Re: Atomic operations?

On 18-Mar-08, at 11:05 AM, Paul Tomblin wrote:

> On Tue, Mar 18, 2008 at 10:17 AM, Dave Cramer <pg(at)fastcrypt(dot)com>
> wrote:
>>>> On 18-Mar-08, at 9:40 AM, Paul Tomblin wrote:
>>>>> I'm doing a simple delete/insert on a table, rather than trying to
>>>>> figure out whether the row exists or not and then doing an
>>>>> update or
>>>>> an insert. But what I'm discovering is that every now and then I
>
>>>> Can't you just check the return value from the delete to see if
>>>> anything was deleted ?
>>>
>>> I'm not sure how that would help. If I do the delete and it didn't
>>> delete anything, that doesn't tell me if some other process inserted
>>> it in the meantime.
>>>
>> which ever process succeeds in deleting should do the insert.
>
> Doesn't help in the case where the record wasn't in there in the
> first place.
>

What you are looking for is upsert. It's on the todo list http://www.postgresql.org/docs/faqs.TODO.html

In the meantime you can lock the table or create a function to do a
select and update or insert.

Dave
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