Horton

Re: An out-of-date comment in nodeIndexonlyscan.c

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Ashwin Agrawal <aagrawal@pivotal.io>, Pg Hackers <pgsql-hackers@postgresql.org>, Heikki Linnakangas <hlinnaka@iki.fi>, Kevin Grittner <kgrittn@gmail.com>
Date: 2021-06-14T02:28:50Z
Lists: pgsql-hackers 
On Mon, 14 Jun 2021 at 10:03, Thomas Munro <thomas.munro@gmail.com> wrote:
>
> On Mon, Jun 14, 2021 at 12:54 AM David Rowley <dgrowleyml@gmail.com> wrote:
> > I think a more optimal and nicer way of doing that would be setting
> > bits in a Bitmapset then checking bms_num_members is equal to
> > n_scan_keys.
>
> Shouldn't it be compared with indnkeyatts?  Yes, much nicer, thanks!

Oh yeah, I did mean that. Thanks for the correction.

Have you also thought about deferrable unique / primary key constraints?

It's possible to the uniqueness temporarily violated during a
transaction when the unique constraint is deferred,

For example:
create table t (id int primary key deferrable initially deferred);
begin;
insert into t values(1),(1);
select * from t;
 id
----
  1
  1
(2 rows)

I think you'd just need to add a check to ensure that indimmediate is
true around where you're checking the indisunique flag.

David

Commits

  1. Block ALTER INDEX/TABLE index_name ALTER COLUMN colname SET (options)

  2. Fix misleading comment in nodeIndexonlyscan.c.

  3. Eliminate xmin from hash tag for predicate locks on heap tuples.

  4. Fix serializable mode with index-only scans.