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Re: About inheritance

From: Ioannis Theoharis <theohari(at)ics(dot)forth(dot)gr>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: About inheritance
Date: 2004-08-28 22:23:07
Message-ID: Pine.GSO.4.58.0408290111530.11210@ourania.ics.forth.gr (view raw or flat)
Thread:
Lists: pgsql-general

Thanks.

Time is little but visible affected for big chierarhies.


Let me do an other question.

I have again a Root table and a hierarchie of tables, all created with the
inherits relationship like:

create table father(att0 int4);
create table child1() inherits(father);
create table child2() inherits(father);
create table child11() inherits(child1);
create table child12() inherits(child1);
create table child21() inherits(child2);
create table child22() inherits(child2);



First i insert 1000 tuples into father table, and then i delete them and i
insert them into child22

I expekt explain analyze to give the same response time at both cases. But
i found that time increases as where as the level, where data are located,
increases.

Can anybody explain me the reason?





On Sun, 22 Aug 2004, Tom Lane wrote:

> Ioannis Theoharis <theohari(at)ics(dot)forth(dot)gr> writes:
> > I expekt to find the same plans because in both cases there is a union to
> > be done, but i see that in second case there is an additional call to a
> > routine. I meen the 'Subquery Scan "*SELECT* X"'
>
> The subquery scan step is in there because in a UNION construct, there
> may be a need to do transformations on the data before it can be
> unioned.  For instance you are allowed to UNION an int4 and an int8
> column, in which case the int4 values have to be promoted to int8 after
> they come out of the subplan.
>
> In the particular case you are showing, the subquery scan steps aren't
> really doing anything, but AFAIR the planner does not bother to optimize
> them out.  I'd be pretty surprised if they chew up any meaningful amount
> of runtime.
>
> 			regards, tom lane
>
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Subject: Re: About inheritance
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