Re: Difference in execution plans pg12 vs pg14

On 2021-12-11 06:00:40 +0500, Дмитрий Иванов wrote:
> Afternoon. I was able to make the necessary changes to my base needed to
> migrate win_pg12 to debian pg14.
> But there is a new problem, which was not there at the initial stage so I
> checked:
>
> win_pg12:
> ->  Index Scan using index_class_tree_full on class c  (cost=0.28..2.50 rows=1
> width=235) (actual time=0.030..0.032 rows=1 loops=1)
>                      Index Cond: (id = 650)
> debian_pg14:  
> ->  Index Scan using index_class_tree_full on class c  (cost=0.28..2.50 rows=1
> width=235) (actual time=842.795..842.796 rows=1 loops=1)
>                      Index Cond: (id = 650)

Is this repeatable or did it just occur once?

32 µs to retrieve a single row via index probably means that it was
already cached in RAM
842796 µs to retrieve a single row via index doesn't even look realistic
for a completely cold database on a slow rotating hard disk. If this
happened only once I suspect that something else interfered (maybe
another I/O intensive process, if this is on a VM maybe even on another
guest). If it is repeatable, something very weird is going on.

        hp

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