Postgresql update without lock

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PostgreSQL Update Without Lock

When updating data in PostgreSQL, the default behavior is to acquire a lock on the affected rows to ensure data consistency. However, there are scenarios where you may want to perform an update without locking the rows, such as reducing contention or improving performance in high-concurrency environments.

To achieve this, you can make use of the pg_sleep() function along with subqueries to perform an update without locking the rows. The pg_sleep() function allows you to introduce a delay in the execution of a query.

Here’s an example to demonstrate how to update without locking:

    
      -- Suppose you have a table called "employees" with columns "id" and "salary"
      -- We want to update the salary of employee with id 1 to 50000 without locking other rows

      UPDATE employees
      SET salary = 50000
      WHERE id = 1
      AND NOT EXISTS (
        SELECT 1
        FROM employees
        WHERE id = 1
        FOR UPDATE SKIP LOCKED -- The SKIP LOCKED clause skips locked rows during the update
      );

In the above example, we first attempt to update the salary of the employee with id 1 to 50000. The NOT EXISTS subquery with FOR UPDATE SKIP LOCKED clause ensures that the rows are not locked. By skipping locked rows, other transactions can still read and update them concurrently.

Keep in mind that updating without locks may introduce the risk of concurrent modifications and inconsistent reads. It is important to carefully consider the implications and requirements of your specific use case before deciding to update without locks.

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