ldb: set `total_order_seek` for scans (#5066)

Summary:
Without `total_order_seek=true`, using this command with `prefix_extractor` set skips over lots of keys.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5066

Differential Revision: D14425967

Pulled By: sagar0

fbshipit-source-id: f6f142733258d92604f920615be9266e1fe797f8

tools/ldb_cmd.cc

@@ -1469,7 +1469,9 @@ void DBDumperCommand::DoDumpCommand() {
   }
 
   // Setup key iterator
-  Iterator* iter = db_->NewIterator(ReadOptions(), GetCfHandle());
+  ReadOptions scan_read_opts;
+  scan_read_opts.total_order_seek = true;
+  Iterator* iter = db_->NewIterator(scan_read_opts, GetCfHandle());
   Status st = iter->status();
   if (!st.ok()) {
     exec_state_ =
@@ -2325,7 +2327,9 @@ void ScanCommand::DoCommand() {
   }
 
   int num_keys_scanned = 0;
-  Iterator* it = db_->NewIterator(ReadOptions(), GetCfHandle());
+  ReadOptions scan_read_opts;
+  scan_read_opts.total_order_seek = true;
+  Iterator* it = db_->NewIterator(scan_read_opts, GetCfHandle());
   if (start_key_specified_) {
     it->Seek(start_key_);
   } else {