slow submit order with accounts with long order history
We just updated our Magentox§ shop to 2.4.3-p1 from 2.3.7. Our shop is fast and works fine, except for one thing.
We have newer deleter orders so we have 8-year order history at our DB (about 130 000 orders). We sell quite low costs products and our typical order has many lines (10-30) and big quantities. We have customers that have placed hundreds of orders.
We have noticed long loading times after customers (or we at admin) click "submit order". The problem has just gotten worse over years and after update, it is even worse.
I make some tests and with accounts that had 500 orders "submit order" took 60s. Then I deleted orders 50 by 50 and found out:
500 order - 60s
350 order - 52s
200 orders - 41s
100 orders - 26s
50orders - 19s
zero orders - 3s
I disabled all non-Magento extensions but that did not make any change.
Does Magento write some order statistic when "submit order" has been clicked? Or why does it take so long? I also noticed some higher CPU stat when clicked "submit order" but that is probably normal.
Any way to fix this problem? We CAN delete orders but rather fix it otherwise.