Database mdl_user count: 167,065

Webservice call to retrieve all users starting from B (around 10,000+ users) seems to have drastically increased in time in processing.

Using the core_user_get_users WS call on 4.0 version with took 2.6 minutes to complete

[YOURURL]/webservice/rest/server.php?wstoken=[YOURTOKEN]&moodlewsrestformat=json&wsfunction=core_user_get_users&criteria%5B0%5D%5Bkey%5D=lastname&criteria%5B0%5D%5Bvalue%5D=B%25

The same ws call using 4.1 took 7.6 minutes using the same database/same number of records.

I have checked the SQL at user/externallib.php and seems like there are no changes from 4.0 to 4.1. So something is definitely causing the huge jump of processing:

4.0 = 2.6minutes
versus
4.1 = 7.6minutes