A live comment system loads over AJAX, which means it never comes from the page cache. Your most popular posts become your least cacheable ones.
Everything follows from comments arriving separately from the article, on a request the cache cannot answer.
The article is served from cache and the thread underneath is fetched live. That second request is where the real load sits, and it is sized for rather than ignored.
A thread with two thousand replies is a threaded query with sorting, voting and pagination on top. Those lookups are indexed instead of scanning every comment on the site.
An open comment form attracts automated submissions constantly. They are turned away cheaply, so the volume is bandwidth rather than a database write and a moderation queue.
Real-time threads ask the server for new comments repeatedly. That polling is the hidden traffic on a busy post, and it is planned for as its own load.
A decade of discussion is worth as much as the posts. It is backed up daily rather than treated as something regenerable.
On most sites a popular page is cheap because it is cached. With a live comment system, popularity means more uncached AJAX requests per view, not fewer.
The measure is loading a long thread with voting and sorting applied, because that is the request every reader on a popular post makes.
The comment system is a second application living under the article, and it is the one carrying the load.
| Setting | What we do | Why |
|---|---|---|
| AJAX comment requests | Sized as primary traffic rather than as an extra | The article comes from cache and the thread does not, so on a popular post the uncached request is the one every reader makes. |
| Comment table indexing | Indexed for threading, sorting and votes together | A two-thousand-reply thread is a recursive query with ordering and vote counts applied, and without indexes it reads every comment on the site. |
| Spam rejection | Handled before a database write occurs | An open form receives automated submissions constantly, and letting each one reach the database turns background noise into a moderation queue and a write load. |
| Live polling | Accounted for as continuous background traffic | Real-time threads ask for updates on a timer, so a hundred readers on one post generate steady requests nobody sees in a pageview count. |
| Comment backups | Covered daily as content, not as plugin data | Years of discussion cannot be regenerated, and it is routinely the part of a site nobody checked was included. |
Every plan includes free migration, daily backups, SSL and 24/7 support.
Move the site across — migration is free, every comment included.