Re: pgsql: Improve handling of inherited GENERATED expressions.

On 2023-01-11 We 15:55, Tom Lane wrote:
> Improve handling of inherited GENERATED expressions.
>
> In both partitioning and traditional inheritance, require child
> columns to be GENERATED if and only if their parent(s) are.
> Formerly we allowed the case of an inherited column being
> GENERATED when its parent isn't, but that results in inconsistent
> behavior: the column can be directly updated through an UPDATE
> on the parent table, leading to it containing a user-supplied
> value that might not match the generation expression. This also
> fixes an oversight that we enforced partition-key-columns-can't-
> be-GENERATED against parent tables, but not against child tables
> that were dynamically attached to them.
>
> Also, remove the restriction that the child's generation expression
> be equivalent to the parent's. In the wake of commit 3f7836ff6,
> there doesn't seem to be any reason that we need that restriction,
> since generation expressions are always computed per-table anyway.
> By removing this, we can also allow a child to merge multiple
> inheritance parents with inconsistent generation expressions, by
> overriding them with its own expression, much as we've long allowed
> for DEFAULT expressions.
>
> Since we're rejecting a case that we used to accept, this doesn't
> seem like a back-patchable change. Given the lack of field
> complaints about the inconsistent behavior, it's likely that no
> one is doing this anyway, but we won't change it in minor releases.

This appears to have caused a problem with cross-version upgrade. It's
not showing on the uploaded buildfarm logs (I will fix that) but the
error from crake is this:

pg_restore: while PROCESSING TOC:

pg_restore: from TOC entry 424; 1259 25257 TABLE gtest_normal_child buildfarm

pg_restore: error: could not execute query: ERROR:  column "b" in child table must not be a generated column

Command was:

-- For binary upgrade, must preserve pg_type oid

SELECT pg_catalog.binary_upgrade_set_next_pg_type_oid('25259'::pg_catalog.oid);

-- For binary upgrade, must preserve pg_type array oid

SELECT pg_catalog.binary_upgrade_set_next_array_pg_type_oid('25258'::pg_catalog.oid);

-- For binary upgrade, must preserve pg_class oids and relfilenodes

SELECT pg_catalog.binary_upgrade_set_next_heap_pg_class_oid('25257'::pg_catalog.oid);

SELECT pg_catalog.binary_upgrade_set_next_heap_relfilenode('25257'::pg_catalog.oid);

CREATE TABLE "public"."gtest_normal_child" (

    "a" integer,

    "b" integer GENERATED ALWAYS AS (("a" * 2)) STORED

);

-- For binary upgrade, set up inheritance this way.

ALTER TABLE ONLY "public"."gtest_normal_child" INHERIT "public"."gtest_normal";

-- For binary upgrade, set heap's relfrozenxid and relminmxid

UPDATE pg_catalog.pg_class

SET relfrozenxid = '6388', relminmxid = '1'

WHERE oid = '"public"."gtest_normal_child"'::pg_catalog.regclass;

cheers

andrew

--
Andrew Dunstan
EDB: https://www.enterprisedb.com