Sirsi explanation of the sort process:
Specifies the number of items to include in a sorted search. When a library user performs a search, the system returns all of the closest matches ranked by relevance. The Sort By drop-down list lets the user sort the by publication date (ascending or descending order), title, or author. When the sort is selected, the system takes the number of most relevant matches from the search that you specify here and sorts them by the selected option. For example, if you leave the number of items to sort at 300 (the default), the system sorts the first 300 relevant titles by the Sort By option selected. If you make the number higher, the system will take more time to sort the titles. When a library user types a new search term in the Search box and chooses Search, the system returns the items sorted by relevance rather than the sort order applied to the previous search. Sorting search results is not available for federated database searches.
Sirsi answer to changing the sort number:
The best thing you can do to improve the speed of sorting result sets in Enterprise/Portfolio is to reduce the number of records that are sorted. This is found in Manage Profiles, edit your profile and then change the Items to sort number in the Search Options sections. When a sort is done on search results, Enterprise will take the top this many results by relevance and sort this subset by the selected field. Note that sorting is inherently a non-linear process so sorting 200 results will take significantly more than twice as long as sorting 100 results. The maximum that you can enter into this field is 1000.
Another thing you can do is to reduce the size of the set to be sorted by reducing the number of fields on your search results screen. This is done in Manage Displays > Manage Search Result Displays. Edit the display you are using and remove any unneeded fields. To find which display you are using, go to Manage Profiles > Display Selection.
You will need to balance your desired result set size with your sorting performance requirements.
Sirsi customer answer on the Enterprise lists:
We first upped ours to 500 and now have it at 1000, and have been reluctant to go any higher—at that point, everyone’s searches don’t seem to be affected by the entire system getting bogged down by handling searches, but the time it takes to do a sort is noticeably longer than we wish it were but still mostly tolerable.