Re: Index Skip Scan
| От | Jeff Janes |
|---|---|
| Тема | Re: Index Skip Scan |
| Дата | |
| Msg-id | CAMkU=1x0984uC7PuupnnF6rVeMg6q3OwhU8k906mVZODstaGgQ@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Index Skip Scan (Dmitry Dolgov <9erthalion6@gmail.com>) |
| Список | pgsql-hackers |
On Wed, Feb 20, 2019 at 11:33 AM Dmitry Dolgov <9erthalion6@gmail.com> wrote:
> On Fri, Feb 1, 2019 at 8:24 PM Jesper Pedersen <jesper.pedersen@redhat.com> wrote:
>
> Dmitry and I will look at this and take it into account for the next
> version.
In the meantime, just to not forget, I'm going to post another version with a
fix for cursor fetch backwards, which was crashing before.
This version of the patch can return the wrong answer.
create index on pgbench_accounts (bid, aid);
begin; declare c cursor for select distinct on (bid) bid, aid from pgbench_accounts order by bid, aid;
fetch 2 from c;
bid | aid
-----+---------
1 | 1
2 | 100,001
fetch backward 1 from c;
bid | aid
-----+---------
1 | 100,000
Without the patch, instead of getting a wrong answer, I get an error:
ERROR: cursor can only scan forward
HINT: Declare it with SCROLL option to enable backward scan.
If I add "SCROLL", then I do get the right answer with the patch.
Cheers,
Jeff
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