Does not work well with large files

It's not a very well written issue as is, but just want to acknowledge this significant limitation as soon as possible. I see app crashing on files with 100 000 lines. Perhaps I'll try to grow a list here of related and concrete issues, or it is fine to file new more specific issues.

Start by reproducing the crash with a 100,000-line file in the app and record the failure details. Trace the file-loading path to identify the limiting operation; done means the app can open and work with files of that size without crashing.

Written by the indexing model from the issue text.