[manut999]

Problem

Deleting a book is very slow on large libraries. On mine (~208k books) every single delete took ~40 s, and since it runs in the web process the whole UI stops responding for that time (healthcheck timeouts, unhealthy). Resolving 19 duplicate groups took 785 s.

delete_whole_book() calls modify_database_object() for authors, tags, series, languages and publishers, which ends in remove_objects():

db_book_object.remove(del_element)
if len(del_element.books) == 0:
    db_session.delete(del_element)

len(del_element.books) loads every book linked to that element just to see whether the list is empty. Because all Books relationships are lazy='selectin', each of those books also pulls its authors, tags, data, comments, identifiers, … For the language deu that is 189,034 books in my library — on every delete.

Confirmed with py-spy dump during a duplicate resolution run:

LazyLoader._emit_lazyload (sqlalchemy/orm/strategies.py:1152)
...
InstrumentedAttribute.__get__ (sqlalchemy/orm/attributes.py:569)
remove_objects (cps/editbooks.py:1979)
modify_database_object (cps/editbooks.py:2074)
delete_whole_book (cps/editbooks.py:1321)      # languages
auto_resolve_duplicates (cps/duplicates.py:1749)

The same applies to editing a book's metadata whenever a widely used tag/language/publisher is removed from it, and to deletes from the book page.

Fix

Flush the removed link, then ask the database whether any book still references the element:

db_session.flush()
still_used = (db_session.query(db.Books.id)
              .with_parent(del_element, type(del_element).books)
              .limit(1)
              .first())
if still_used is None:
    db_session.delete(del_element)

with_parent uses the existing books backref, so it works for authors, tags, series, languages, publishers and the multi-value custom column classes alike, without per-type code. The semantics are unchanged: the element is deleted exactly when no book links to it anymore.

Testing

On a copy of my metadata.db (190k books), using the real cps.db models and remove_objects():

case	before	after
remove language deu from a book	~40 s	0.00 s, deu kept
remove a tag that only this book had	—	0.00 s, tag deleted

Running patched in my instance since; duplicate resolution and manual deletes are now instant and the UI stays responsive.

🤖 Generated with Claude Code