Improve copydir() code for the case that fsync is off.

We should avoid calling sync_file_range or posix_fadvise in this case,
since (a) we don't really care if the data gets synced, and might as
well save the kernel calls; (b) at least on Linux we know that the
kernel might block us until it's scheduled the write.

Also, avoid making a useless second traversal of the directory tree
if we're not actually going to call fsync(2) after all.

src/backend/storage/file/copydir.c

@@ -98,7 +98,11 @@ copydir(char *fromdir, char *todir, bool recurse)
 
 	/*
 	 * Be paranoid here and fsync all files to ensure the copy is really done.
+	 * But if fsync is disabled, we're done.
 	 */
+	if (!enableFsync)
+		return;
+
 	xldir = AllocateDir(todir);
 	if (xldir == NULL)
 		ereport(ERROR,
@@ -200,9 +204,9 @@ copy_file(char *fromfile, char *tofile)
 		/*
 		 * We fsync the files later but first flush them to avoid spamming the
 		 * cache and hopefully get the kernel to start writing them out before
-		 * the fsync comes.
+		 * the fsync comes.  Ignore any error, since it's only a hint.
 		 */
-		pg_flush_data(dstfd, offset, nbytes);
+		(void) pg_flush_data(dstfd, offset, nbytes);
 	}
 
 	if (close(dstfd))

src/backend/storage/file/fd.c

@@ -337,18 +337,22 @@ pg_fdatasync(int fd)
  * pg_flush_data --- advise OS that the data described won't be needed soon
  *
  * Not all platforms have sync_file_range or posix_fadvise; treat as no-op
- * if not available.
+ * if not available.  Also, treat as no-op if enableFsync is off; this is
+ * because the call isn't free, and some platforms such as Linux will actually
+ * block the requestor until the write is scheduled.
  */
 int
 pg_flush_data(int fd, off_t offset, off_t amount)
 {
+	if (enableFsync)
+	{
 #if defined(HAVE_SYNC_FILE_RANGE)
-	return sync_file_range(fd, offset, amount, SYNC_FILE_RANGE_WRITE);
+		return sync_file_range(fd, offset, amount, SYNC_FILE_RANGE_WRITE);
 #elif defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
-	return posix_fadvise(fd, offset, amount, POSIX_FADV_DONTNEED);
-#else
-	return 0;
+		return posix_fadvise(fd, offset, amount, POSIX_FADV_DONTNEED);
 #endif
+	}
+	return 0;
 }