Hiccups when closed channels are being forgotten

[michael1011]

When closed channels with lots of updates are being forgotten, the CLN RPC freezes until the deletion is done.

From @rustyrussell:

I strongly suspect it's this:
stmt = db_prepare_v2(w->db, SQL("DELETE FROM channel_htlcs "
"WHERE channel_id=?"));

This is because there's no index for that exact thing, so this causes a sweep of the entire table. Fix is obvious: add another index...

[whitslack]

Do you not have a unique index on (channel_id, channel_htlc_id, direction)? My channel_htlcs table has that index.

[michael1011]

Yes, that index exists. And even if it didn't, I wouldn't want to start creating indexes myself by hand

[whitslack]

Yes, that index exists.

So there would be nothing to gain by adding an index on solely channel_id. It would only slow down writes.