Add wal_sync_method=fdatasync for Windows.

Windows 10 gained support for flushing NTFS files with fdatasync()
semantics.  The main advantage over open_datasync (in Windows API terms
FILE_FLAG_WRITE_THROUGH) is that the latter does not flush SATA drive
caches.  The default setting is not changed, so users have to opt in to
this.

Discussion: https://postgr.es/m/CA%2BhUKGJZJVO%3DiX%2Beb-PXi2_XS9ZRqnn_4URh0NUQOwt6-_51xQ%40mail.gmail.com

configure

@@ -17132,6 +17132,12 @@ fi
  ;;
 esac
 
+  case " $LIBOBJS " in
+  *" fdatasync.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS fdatasync.$ac_objext"
+ ;;
+esac
+
   case " $LIBOBJS " in
   *" kill.$ac_objext "* ) ;;
   *) LIBOBJS="$LIBOBJS kill.$ac_objext"

configure.ac

@@ -1988,6 +1988,7 @@ if test "$PORTNAME" = "win32"; then
   AC_CHECK_FUNCS(_configthreadlocale)
   AC_REPLACE_FUNCS(gettimeofday)
   AC_LIBOBJ(dirmod)
+  AC_LIBOBJ(fdatasync)
   AC_LIBOBJ(kill)
   AC_LIBOBJ(open)
   AC_LIBOBJ(system)

doc/src/sgml/wal.sgml

@@ -108,7 +108,8 @@
         <literal>open_datasync</literal> (the default), write caching can be disabled
         by unchecking <literal>My Computer\Open\<replaceable>disk drive</replaceable>\Properties\Hardware\Properties\Policies\Enable write caching on the disk</literal>.
         Alternatively, set <varname>wal_sync_method</varname> to
-        <literal>fsync</literal> or <literal>fsync_writethrough</literal>, which prevent
+        <literal>fdatasync</literal> (NTFS only), <literal>fsync</literal> or
+        <literal>fsync_writethrough</literal>, which prevent
         write caching.
       </para>
     </listitem>

src/include/c.h

@@ -1290,7 +1290,7 @@ typedef union PGAlignedXLogBlock
  * standard C library.
  */
 
-#if defined(HAVE_FDATASYNC) && !HAVE_DECL_FDATASYNC
+#if !HAVE_DECL_FDATASYNC
 extern int	fdatasync(int fildes);
 #endif
 

src/include/port/win32_port.h

@@ -83,6 +83,12 @@
 #define HAVE_FSYNC_WRITETHROUGH
 #define FSYNC_WRITETHROUGH_IS_FSYNC
 
+/*
+ * We have a replacement for fdatasync() in src/port/fdatasync.c, which is
+ * unconditionally used by MSVC and Mingw builds.
+ */
+#define HAVE_FDATASYNC
+
 #define USES_WINSOCK
 
 /*

src/include/port/win32ntdll.h

@@ -23,9 +23,17 @@
 #include <ntstatus.h>
 #include <winternl.h>
 
-typedef NTSTATUS (__stdcall * RtlGetLastNtStatus_t) (void);
+#ifndef FLUSH_FLAGS_FILE_DATA_SYNC_ONLY
+#define FLUSH_FLAGS_FILE_DATA_SYNC_ONLY 0x4
+#endif
+
+typedef NTSTATUS (__stdcall *RtlGetLastNtStatus_t) (void);
+typedef ULONG (__stdcall *RtlNtStatusToDosError_t) (NTSTATUS);
+typedef NTSTATUS (__stdcall *NtFlushBuffersFileEx_t) (HANDLE, ULONG, PVOID, ULONG, PIO_STATUS_BLOCK);
 
 extern PGDLLIMPORT RtlGetLastNtStatus_t pg_RtlGetLastNtStatus;
+extern PGDLLIMPORT RtlNtStatusToDosError_t pg_RtlNtStatusToDosError;
+extern PGDLLIMPORT NtFlushBuffersFileEx_t pg_NtFlushBuffersFileEx;
 
