Oleg, this idea doesn't seem destine for greatness, so it might be worth adding that you can avoid the general case problem of incorrectly- specified-but-long-running query by using statement_timeout...
On Wed, 2005-03-09 at 22:38 +1100, Neil Conway wrote: > Simon Riggs wrote: > > Oleg is saying that the optimizer doesn't protect against foolish SQL > > requests. His query is an example of a foolishly written query. > > IMHO calling this a "foolishly written query" is completely arbitrary. Well, in this case "foolish" is defined by the person that wrote the query, as an expression of regret. > I > can imagine plenty of applications for which a cartesian join makes > sense. Yes, which is why I discussed using a GUC, set only by those people who want to be protected *from themselves*. It's a safety harness that you could choose to put on if you wished. > In this case the user didn't write the query they meant to write > -- but it is surely hopeless to prevent that in the general case :) > > > It seems a reasonable that there might be a GUC such as > > enable_cartesian = on (by default) > > I think the bar for adding a new GUC ought to be significantly higher > than that. Well, the point is moot until somebody writes the rest of the code anyhow. So, add it to the ideas shelf... > In any case, when this problem does occur, it is obvious to the user > that something is wrong, and no harm is done. Given a complex SQL query, > it might take a bit of examination to determine which join clause is > missing -- but the proper way to fix that is better query visualization > tools (perhaps similar RH's Visual Explain, for example). This would > solve the general problem: "the user didn't write the query they > intended to write", rather than a very narrow subset ("the user forgot a > join clause and accidentally computed a cartesian product"). This issue only occurs when using SQL as the user interface language, which is common when using a database in iterative or exploratory mode e.g. Data Warehousing. If you are using more advanced BI tools then they seldom get the SQL wrong. This is not useful in a situation where people are writing SQL for a more static application. Best Regards, Simon Riggs ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq