If you're using memcached already you could store the number in it and
update it only when a user logs in/out. If no one is logging in/out, the
number isn't changing.

If your site is so popular that hundreds of users are logging in every
second you might want to change the logic so that the process to update the
count only does so when it has expired from the cache and give it a short
expiry time. At that point you probably would want each machine to track its
own number to avoid frequent distribution costs.

In the end I think you're going to have to get comfortable with the idea
that the number will never be exact. If you want exact, you have to pay for


Reply via email to