log.txt

bt2=# SET enable_seqscan = off;
SET
bt2=# explain(analyze, buffers) select distinct serial_number from telemetry;
                                                                            QUERY PLAN                                                                             
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Unique  (cost=0.56..29452499.56 rows=608 width=4) (actual time=1.886..75483.005 rows=874 loops=1)
   Buffers: shared hit=68873 read=884486 dirtied=56
   ->  Index Only Scan using concurently on telemetry  (cost=0.56..29347579.02 rows=41968215 width=4) (actual          Buffers: shared hit=68873 read=884486 dirtied=56
time=1.884..71989.949 rows=42559723 loops=1)
         Heap Fetches: 9134141
 Planning Time: 0.280 ms
 Execution Time: 75485.129 ms
(7 rows)

bt2=# SET enable_seqscan = on;
SET
bt2=# explain(analyze, buffers) select distinct serial_number from telemetry;
                                                               QUERY PLAN                                                                
-----------------------------------------------------------------------------------------------------------------------------------------
 HashAggregate  (cost=2962701.69..2962707.77 rows=608 width=4) (actual time=55724.390..55724.523 rows=874 loops=1)
   Group Key: serial_number
   Buffers: shared hit=106176 read=2331923
   ->  Seq Scan on telemetry  (cost=0.00..2857781.15 rows=41968215 width=4) (actual time=0.011..18983.038 rows=42559723 loops=1)
         Buffers: shared hit=106176 read=2331923
 Planning Time: 0.149 ms
 Execution Time: 55724.690 ms
(7 rows)