Stop Infinite Recursion with a Trigger-Based Solution

Recursive Trigger Prevention using Stored Procedure

Write a PostgreSQL query to create a trigger that calls a stored procedure with a mechanism to prevent recursive calls during updates.

Solution:

-- Create or replace a function named prevent_recursive that returns a trigger
CREATE OR REPLACE FUNCTION prevent_recursive() RETURNS TRIGGER AS $$
BEGIN
    -- Check if the trigger is being called recursively (TG_LEVEL > 1)
    IF TG_LEVEL > 1 THEN
        -- Return the new row without further processing
        RETURN NEW;
    END IF;
    -- Execute update logic only for first-level trigger
    UPDATE some_table SET col = NEW.col WHERE id = NEW.id;
    -- Return the new row
    RETURN NEW;
END;
-- Specify the language used in the function as PL/pgSQL
$$ LANGUAGE plpgsql;
-- Create trigger to invoke the stored procedure on updates in some_table
CREATE TRIGGER trg_prevent_recursive
-- Specify the trigger timing as AFTER UPDATE
AFTER UPDATE ON some_table
-- Define the trigger granularity as FOR EACH ROW
FOR EACH ROW
-- Execute the specified function prevent_recursive() when the trigger is invoked
EXECUTE FUNCTION prevent_recursive();

Explanation:

• Purpose of the Query:
• The goal is to avoid infinite recursive trigger calls during an update operation.
• This demonstrates how to check trigger nesting levels using TG_LEVEL.
• Key Components:
• TG_LEVEL is used to determine the trigger recursion depth.
• The stored procedure contains conditional logic to prevent further execution if recursion is detected.
• Real-World Application:
• Essential in systems where cascading updates might lead to unintended recursive calls and performance issues.

Notes:

• Confirm that the database version supports TG_LEVEL.
• Use caution when performing operations that could trigger additional updates.

For more Practice: Solve these Related Problems:

• Write a PostgreSQL query to create a trigger that prevents recursive calls by setting and checking a session-level flag.
• Write a PostgreSQL query to create a trigger that uses a temporary table marker to avoid recursive trigger executions.
• Write a PostgreSQL query to create a trigger that self-disables during an update operation to prevent infinite recursion.
• Write a PostgreSQL query to create a trigger that compares OLD and NEW values to decide if further trigger recursion is needed.

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Previous PostgreSQL Exercise: Cascade Update Trigger using Stored Procedure.