Prevent "LOCK TABLES" in qa_db_word_mapto_ids_add($words)

[q2apro]

I am still wondering why some of my heavy visited website requests take a while, one of the culprits is the indexing, which I need to accept as necessary. But now I stumbled over https://github.com/q2a/question2answer/blob/dev/qa-include/db/post-create.php#L249

qa_db_query_sub('LOCK TABLES ^words WRITE'); // to prevent two requests adding the same word

From my understanding, the entire db table gets locked until it is unlocked again. So no other queries can take place.

Shouldn't a LOCK be avoided regarding performance issues and other problems?

See also https://stackoverflow.com/q/6621303/1066234

And the LOCK seems also to lock the constraint tables (titlewords, contentwords, tagwords, posttags):

If you lock a table explicitly with LOCK TABLES, any tables related by a foreign key constraint are opened and locked implicitly. For foreign key checks, a shared read-only lock (LOCK TABLES READ) is taken on related tables. For cascading updates, a shared-nothing write lock (LOCK TABLES WRITE) is taken on related tables that are involved in the operation.

https://dev.mysql.com/doc/refman/8.0/en/lock-tables.html

Probably the insert of missing words can be put into one single MYSQL query, see examples at:
https://stackoverflow.com/a/6621549/1066234
https://stackoverflow.com/a/6621547/1066234

INSERT INTO loggingtable (url) SELECT url FROM tablewithurls u LEFT JOIN loggingtable l ON l.url=t.url WHERE {some criterion used to pick the url to work on} AND l.url IS NULL

Probably helpful too: "MySQL: Insert record if not exists in table" https://stackoverflow.com/q/3164505/1066234