# My site slowed down overnight

> A site that suddenly takes eight seconds to open when it took two last week has not simply aged. Something changed, on a specific date, and finding that date is half the diagnosis. A slowdown that has always been there and one that appeared yesterday are not treated the same way at all.

- Source canonique : [https://allaux.fr/en/problemes/site-lent-depuis-hier](https://allaux.fr/en/problemes/site-lent-depuis-hier)
- Langue : EN
- Dernière mise à jour : 2026-09-30

## Direct answer

> Find the date it tipped before looking for the cause: the server access logs show at a glance whether traffic jumped or only response time rose. Then measure time to first byte on a simple page and on a catalogue page; if only the second drags, it is an SQL query. On PrestaShop, switch _PS_DEBUG_PROFILING_ on in config/defines.inc.php outside peak hours.

## Describing the slowdown precisely

- The browser sits on a blank page for several seconds before anything appears: the server is slow to answer.
- The page appears quickly but stays unusable, images arriving one by one: the problem is in what the page loads, not in the server.
- Only the admin area is slow; the shop your customers see behaves normally.
- The slowdown returns at a fixed hour, or only during your campaigns.

## Two very different slowdowns

The first figure to isolate is how long the server takes to send the first byte of the page, known as TTFB. As long as that stays within a few hundred milliseconds, the server is doing its job: the perceived slowness then comes from page weight, uncompressed images and third-party tracking or chat scripts. Those are two separate projects, with two separate budgets.

If the first byte instead takes several seconds, the problem sits upstream of rendering: too many or too heavy database queries, a disabled cache, an old PHP version, or a saturated server. On shared hosting, saturation can even come from another site sharing the same machine.

## Finding what changed

1. **Date the start** — Ask your team and check your analytics: the exact date of the switch guides everything else. One day, not one week.
2. **List that week’s changes** — A CMS, module or plugin update, a new advertising script, a theme change, a bulk product import, a change of hosting plan.
3. **Compare a simple page with a heavy one** — If the legal notice page is as slow as a category page, the cause is global. If only the category page suffers, it lies in the catalogue or the filters.
4. **Test outside peak hours** — A slowdown that vanishes at night points to a resource limit, not a code defect.
5. **Look at table sizes** — Connection logs, statistics, abandoned carts and stored searches grow without limit and eventually slow every query.

## The panic-installed cache trap

> Adding a cache module to an already slow site hides the symptom on public pages and leaves the checkout, which is never cached, exactly as slow as before. Caching comes after fixing the cause, not instead of it.

## Carry on with the right page

- **Diagnosing a slow shop** — The full measurement method, before deciding what to optimise. ([/guides/diagnostiquer-boutique-lente](/guides/diagnostiquer-boutique-lente))
- **Slow PrestaShop shop** — If the cause sits in PrestaShop: cache, CCC, category queries. ([/prestashop/boutique-lente](/prestashop/boutique-lente))
- **Slow WordPress or WooCommerce site** — If the cause sits in WordPress: plugins, product queries, admin area. ([/wordpress-woocommerce/site-lent](/wordpress-woocommerce/site-lent))
- **TTFB explained** — The figure that separates a server slowdown from a rendering slowdown. ([/glossaire/ttfb](/glossaire/ttfb))

## FAQ

### My host insists everything is fine on their side. What do I answer?

Ask for your account’s processor and memory usage over the last seven days, plus the number of slow database queries. Those figures always exist, and they settle the question.

### Should I change hosting to fix a slowdown?

Sometimes, but rarely first. A poorly optimised site stays slow on a more powerful machine; it just costs more. I measure where the time goes first.

### Can slowness come from a hacked site?

Yes. A compromised site burns resources sending spam or serving parasite pages. Unexplained slowness with abnormal outbound traffic should be handled as a security incident.

### Why is my site fast for me and slow for customers?

Your browser keeps most of the files in memory. Test in private browsing, over a mobile connection and from another device: that is what your visitors get.

### How long does it take to identify the cause?

Identification is short when server logs are available and the switch date is known. It is the fix that varies, depending on whether it is a setting or a query to rewrite.