Re: Execution plan changed after upgrade from 7.3.9 to 8.2.3

Thanks for the update.

The following did not change anything in the execution plan

ALTER TABLE lm05_t_tarif_panneau ALTER COLUMN lrg_min SET STATISTICS 1000
ALTER TABLE lm05_t_tarif_panneau ALTER COLUMN lrg_max SET STATISTICS 1000
ANALYZE lm05_t_tarif_panneau

I was able to improve response time by creating indexes, but I would
like to avoid changing the database structure because it is not
maintained by ourseleves, but by the third party vendor.

Richard Huxton wrote:
> vincent(dot)moreau(at)leroymerlin(dot)fr wrote:
>> I have attached the requested information.
>>
>> You will see that the query is quite messy and could be easily improved.
>> Unfortunately, it came from a third party application and we do not
>> have access to the source code.
>
> -> Hash Join (cost=6.31..3056.17 rows=116 width=47) (actual
> time=60.055..70.078 rows=48 loops=280)
> Hash Cond: (g.cod_modele = a.cod_modele)
> -> Seq Scan on lm05_t_tarif_panneau g (cost=0.00..2977.08
> rows=19097 width=43) (actual time=0.008..67.670 rows=4062 loops=280)
>
> It does seem to be running that sequential scan 280 times, which is a
> strange choice to say the least.
>
> Obvious thing #1 is to look at I'd say is the stats on lrg_min,lrg_max
> - try something like:
> ALTER TABLE lm05_t_tarif_panneau ALTER COLUMN lrg_min SET STATISTICS <n>
> You can set <n> up to 1000 (and then the same for lrg_max of course).
> Analyse the table again and see if that gives it a clue.
>
> Second thing might be to try indexes on lrg_min and lrg_max and see if
> the bitmap code in 8.2 helps things.
>
> Very strange plan.

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