The bad neighbour effect is when one site on a shared server uses up resources that other sites on that server need.
The bad neighbour effect (also called the noisy neighbour problem) happens on shared hosting, where many websites run on one physical server. If one of those sites suddenly uses far more CPU, memory or disk activity than usual, the others can slow down or stop responding, even though nothing is wrong with them.
Picture a block of flats sharing one hot water tank. If one flat runs every tap at once, everyone else gets a cold shower. On a server, the "hot water" is processing power, memory and disk speed.
What causes the bad neighbour effect
Common causes include:
- A traffic spike, such as a post going viral or a sale launch.
- Badly written plugins or scripts that run heavy database queries on every page.
- A site infected with malware that sends spam or attacks other servers.
- Bots crawling thousands of pages at once.
- A heavy cron job or backup running at peak time.
How the bad neighbour effect affects your website
You might notice slower page loads, a higher TTFB, timeouts in your admin area or brief errors. If a neighbour's site is sending spam, the server's shared IP address can end up on a blocklist, which hurts your email deliverability as well.
The tricky part is that these symptoms look the same as problems on your own site. If your site is slow but your own resource usage looks normal, a neighbour may be the cause.
How hosts prevent the bad neighbour effect
Good hosts don't rely on everyone behaving. They isolate accounts from each other:
- Per-account limits on CPU, memory and entry processes, so one account can't take over the server.
- Monitoring that flags accounts with unusual usage.
- Malware scanning and firewalls that stop infected sites from attacking or spamming.
- Sensible server density, so servers aren't packed with more sites than they can handle.
Bad neighbour effect vs your own limits
Being limited isn't the same as having a bad neighbour. If your site regularly hits its own CPU or memory limits, it's outgrown its plan. Options include adding a cache, optimising plugins, upgrading, or moving to a bigger plan or a VPS.
AblePage's plans step up from 1x performance on Lite to 4x on Elite, and every plan includes Imunify360 malware scanning and firewall.