How SELECT statement can cause disk write IO - Query Plan 2

query_plan_2

                                                                         QUERY PLAN                                                                          
-------------------------------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=1038449.15..1038460.82 rows=100 width=206) (actual time=23225.822..26199.674 rows=100 loops=1)
   Buffers: shared hit=9749 read=201159, temp read=182633 written=195896
   ->  Gather Merge  (cost=1038449.15..2983029.28 rows=16666666 width=206) (actual time=23225.820..26199.659 rows=100 loops=1)
         Workers Planned: 2
         Workers Launched: 2
         Buffers: shared hit=9749 read=201159, temp read=182633 written=195896
         ->  Sort  (cost=1037449.13..1058282.46 rows=8333333 width=206) (actual time=23219.185..23219.219 rows=75 loops=3)
               Sort Key: book.title, book.id
               Sort Method: top-N heapsort  Memory: 42kB
               Worker 0:  Sort Method: top-N heapsort  Memory: 42kB
               Worker 1:  Sort Method: top-N heapsort  Memory: 41kB
               Buffers: shared hit=9749 read=201159, temp read=182633 written=195896
               ->  Parallel Hash Join  (cost=255098.79..718955.14 rows=8333333 width=206) (actual time=16346.933..21339.523 rows=6666667 loops=3)
                     Hash Cond: (book.author_id = author.id)
                     Buffers: shared hit=9679 read=201159, temp read=182633 written=195896
                     ->  Parallel Seq Scan on book  (cost=0.00..230392.33 rows=8333333 width=30) (actual time=0.986..6066.543 rows=6666667 loops=3)
                           Buffers: shared hit=870 read=146189
                     ->  Parallel Hash  (cost=105361.13..105361.13 rows=4166613 width=168) (actual time=5283.160..5283.161 rows=3333333 loops=3)
                           Buckets: 32768  Batches: 1024  Memory Usage: 832kB
                           Buffers: shared hit=8725 read=54970, temp written=61372
                           ->  Parallel Seq Scan on author  (cost=0.00..105361.13 rows=4166613 width=168) (actual time=0.029..2729.765 rows=3333333 loops=3)
                                 Buffers: shared hit=8725 read=54970
 Planning Time: 8.556 ms
 Execution Time: 26199.972 ms
(24 rows)