Why did the server response time (TTFB) increase after updating PHP to 7.4?

Question

1C-Bitrix

There is a dedicated VPS (4 GB RAM, 60 GB SSD, Dual-core CPU) with Bitrix environment (v.7.5.0) installed.
CMS version: 1C-Bitrix: Site Management 20.0.1800 I

recently updated PHP from 7.2 to 7.4, as a result of which the server began to respond slowly - it takes about 2-3 seconds to TTFB according to the results of synthetic tests (see screenshots).
I checked OPCache and Memcached - no problems were found, caching is working properly.




Tell me, what else can be the reason for such a long server response?

Answer 1

Tell me, what else can be the reason for such a long server response?

Anything, so you need to test normally:
1) Check how quickly the static is given, for example, any jpeg.
2) Check if there are any glitches in the server-puff connection, for example, it is stupid to put echo 1 in the index; exit();, see the time.
3) item 2, but already deeper in the code, somewhere in the area of ​​​​requests in the database
4) Repeat until the problem is clarified.
5) Profit!