Fix page and ptrack backup. It is necessary to backup only changed relations

src/backup.c

@@ -1939,7 +1939,8 @@ backup_files(void *arg)
 				/* backup block by block if datafile AND not compressed by cfs*/
 				if (!backup_data_file(arguments->from_root,
 									  arguments->to_root, file,
-									  arguments->prev_backup_start_lsn))
+									  arguments->prev_backup_start_lsn,
+									  current.backup_mode))
 				{
 					file->write_size = BYTES_INVALID;
 					elog(LOG, "File \"%s\" was not copied to backup", file->path);

src/data.c

@@ -282,7 +282,8 @@ backup_data_page(pgFile *file, XLogRecPtr prev_backup_start_lsn,
  */
 bool
 backup_data_file(const char *from_root, const char *to_root,
-				 pgFile *file, XLogRecPtr prev_backup_start_lsn)
+				 pgFile *file, XLogRecPtr prev_backup_start_lsn,
+				 BackupMode backup_mode)
 {
 	char			to_path[MAXPGPATH];
 	FILE			*in;
@@ -292,6 +293,17 @@ backup_data_file(const char *from_root, const char *to_root,
 	int n_blocks_skipped = 0;
 	int n_blocks_read = 0;
 
+	if ((backup_mode == BACKUP_MODE_DIFF_PAGE ||
+		backup_mode == BACKUP_MODE_DIFF_PTRACK) &&
+		file->pagemap.bitmapsize == 0)
+	{
+		/*
+		 * There are no changed blocks since last backup. We want make
+		 * incremental backup, so we should exit.
+		 */
+		return false;
+	}
+
 	/* reset size summary */
 	file->read_size = 0;
 	file->write_size = 0;

src/pg_probackup.h

@@ -413,7 +413,8 @@ extern int pgFileCompareSize(const void *f1, const void *f2);
 
 /* in data.c */
 extern bool backup_data_file(const char *from_root, const char *to_root,
-							 pgFile *file, XLogRecPtr prev_backup_start_lsn);
+							 pgFile *file, XLogRecPtr prev_backup_start_lsn,
+							 BackupMode backup_mode);
 extern void restore_data_file(const char *from_root, const char *to_root,
 							  pgFile *file, pgBackup *backup);
 extern bool copy_file(const char *from_root, const char *to_root,