A15: regressed anti-join, index-only
  master                         (min):       9.041 ms (avg=9.134, max=9.262)
  patch + yield    (prefetch=on) (min):       8.429 ms (avg=8.520, max=8.636) [0.932x vs master]
  patch + no yield (prefetch=on) (min):      10.225 ms (avg=10.323, max=10.394) [1.131x vs master]

  Query:
    SELECT o.customer_id, o.order_date
    FROM prefetch_orders o
    WHERE o.order_date BETWEEN '2023-02-09' AND '2023-02-23'
    AND o.customer_id BETWEEN 36307 AND 37126
    AND NOT EXISTS (
    SELECT 1 FROM prefetch_customers c
    WHERE c.customer_id = o.customer_id
    AND c.region_id = 4
    )
    ORDER BY o.order_date

  master EXPLAIN ANALYZE:
    Sort (actual rows=7882.00 loops=1)
      Sort Key: o.order_date
      Sort Method: quicksort  Memory: 377kB
      Buffers: shared hit=11732 read=237
      I/O Timings: shared read=1.145
      ->  Merge Anti Join (actual rows=7882.00 loops=1)
            Merge Cond: (o.customer_id = c.customer_id)
            Buffers: shared hit=11732 read=237
            I/O Timings: shared read=1.145
            ->  Index Only Scan using prefetch_orders_cust_date_idx on prefetch_orders o (actual rows=8445.00 loops=1)
                  Index Cond: ((customer_id >= 36307) AND (customer_id <= 37126) AND (order_date >= '2023-02-09'::date) AND (order_date <= '2023-02-23'::date))
                  Heap Fetches: 0
                  Index Searches: 772
                  Buffers: shared hit=11629
            ->  Index Scan using prefetch_customers_pkey on prefetch_customers c (actual rows=1858.00 loops=1)
                  Filter: (region_id = 4)
                  Rows Removed by Filter: 35285
                  Index Searches: 1
                  Buffers: shared hit=103 read=237
                  I/O Timings: shared read=1.145
    Planning:
      Buffers: shared hit=16
    Planning Time: 0.155 ms
    Serialization: output=193kB  format=text
    Execution Time: 9.041 ms

  patch + yield (prefetch=on) EXPLAIN ANALYZE:
    Sort (actual rows=7882.00 loops=1)
      Sort Key: o.order_date
      Sort Method: quicksort  Memory: 377kB
      Buffers: shared hit=11732 read=237
      I/O Timings: shared read=0.825
      ->  Merge Anti Join (actual rows=7882.00 loops=1)
            Merge Cond: (o.customer_id = c.customer_id)
            Buffers: shared hit=11732 read=237
            I/O Timings: shared read=0.825
            ->  Index Only Scan using prefetch_orders_cust_date_idx on prefetch_orders o (actual rows=8445.00 loops=1)
                  Index Cond: ((customer_id >= 36307) AND (customer_id <= 37126) AND (order_date >= '2023-02-09'::date) AND (order_date <= '2023-02-23'::date))
                  Heap Fetches: 0
                  Index Searches: 772
                  Buffers: shared hit=11629
            ->  Index Scan using prefetch_customers_pkey on prefetch_customers c (actual rows=1858.00 loops=1)
                  Filter: (region_id = 4)
                  Rows Removed by Filter: 35285
                  Index Searches: 1
                  Buffers: shared hit=103 read=237
                  I/O Timings: shared read=0.825
    Planning:
      Buffers: shared hit=16
    Planning Time: 0.166 ms
    Serialization: output=193kB  format=text
    Execution Time: 8.429 ms

  patch + no yield (prefetch=on) EXPLAIN ANALYZE:
    Sort (actual rows=7882.00 loops=1)
      Sort Key: o.order_date
      Sort Method: quicksort  Memory: 377kB
      Buffers: shared hit=11795 read=385
      I/O Timings: shared read=1.517
      ->  Merge Anti Join (actual rows=7882.00 loops=1)
            Merge Cond: (o.customer_id = c.customer_id)
            Buffers: shared hit=11795 read=385
            I/O Timings: shared read=1.517
            ->  Index Only Scan using prefetch_orders_cust_date_idx on prefetch_orders o (actual rows=8445.00 loops=1)
                  Index Cond: ((customer_id >= 36307) AND (customer_id <= 37126) AND (order_date >= '2023-02-09'::date) AND (order_date <= '2023-02-23'::date))
                  Heap Fetches: 0
                  Index Searches: 772
                  Buffers: shared hit=11629
            ->  Index Scan using prefetch_customers_pkey on prefetch_customers c (actual rows=1858.00 loops=1)
                  Filter: (region_id = 4)
                  Rows Removed by Filter: 35285
                  Index Searches: 1
                  Buffers: shared hit=166 read=385
                  I/O Timings: shared read=1.517
    Planning:
      Buffers: shared hit=16
    Planning Time: 0.149 ms
    Serialization: output=193kB  format=text
    Execution Time: 10.225 ms