Bug 24185: Make holds page fast when 'on shelf holds' set to 'If all unavailable'

Bug 24185: Make holds page fast when 'on shelf holds' set to 'If all unavailable'

When "reserve/request.pl -> C4/Reserves.pm::IsAvailableForItemLevelRequest" called many times with hundred of items and "on shelf holds" parameter set to "If all unavailable" for these items + patron, it goes slow.

It happens because in subloop it is checking if all items available so it is O(n^2) and it re-checks each time the same info for each item with repeating DB/data requests.

Fix:
The inner loop 1:1 picked out into separate subroutine and called outside of the loop, saving data in 'items_any_available' variable once, this variable passed to IsAvailableForItemLevelRequest to be used inside as the precalculated result.

This made algorithm O(n) instead of O(n^2) so there is noticeable speed increase.

How to reproduce:

1) on freshly installed kohadevbox create/import one book,
remember that biblionumber for later use it in down below,

2) add 100 items for that book for some library,

3) find some patron, that patron's card number we will
use as a borrower down below to open holds page,

4) check for the rule or set up a single circulation rule
in admin "/cgi-bin/koha/admin/smart-rules.pl",
that rule should match above book items/library/patron,
check that rule to have a non-zero number of holds (total, daily, count) allowed,
and, IMPORTANT: set up "On shelf holds allowed" to "If all unavailable",
("item level holds" doesn't matter).

5) open "Home > Catalog > THAT_BOOK > Place a hold on THAT_BOOK" page
("holds" tab), and enter patron code in the search field,
or you can create a direct link by yourself, for example, in my case it was:
/cgi-bin/koha/reserve/request.pl?biblionumber=4&findborrower=23529000686353

6) it should be pretty long page generation time on old code, densely increasing for every hundred items added. In the case of this solution, it's fast, and time increases a little only, linear.

I tested on my computer in VirtualBox for page generation times,
did 3-5 runs for same case to check if results are stable, and got such values:

(old code):
  100 items:    50 seconds
  200 items:   3.2 minutes
  300 items:   7.3 minutes

(version with fix):
  100 items:   4.4 seconds
  200 items:   7.5 seconds
  300 items:  10.4 seconds

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>