Optimize Workload by Skipping Locked Rows

Use SKIP LOCKED to Process Available Rows

Write a PostgreSQL query to lock rows using SELECT FOR UPDATE with the SKIP LOCKED option to process only unlocked rows.

Solution:

-- Lock available rows in the Orders table, skipping those already locked.
SELECT * FROM Orders -- Specify the table to query.
FOR UPDATE SKIP LOCKED; -- Skip rows that are currently locked.

Explanation:

• Purpose of the Query:
• The goal is to avoid waiting for locks by skipping rows that are currently locked by other transactions.
• This demonstrates how SKIP LOCKED can improve throughput in concurrent processing.
• Key Components:
• FOR UPDATE SKIP LOCKED : Locks rows while skipping those that are already locked.
• The query operates on the Orders table to fetch available rows.
• Real-World Application:
• Often used in job queues or order processing systems to allow multiple workers to process rows without conflict.

Notes:

• Rows skipped due to being locked will not be processed by this query.
• Use SKIP LOCKED when it’s acceptable to process only a subset of rows.

For more Practice: Solve these Related Problems:

• Write a PostgreSQL query to select and lock available rows from the Tasks table using FOR UPDATE SKIP LOCKED.
• Write a PostgreSQL query to fetch pending orders from the Orders table using FOR UPDATE SKIP LOCKED to process only unlocked orders.
• Write a PostgreSQL query to lock rows in the Jobs table using FOR UPDATE SKIP LOCKED where status = 'queued'.
• Write a PostgreSQL query to select records from the Messages table using FOR UPDATE SKIP LOCKED to avoid waiting for locked rows.

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