From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
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To: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Expression indexes and dependecies |
Date: | 2013-07-22 21:04:06 |
Message-ID: | 20130722210405.GF3795@eldon.alvh.no-ip.org |
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Lists: | pgsql-hackers |
Pavan Deolasee escribió:
> Hello,
>
> While doing some tests, I observed that expression indexes can malfunction
> if the underlying expression changes.
[...]
> Perhaps this is a known behaviour/limitation, but I could not find that in
> the documentation. But I wonder if it makes sense to check for dependencies
> during function alteration and complain. Or there are other reasons why we
> can't do that and its a much larger problem than what I'm imagining ?
This is a tough problem. The dependency mechanism has no way to keep
track of this kind of dependency; all it does is prevent the function
from being dropped altogether, but preventing it from acquiring a
conflicting definition is outside its charter.
One way to attack this would be registering dependencies of a new kind
on functions used by index expressions. Then CREATE OR REPLACE function
could reject alteration for such functions. I don't know if we care
enough about this case.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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