Re: UNION ALL vs INHERITANCE

От: Tom Lane
Тема: Re: UNION ALL vs INHERITANCE
Дата: ,
Msg-id: 1869.1103235194@sss.pgh.pa.us
(см: обсуждение, исходный текст)
Ответ на: UNION ALL vs INHERITANCE  (Adi Alurkar)
Список: pgsql-performance

Adi Alurkar <> writes:
> Why does the append resulting from a inheritance take longer than one
> resulting from  UNION ALL?

The index scan is where the time difference is:

>                       ->  Index Scan using fftiallbgrgfid_1102715649 on
> f_f_all_base  (cost=0.00..3.52 rows=1 width=51) (actual
> time=3.871..244.356 rows=28 loops=1)
>                             Index Cond: (group_id = 78745)
>                             Filter: (all_tidx @@ '\'mmcach\''::tsquery)

>                       ->  Index Scan using fftiallbgrgfid_1102715649 on
> f_f_all_base  (cost=0.00..3.52 rows=1 width=51) (actual
> time=3.714..79.996 rows=28 loops=1)
>                             Index Cond: (group_id = 78745)
>                             Filter: (all_tidx @@ '\'mmcach\''::tsquery)

One would have to suppose this is a caching effect, ie, the data is
already in RAM on the second try and doesn't have to be read from disk
again.

            regards, tom lane


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