/file_utils.c

@@ -115,6 +115,25 @@ fsync_pgdata(const char *pg_data,
 	walkdir(pg_tblspc, fsync_fname, true, progname);
 }
 
+/*
+ * Issue fsync recursively on the given directory and all its contents.
+ *
+ * This is a convenient wrapper on top of walkdir().
+ */
+void
+fsync_dir_recurse(const char *dir, const char *progname)
+{
+	/*
+	 * 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, progname);
+#endif
+
+	walkdir(dir, fsync_fname, false, progname);
+}
+
 /*
  * walkdir: recursively walk a directory, applying the action to each
  * regular file and directory (including the named directory itself).

src/include/common/file_utils.h

@@ -19,6 +19,7 @@ extern int fsync_fname(const char *fname, bool isdir,
 					   const char *progname);
 extern void fsync_pgdata(const char *pg_data, const char *progname,
 						 int serverVersion);
+extern void fsync_dir_recurse(const char *dir, const char *progname);
 extern int durable_rename(const char *oldfile, const char *newfile,
 						  const char *progname);
 extern int fsync_parent_path(const char *fname, const char *progname);