I mostly used one type of card per note, so it was essentially 21,000 notes. I say was, because I haven’t used the deck for many years. I rely more on using the language these days and don’t feel a strong need for this type of reviewing. I do study character writings in Skritter though, maintaining the 5000 most common characters or so!

Does this refer to cards or notes? Also, I curious as to where your deck is at now…

I realize this is an old thread Google sent me to, but it’s timeless. I always thought that the recommendations to nuke a deck were misguided, and Anki actually has everything built in to deal with the issues of a big deck.
There are leeches to identify which words you spend too much time on. Take them serious. My most common action is to delete them, that’s my freedom!
We can suspend cards we only want to keep for reference to look them up later. Suspended cards won’t take any time at all.
And finally we have spacing to deal with changed needs. Sure my needs are different now, but words I know quickly get to 10 years or so and really won’t take much time. If they did take much time, they’d quickly turn up as leeches, and I find myself deleting words rather than marking them as wrong when I realize this is a word I no longer want.

In sum, prune as you go along…

First, I assume we’re talking about Anki here? If that’s the case, go to browse cards, select all the cards you don’t want (you can select by tag, so select all chapters you don’t want to learn yet), click suspend. Done. If you want to study the suspended cards later, unsuspend them the same way. I’m quite sure this is in the manual, though.

What do you mean by suspend everything? Where would I do that, from what screen?
What I ended up doing was using “custom study”, then choosing the study by tags. I specified which tags I wanted (Lesson 1) and told it which I didn’t want (the other lessons). If there is a better way, let me know.

I usually just suspend everything and then gradually unsuspend as I progress through the chapters.