Re: fast default vs triggers

On 09/18/2018 03:36 PM, Andrew Dunstan wrote:
>
>
> Tomas Vondra has pointed out to me that there's an issue with triggers
> not getting expanded tuples for columns with fast defaults. Here is an
> example that shows the issue:
>
>
>    andrew=# create table blurfl (id int);
>    CREATE TABLE
>    andrew=# insert into blurfl select x from generate_series(1,5) x;
>    INSERT 0 5
>    andrew=# alter table blurfl add column x int default 100;
>    ALTER TABLE
>    andrew=# create or replace function showmej() returns trigger
>    language plpgsql as $$ declare j json; begin j := to_json(old);
>    raise notice 'old x: %', j->>'x'; return new; end; $$;
>    CREATE FUNCTION
>    andrew=# create trigger show_x before update on blurfl for each row
>    execute procedure showmej();
>    CREATE TRIGGER
>    andrew=# update blurfl set id = id where id = 1;
>    NOTICE:  old x: <NULL>
>    UPDATE 1
>    andrew=# update blurfl set id = id where id = 1;
>    NOTICE:  old x: 100
>    UPDATE 1
>    andrew=#
>
>
> The error is fixed with this patch:
>
>
>    diff --git a/src/backend/commands/trigger.c
> b/src/backend/commands/trigger.c
>    index 2436692..f34a72a 100644
>    --- a/src/backend/commands/trigger.c
>    +++ b/src/backend/commands/trigger.c
>    @@ -3396,7 +3396,11 @@ ltrmark:;
>             LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
>         }
>         -   result = heap_copytuple(&tuple);
>    +   if (HeapTupleHeaderGetNatts(tuple.t_data) <
> relation->rd_att->natts)
>    +       result = heap_expand_tuple(&tuple, relation->rd_att);
>    +   else
>    +       result = heap_copytuple(&tuple);
>    +
>         ReleaseBuffer(buffer);
>              return result;
>
> I'm going to re-check the various places that this might have been
> missed. I guess it belongs on the open items list.
>
>
>

I haven't found anything further that is misbehaving. I paid particular
attention to indexes and index-only scans.

I propose to commit this along with an appropriate regression test.

cheers

andrew

--
Andrew Dunstan https://www.2ndQuadrant.com
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