My website has a high number of users, over 50k and I use Ajax Search Pro to search users. It is hosted on a high speed private server. However, the search is slow and I wanted to use the table index to index users, which I understand would make the search speedier. My issues is that I can not find how I can index users. Can you please assist on this ?
Unfortunately the index table only works with post type contents. The users database is indexed fairly well in general. For the maximum possible performance try selecting the least amount fields to search.
For that amount of users searching their display names should be more than sufficient to give a fairly big results pool: https://i.imgur.com/1m2cCh5.png
Turning off searching in user meta fields should have a great impact on the performance as well: https://i.imgur.com/kXNTAVL.png
Basically any field you can avoid searching will have an impact on the performance.