Re: REINDEXdb performance degrading gradually PG13.4

On Tue, May 31, 2022 at 9:12 PM David G. Johnston <
david(dot)g(dot)johnston(at)gmail(dot)com> wrote:

> On Tuesday, May 31, 2022, Praneel Devisetty <devisettypraneel(at)gmail(dot)com>
> wrote:
>
>>
>> Initially it was processing 1000 tables per minute. Performance is
>>> gradually dropping and now after 24 hr it was processing 90 tables per
>>> minute.
>>>
>>
> That seems like a fairly problematic metric given the general vast
> disparities in size tables have.
>
> Building indexes is so IO heavy that the non-IO bottlenecks that exists
> likely have minimal impact on the overall times this rebuild everything
> will take. That said, I’ve never done anything at this scale before. I
> wouldn’t be too surprised if per-session cache effects are coming into play
> given the number of objects involved and the assumption that each session
> used for parallelism is persistent. I’m not sure how the parallelism works
> for managing the work queue though as it isn’t documented and I haven’t
> inspected the source code.
>

could you please share more about per-session cache effects /Point me to
link with more info .