 extern int	initialize_ntdll(void);
 

src/port/fdatasync.c

@@ -0,0 +1,53 @@
+/*-------------------------------------------------------------------------
+ *
+ * fdatasync.c
+ *	   Win32 fdatasync() replacement
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ *
+ * src/port/fdatasync.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#define UMDF_USING_NTSTATUS
+
+#ifdef FRONTEND
+#include "postgres_fe.h"
+#else
+#include "postgres.h"
+#endif
+
+#include "port/win32ntdll.h"
+
+int
+fdatasync(int fd)
+{
+	IO_STATUS_BLOCK iosb;
+	NTSTATUS	status;
+	HANDLE		handle;
+
+	handle = (HANDLE) _get_osfhandle(fd);
+	if (handle == INVALID_HANDLE_VALUE)
+	{
+		errno = EBADF;
+		return -1;
+	}
+
+	if (initialize_ntdll() < 0)
+		return -1;
+
+	memset(&iosb, 0, sizeof(iosb));
+	status = pg_NtFlushBuffersFileEx(handle,
+									 FLUSH_FLAGS_FILE_DATA_SYNC_ONLY,
+									 NULL,
+									 0,
+									 &iosb);
+
+	if (NT_SUCCESS(status))
+		return 0;
+
+	_dosmaperr(pg_RtlNtStatusToDosError(status));
+	return -1;
+}

src/port/win32ntdll.c

@@ -20,6 +20,8 @@
 #include "port/win32ntdll.h"
 
 RtlGetLastNtStatus_t pg_RtlGetLastNtStatus;
+RtlNtStatusToDosError_t pg_RtlNtStatusToDosError;
+NtFlushBuffersFileEx_t pg_NtFlushBuffersFileEx;
 
 typedef struct NtDllRoutine
 {
@@ -28,7 +30,9 @@ typedef struct NtDllRoutine
 } NtDllRoutine;
 
 static const NtDllRoutine routines[] = {
-	{"RtlGetLastNtStatus", (pg_funcptr_t *) &pg_RtlGetLastNtStatus}
+	{"RtlGetLastNtStatus", (pg_funcptr_t *) &pg_RtlGetLastNtStatus},
+	{"RtlNtStatusToDosError", (pg_funcptr_t *) &pg_RtlNtStatusToDosError},
+	{"NtFlushBuffersFileEx", (pg_funcptr_t *) &pg_NtFlushBuffersFileEx}
 };
 
 static bool initialized;

src/tools/msvc/Mkvcbuild.pm

@@ -99,7 +99,8 @@ sub mkvcbuild
 	$solution = CreateSolution($vsVersion, $config);
 
 	our @pgportfiles = qw(
-	  chklocale.c explicit_bzero.c fls.c getpeereid.c getrusage.c inet_aton.c
+	  chklocale.c explicit_bzero.c fls.c fdatasync.c
+	  getpeereid.c getrusage.c inet_aton.c
 	  getaddrinfo.c gettimeofday.c inet_net_ntop.c kill.c open.c
 	  snprintf.c strlcat.c strlcpy.c dirmod.c noblock.c path.c
 	  dirent.c dlopen.c getopt.c getopt_long.c link.c

src/tools/msvc/Solution.pm

@@ -257,7 +257,7 @@ sub GenerateFiles
 		HAVE_EDITLINE_READLINE_H                    => undef,
 		HAVE_EXECINFO_H                             => undef,
 		HAVE_EXPLICIT_BZERO                         => undef,
-		HAVE_FDATASYNC                              => undef,
+		HAVE_FDATASYNC                              => 1,
 		HAVE_FLS                                    => undef,
 		HAVE_FSEEKO                                 => 1,
 		HAVE_FUNCNAME__FUNC                         => undef,