backup: break one key scan when met delete version (tikv#6655)

Signed-off-by: luancheng <luancheng@pingcap.com>

src/storage/mvcc/reader/scanner/forward.rs

@@ -472,11 +472,15 @@ impl<S: Snapshot> ScanPolicy<S> for LatestEntryPolicy {
                         write: entry_write,
                     });
                 }
-                WriteType::Delete if self.output_delete => {
-                    break Some(TxnEntry::Commit {
-                        default: (Vec::new(), Vec::new()),
-                        write: (write_key.to_vec(), write_value.to_vec()),
-                    });
+                WriteType::Delete => {
+                    if self.output_delete {
+                        break Some(TxnEntry::Commit {
+                            default: (Vec::new(), Vec::new()),
+                            write: (write_key.to_vec(), write_value.to_vec()),
+                        });
+                    } else {
+                        break None;
+                    }
                 }
                 _ => {}
             }
@@ -1428,14 +1432,16 @@ mod latest_entry_tests {
 
         // Scanning entries in (10, 15] should get None
         check(15, 10, true, vec![]);
-        // Scanning entries without delete in (7, 10]  should get None
+        // Scanning entries without delete in (7, 10] should get None
         check(10, 7, false, vec![]);
-        // Scanning entries include delete in (7, 10]  should get entry_b_10
+        // Scanning entries include delete in (7, 10] should get entry_b_10
         check(10, 7, true, vec![&entry_b_10]);
         // Scanning entries include delete in (3, 10] should get a_7 and b_10
         check(10, 3, true, vec![&entry_a_7, &entry_b_10]);
         // Scanning entries in (0, 5] should get a_3 and b_1
         check(5, 0, true, vec![&entry_a_3, &entry_b_1]);
+        // Scanning entries without delete in (0, 10] should get a_7
+        check(10, 0, false, vec![&entry_a_7]);
     }
 }