Performance issue when keys are long and similar

[whudwl]

Not really an issue, but something I encountered.
I'm using elfeed to store posts from a quite active online forum.
I've noticed that the performance is getting out of hand (8 seconds to start elfeed) even if I have only about 9000 entries. and index size is only about 5MB.
It seems to me this is because all entries come from the same source, so all the keys look very similar (differ only at the very end), this costs equal to take longer?, a key for an entry would look like:

("https://example.com/something/something/feed.xml" . "https://example.com/something/something/POSTID")

I unloaded the elfeed-db, opened the index file and replaced every https://example.com/something/something/POSTID in the keys with just POSTID (I hope this is OK?) , and elfeed lighting fast again.