Re: index prefetching

On Thu Aug 14, 2025 at 3:15 PM EDT, Peter Geoghegan wrote:
> On Thu, Aug 14, 2025 at 2:53 PM Andres Freund <andres@anarazel.de> wrote:
>> I think this is just an indicator of being IO bound.
>
> Then why does the exact same pair of runs show "I/O Timings: shared
> read=194.629" for the sequential table backwards scan (with total
> execution time 1132.360 ms), versus "I/O Timings: shared read=352.88"
> (with total execution time 697.681 ms) for the random table backwards
> scan?

Is there any particular significance to the invalid op reports I also see in
the same log files?

 $ cat sequential.txt | grep invalid | head
 2025-08-14 14:35:03.278 EDT [2516983][client backend] [[unknown]][0/1:0] DEBUG:  00000: io 0         |op
invalid|targetinvalid|state IDLE            : wait_one io_gen: 2, ref_gen: 1, cycle 1 
 2025-08-14 14:35:03.278 EDT [2516983][client backend] [[unknown]][0/1:0] DEBUG:  00000: io 0         |op
invalid|targetinvalid|state IDLE            : wait_one io_gen: 3, ref_gen: 2, cycle 1 
 2025-08-14 14:35:03.278 EDT [2516983][client backend] [[unknown]][0/1:0] DEBUG:  00000: io 0         |op
invalid|targetinvalid|state IDLE            : wait_one io_gen: 4, ref_gen: 3, cycle 1 
 2025-08-14 14:35:03.278 EDT [2516983][client backend] [[unknown]][0/1:0] DEBUG:  00000: io 0         |op
invalid|targetinvalid|state IDLE            : wait_one io_gen: 5, ref_gen: 4, cycle 1 
 2025-08-14 14:35:03.278 EDT [2516983][client backend] [[unknown]][0/1:0] DEBUG:  00000: io 0         |op
invalid|targetinvalid|state IDLE            : wait_one io_gen: 6, ref_gen: 5, cycle 1 
 2025-08-14 14:35:03.278 EDT [2516983][client backend] [[unknown]][0/1:0] DEBUG:  00000: io 0         |op
invalid|targetinvalid|state IDLE            : wait_one io_gen: 7, ref_gen: 6, cycle 1 
 2025-08-14 14:35:03.279 EDT [2516983][client backend] [[unknown]][0/1:0] DEBUG:  00000: io 0         |op
invalid|targetinvalid|state IDLE            : wait_one io_gen: 8, ref_gen: 7, cycle 1 
 2025-08-14 14:35:03.279 EDT [2516983][client backend] [[unknown]][0/1:0] DEBUG:  00000: io 0         |op
invalid|targetinvalid|state IDLE            : wait_one io_gen: 9, ref_gen: 8, cycle 1 
 2025-08-14 14:35:03.279 EDT [2516983][client backend] [[unknown]][0/1:0] DEBUG:  00000: io 0         |op
invalid|targetinvalid|state IDLE            : wait_one io_gen: 10, ref_gen: 9, cycle 1 
 2025-08-14 14:35:03.279 EDT [2516983][client backend] [[unknown]][0/1:0] DEBUG:  00000: io 0         |op
invalid|targetinvalid|state IDLE            : wait_one io_gen: 11, ref_gen: 10, cycle 1 
 $ cat sequential.txt | grep invalid | wc -l
5733
 $ cat random.txt | grep invalid | wc -l
2206

--
Peter Geoghegan