Interview Question for Software Engineer at Google:

The idea is to have a distributed local counters and a good way to combine the local counters into one global counter. Another key property is to combine the results of local counters asynchronously in order not to slow down the search time.

Each server should keep track of the total number of users, and perform "edits" to this number.

At a specified time interval, servers should synchronize their counter by transmitted their aggregated "edits" to the total number of users.

"Edits" are simply how much to add to the sum.