Using a database table as a queue

Question

I want to use a database table as a queue. I want to insert in it and take elements from it in the inserted order (FIFO). My main consideration is performance because I have

Answer 1

I had the same general question of "how do I turn a table into a queue" and couldn't find the answer I wanted anywhere.

Here is what I came up with for Node/SQLite/better-sqlite3. Basically just modify the inner WHERE and ORDER BY clauses for your use case.

module.exports.pickBatchInstructions = (db, batchSize) => {
  const buf = crypto.randomBytes(8); // Create a unique batch identifier

  const q_pickBatch = `
    UPDATE
      instructions
    SET
      status = '${status.INSTRUCTION_INPROGRESS}',  
      run_id = '${buf.toString("hex")}',
      mdate = datetime(datetime(), 'localtime')
    WHERE
      id IN (SELECT id 
        FROM instructions 
        WHERE 
          status is not '${status.INSTRUCTION_COMPLETE}'
          and run_id is null
        ORDER BY
          length(targetpath), id
        LIMIT ${batchSize});
  `;
  db.run(q_pickBatch); // Change the status and set the run id

  const q_getInstructions = `
    SELECT
      *
    FROM
      instructions
    WHERE
      run_id = '${buf.toString("hex")}'
  `;
  const rows = db.all(q_getInstructions); // Get all rows with this batch id

  return rows;
};