Hi,
Thanks a lot for your answer and to reassuring me.
At the moment I'm focusing on the home page:
With cache disabled I have 400 queries (without: 268 but maybe with problems).
I think I can gain some performance if I can cache only certain parts.
I'm thinking about how to set this up.
But even if I manage to save the execution of half of the requests (and less files to load): I don't see how I can gain more performance than a page that would load twice as fast and that won't be enough.
Because at the moment there is no problem, so the page is displayed in less than 1 second (or around 1.5 seconds), but there are times when the same page takes more than 5 or 10 seconds (sometimes more).
My host tells me that the hosting server has no problem, that it is not overloaded and that the site should be optimised.
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For me, the main problem (TTFB slow) can also come from the server. (And if not, the problem would be present more regularly in my opinion.)
What I find strange is that the same site with the same host, but on a different server (different hosting), I didn't have as many problems.
The main difference is maybe that there are obviously more visitors than on the test sites, or a underperforming server.
And when the site slows down, the SQL queries I do manually are >100 times slower.
For me, the MySQL server is slowing down.
That's why I'm trying to find solutions to reduce my number of queries.