Обсуждение: View consistency

Hello!

Im using several views for the Usermanagment of a database.
My question is:

How does postgres keep the views consistent to the according tables( if
the original table has been changed)?

Is there a Rule? and how is the Rule invoked. With ON DELETE UPDATE
INSERT of the original table?
I didnt found any Rule in pg_rules.
There should be a rule, because I cannot imagine another way wich tells
the view that the table has been changed.

The problem is: If updating the view takes too much time after every
little manipulation, I couldnt use views for usermanagement because of
performance problems.
Any hints and facts?

Thanks in advance

David

"David M. Richter" <d.richter@dkfz.de> writes:
> How does postgres keep the views consistent to the according tables( if
> the original table has been changed)?

It doesn't have to; views are not materialized in Postgres.  A view
is just a rewrite rule, or macro.
        regards, tom lane

On Thu, 1 Nov 2001, David M. Richter wrote:

> Hello!
>
> Im using several views for the Usermanagment of a database.
> My question is:
>
> How does postgres keep the views consistent to the according tables( if
> the original table has been changed)?

AFAIK it's a select rule on the view that rewrites into the view
expression.  Nothing keeps it consistent because it's effectively just
a macro for the view expression.

"David M. Richter" <d.richter@dkfz-heidelberg.de> writes:
> Select name from patient_view;
> is in reality:
> Select name from (select ...,...,... from basic where xxx=yyy);
> Is that right?

Yup.  The rule rewriter just substitutes the view definition as a
subselect.
        regards, tom lane

Hi,

So every time when I 'll use the view, the constraint over the basic
table will be revalidated.

Select name from patient_view;

is in reality:

Select name from (select ...,...,... from basic where xxx=yyy);

Is that right?

DAvid

Hi,

Thanks, but what I am concerning  is the performance.
In my database are some tables bigger than 6 Millions of rows. If one
row has been changed in the normal table,
so the rule will be invoked and the view will be kept in consistance.
But this will take some time, isn't it?
I cannot simulate that case with my database, because Im still
developing.
So i have to know:

Where is the rule or the macro stored? How could I disable it?

Perhaps I could do a reinit of the view not after any Select, but after
any transaction.
But I dont know that rule or macro!

How can I get some information about the rule (wich was automatically
generated by creating the view)?
Thanks for Your hints

DAvid

---------------------------------------------------------------
"David M. Richter" <d.richter@dkfz.de> writes:
> How does postgres keep the views consistent to the according tables( if
> the original table has been changed)?

It doesn't have to; views are not materialized in Postgres.  A view
is just a rewrite rule, or macro.

                        regards, tom lane