Re: BUG #15446: Crash on ALTER TABLE

On 1/5/19 12:09 PM, Andres Freund wrote:
> Hi,
>
> On 2019-01-05 12:11:45 +0000, Dean Rasheed wrote:
>> It looks like the problem was introduced in PG11 by 16828d5c02 (Fast
>> ALTER TABLE ADD COLUMN with a non-NULL default). The first ALTER TABLE
>> adds a new column with a non-null default, setting atthasmissing and
>> attmissingval. Then the second ALTER TABLE changes the type of the new
>> column, but it fails to update attmissingval to match, and thus it
>> falls over when trying to re-open the relation because the value in
>> attmissingval is no longer compatible with the attribute type.
> Paging Dr Dunstan.



Investigating with this test case:


    DROP TABLE IF EXISTS foo;
    CREATE TABLE foo (a int);
    ALTER TABLE foo ADD COLUMN b double precision DEFAULT 0.2;
    ALTER TABLE foo ALTER COLUMN b TYPE varchar(5) USING b::varchar(5);


cheers


andrew

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