Can Concurrent `SELECT` and `INSERT` Operations in PL/pgSQL Lead to Race Conditions?

Are

function-based SELECT or INSERT operations prone to race conditions?

In your PL/pgSQL function you insert data into the Posts table and loop through the tags to insert it into the Tags and Taggings tables. You are concerned that this process may encounter a race condition when multiple users try to delete tags and create posts at the same time.

Under concurrent write load, the concept of "SELECT or INSERT" arises when trying to insert a new row into a table, but want to retrieve the row when it already exists. In SQL, this can be achieved using the INSERT ... ON CONFLICT ... DO SOMETHING statement.

Avoid race conditions

Your function uses this technique when inserting tags into the Tags table, but you may encounter a race condition if another transaction deletes the associated tag before your transaction commits. To prevent this, consider the following techniques:

• UPSERT function : Create a function that handles the insertion and selection operations of tags. This function should use a loop to repeatedly try to insert and select tags until successful.
• Lock: In a SELECT statement within a function, use FOR SHARE to lock existing rows to ensure that other transactions cannot modify them while your transaction is in progress.

Or, consider...

• LIMITUNION ALL with : Use a UNION ALL query to combine the SELECT and INSERT statements, using the LIMIT 1 clause on the result. This technique allows for a quick exit if the row already exists or if the insertion was successful.
• Separate INSERTFunction: Outsource the insertion operation into a separate function. This function should handle any necessary exception handling, while the main function focuses on the overall logic.

By implementing one of these methods, you can prevent race conditions in your functions and ensure data integrity in the database.

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