Re: UPDATE sql question
От | Ron Johnson |
---|---|
Тема | Re: UPDATE sql question |
Дата | |
Msg-id | 1059756006.7508.643.camel@haggis обсуждение исходный текст |
Ответ на | Re: UPDATE sql question (Tom Lane <tgl@sss.pgh.pa.us>) |
Список | pgsql-general |
On Fri, 2003-08-01 at 11:15, Tom Lane wrote: > Ron Johnson <ron.l.johnson@cox.net> writes: > >> I'd think that in most cases, the extra time spent checking to see > >> whether the updated columns didn't change would be a net loss. > > > Would it always be a net loss, though? > > You're asking the wrong question. From my perspective, the question > is whether it'd be a net win averaged across all UPDATEs at all > installations everywhere. I can't believe that it would be. > > > CPUs are so fast, nowadays. How many microseconds *would* be spent? > > That's been a standard excuse for bad design for decades now :-(. Very true! How is it bad design to try and save an IO, though? > Yeah, > the comparisons might be cheap (or not, on some datatypes) ... but the > potentially-avoided computation is reduced by a faster CPU as well. But we don't know. MS, IBM or Oracle have the resources to do that kind of analysis. We don't. > If you have a particular application and table where no-op UPDATEs occur > often enough that it's really a win to suppress them, you can put in a > trigger to do it. Or better, fix the application to not issue the > UPDATE in the first place; that saves way more computation for the same > basic comparison overhead. Which is what I also said... <QUOTE> Of course, one could always say, "Hey, application! Don't update unchanged values!!!!". </QUOTE> -- +-----------------------------------------------------------------+ | Ron Johnson, Jr. Home: ron.l.johnson@cox.net | | Jefferson, LA USA | | | | "I'm not a vegetarian because I love animals, I'm a vegetarian | | because I hate vegetables!" | | unknown | +-----------------------------------------------------------------+
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