Magento uses MySQL’s fulltext for search. From time to time when your store has many search request MySQL can have many queries like:
INSERT INTO search_tmp...
Why it happens?
It happens when your store has many catalogsearch request.
How to fix this INSERT INTO search_tmp issue?
Will be fixed since Magento 2.3.4.
The best fix for the following issue is not to use MySQL for catalogsearch. We strongly recommend using Elasticsearch or Sphinx for the catalogsearch on Magento. If you don’t want to switch search Engine you can try to rate limit your catalogsearch requests.