Add logic to load data in chunks

[bobbingwide]

The REST API works better when data is requested in chunks. But you can't set posts_per_page to -1 and you can't set it to an arbitrarily large number in the hope that it will be big enough.

The original logic to load 31 posts_per_page for the s-letter and b-letter taxonomies doesn't work for b-letter ( see #4 ) and the logic to load s-words or b-words when an s-letter or b-letter has been selected also fails since it only loads 10 posts and that's not enough.

We need to implement the ability to load mutiple pages of results.

[bobbingwide]

The first part - load the b-letter in chunks ( 10 at a time ) - was successful so now we need to apply the solution to other areas.

The design is going to change slightly. When the user selects a second letter then the list of bigrams is displayed showing both the s-word and the b-word in each bigram; one list for both rather than one each.

S	B
a b c	a b c

Scalped Brave, Scandinavian Blonde, Scenic Brittany

• [ ] change loadsletters() to work in chunks
• [ ] change onsletter() and onbletter() to load the full set for the selected letter populating sb_posts regardless of which letter was selected.
• [ ] remove redundant code - loadallswords(), loadbwords() etc.

Additionally,

• [ ] We need a method to stop the loading when another item is selected.
• [ ] And it would be nice to be able to store everything that's been loaded previously.

[bobbingwide]

Note: On my development manchine the performance of the paginated queries to list the items with a selected s-letter or b-letter is very poor. Currently averaging over 2 seconds. How can it be sped up? All we need initially is the title and the post ID.

Action	Range	Tracing disabled	Notes
original code	1.9 - 2.3 secs	1.6-1.9	Time for /wp/v2/bigram/s-letter=nnn&_embed=true&page=p
Remove _embed=true	0.5 - 0.7 secs	0.3-0.5	Per call
Set per_page=20	0.7	0.4-0.5	Per call
Set per_page=50	0.9 - 1.1 secs	0.7 - 0.8	Per call
Set per_page=100	1.4 - 1.9	1.1 - 1.3	Per call

[bobbingwide]

The solution for this issue has been implemented. The code is live on http://bigram.co.uk. The Additional items below will be handled in separate issues.

• We need a method to stop the loading when another item is selected.
• And it would be nice to be able to store everything that's been loaded previously.