Who-to-follow suggestions join the fast lane
The sidebar's who-to-follow picks used to take minutes if you followed a few thousand people. A new anti join puts the same names on screen in a quarter of a second.
You click the refresh arrow in the who-to-follow box and the next three names are already there. One or two are popular accounts picked from the 20 most followed, and the rest are people your follows follow. No spinner, no half-drawn list. Before this release, that same click could sit there long enough for you to give up and close the tab.
Credit goes to chrisgocode, who rebuilt the check that keeps the popular picks from repeating names you already know. The old query handed Postgres a list of everyone your follows follow and tested every candidate against it. That meant 120,552 names for someone following 2,000 people, run across 50,000 candidates. The new query asks, for each candidate, whether anyone you follow follows them, and Postgres answers with an anti join. That took the sidebar request from 149,939 milliseconds to 250, and the database work alone from 114.6 seconds to 0.156.
There is one catch. Only the popular half of the list gets the new treatment. The other half still counts, for every candidate, how many of your follows follow them, so a big follow graph still reads the entire follows-of-follows table on every request. Follow a few thousand people and that count is now the expensive part.