Re: [pgsql-hackers] Daily digest v1.10705 (13 messages)

On Thu, 2010-06-03 at 05:53 -0300, pgsql-hackers-owner@postgresql.org
wrote:
> [ . . . ]
>
> In my current idea, when a qual-node that contains FuncExpr tries to
> reference a part of relations within a security view, its referencing
> relations will be expanded to whole of the security view at
> distribute_qual_to_rels().
> [ . . . ]

I may be missing something here but this seems a bit too simplistic and,
I think, fails to deal with an important use case.

Security views, that do anything useful at all, tend to introduce
performance issues.  I am concerned that placing a conceptual barrier
between the secured and unsecured parts of queries is going to
unnecessarily restrict what the optimiser can do.

For example consider that we have three secured views, each of the form:
 create view s_x as select * from x where i_can_see(x.key);

and consider the query:
 select stuff from s_x    inner join s_y on s_y.key = s_x.key   inner join s_z on s_z.key = s_x.key   where fn(s_x.a) =
3;

The optimiser ought to be able to spot the fact that i_can_see() need
only be called once for each joined result.  By placing a barrier (if I
understand your proposal correctly) between the outermost joins and the
inner views, doesn't this optimisation become impossible?

I think a simpler solution may be possible here.  If you can tag the
function i_can_see() as a security function, at least in the context of
its use in the security views, and then create the rule that security
functions are always considered to be lower cost than user-defined
non-security functions, don't we achieve the result of preventing the
insecure function from seeing rows that it shouldn't?

I guess my concern is that a query may be constructed a=out of secured
and unsecured parts and the optimiser should be free to group all of the
secured parts together before considering the unsecured parts.

Sorry for the imprecise language and terminolgy, and also if I have
completely misunderstood the implications.

Best Wishes

__
Marc (the veil guy)