Re: Proposal: Global Index

On Thu, Oct 31, 2019 at 03:02:40PM -0400, Isaac Morland wrote:
>On Thu, 31 Oct 2019 at 14:50, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
>
>> Greetings,
>>
>> * Peter Geoghegan (pg(at)bowt(dot)ie) wrote:
>>
>[....]
>
>>
>> Absolutely- our lack of such is a common point of issue when folks are
>> considering using or migrating to PostgreSQL.
>>
>
>Not sure how similar my situation really is, but I find myself wanting to
>have indices that cross non-partition members of an inheritance hierarchy:
>
>create table t (
> id int,
> primary key (id)
>);
>
>create table t1 (
> a text
>) inherits (t);
>
>create table t2 (
> b int,
> c int
>) inherits (t);
>
>So "t"s are identified by an integer; and one kind of "t" has a single text
>attribute while a different kind of "t" has 2 int attributes. The idea is
>that there is a single primary key constraint on the whole hierarchy that
>ensures only one record with a particular id can exist in all the tables
>together. I can imagine wanting to do this with other unique constraints
>also.
>

IMO the chances of us supporting global indexes with generic inheritance
hierarchies are about zero. We don't even support creating "partition"
indexes on those hierarchies ...

>At present I don't actually use inheritance; instead I put triggers on the
>child tables that do an insert on the parent table, which has the effect of
>enforcing the uniqueness I want.

Does it? Are you sure it actually works in READ COMMITTED? What exactly
does the trigger do?

regards

--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services