Hello, @ALG1970
Thank you for your question! It seems you found a bug in the plugin!
The "tp" table is actually a temporary table for document IDs, used only for searching and not used when building the index. Normally this table should not grow, on the contrary, its normal size is 0 records.
This made me think that there might be an error in the code and this table is not cleared in a timely manner. Indeed, the error was found and corrected. I've poured the new version into the Wordpress repository, so I recommend updating now (version 1.59.209).
https://wordpress.org/plugins/fulltext-search/
Immediately after installation, do any search query and the "tp" table should be automatically cleaned up (due to its size, this process may take a long time).
As for the table "vectors", together with the tables "words", "docs" and "index", it represents the search index. All your documents are encoded in these tables in the form of numbers and ratios, and the structure of the tables is such that it allows you to find documents with the specified words in milliseconds, even if the size of the tables is tens of gigabytes. This is the point of indexed search.
So the answer is no. You can't shrink the "vectors" table.
If you are concerned about the database size, I can offer you to disable index optimisation (there is such an option on the main page of the plugin settings).
The index optimiser essentially creates a compressed version of the main index and stores it in the "vc" table, which can also take up a large size.
If you turn off optimisation, the "vc" table will be cleaned up (or you can clean it up manually with the "truncate table wpftsi_vc" query.
Hope this helps.
Please let me know if new WPFTS version solved you problem.
Thank you!