Re: 9.5: UPDATE/DELETE .. ORDER BY .. LIMIT ..
| От | Jeff Janes |
|---|---|
| Тема | Re: 9.5: UPDATE/DELETE .. ORDER BY .. LIMIT .. |
| Дата | |
| Msg-id | CAMkU=1zLG7e6-OA1LOcx4B0ahAz834P27Ov6PvR3nAhhbDHjNw@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: 9.5: UPDATE/DELETE .. ORDER BY .. LIMIT .. (Robert Haas <robertmhaas@gmail.com>) |
| Список | pgsql-hackers |
On Wed, May 14, 2014 at 8:26 AM, Robert Haas <robertmhaas@gmail.com> wrote:
On Sun, May 11, 2014 at 12:47 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:I'd say "no". Partitioning is important, and we need to make it more
> Simon Riggs <simon@2ndQuadrant.com> writes:
>> On 11 May 2014 11:18, Andres Freund <andres@2ndquadrant.com> wrote:
>>> I don't know. I'd find UPDATE/DELETE ORDER BY something rather
>>> useful.
>
>> Perhaps if an index exists to provide an ordering that makes it clear
>> what this means, then yes.
>
> The $64 question is whether we'd accept an implementation that fails
> if the target table has children (ie, is partitioned).
seamless and better-integrated, not add new warts.
I think the importance of partitioning argues the other way on this issue. Where I most wanted a LIMIT clause on DELETE is where I was moving tuples from one partition to a different one in a transactional way using bite-size chunks that wouldn't choke the live system with locks or with IO.
So the DELETE was always running against either a child by name, or against ONLY parent, not against the whole inheritance tree. Not being able to do this on single partitions makes partitioning harder, not easier.
Sure, I can select the nth smallest ctid and then "WITH T AS (DELETE FROM ONLY foo WHERE ctid < :that RETURNING *) INSERT INTO bar SELECT * from T", but how annoying.
> That seemsI like this feature, but if I were searching for places where it makes
> to me to not be up to the project's usual quality expectations, but
> maybe if there's enough demand for a partial solution we should do so.
sense to loosen our project's usual quality expectations, this isn't
where I'd start.
In this case I'd much rather have half a loaf rather than none at all. We wouldn't be adding warts to partitioning, but removing warts from the simpler case.
Cheers,
Jeff
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