Why we did this originally[1]:
> Calculating the number of pages in a letter is quite slow. And the
> send yourself a test pages need to load _fast_. Since filling in
> placeholders is very unlikely to change the number of pages in the
> resultant letter, it’s pretty safe to cache that count, and makes the
> subsequent pages load a lot faster.
However things have changed since then:
- this journey is used for sending real letters, not just test ones
- we’re doing enough letters that even an unlikely discrepancy will (and
does) happen
- we cache the generation of the PDF now[2], so at least it’s not
generating the PDF twice, once for the preview and once for the page
count
- it’s no longer necessary to step through each address placeholder to
populate a one-off letter, so a little bit slower isn’t so bad
1. e7896f283a
2. c9c6271aa0/app/preview.py (L140)
2f79ef136d