Re: Dependencies on the system view

On Fri, Sep 20, 2024 at 7:32 AM Olleg <splarv(at)ya(dot)ru> wrote:

> Hi all.
>
> One of our programmer created a view based on the system view. I tried
> to explain him, that he created a dependency from the ordinary database
> to the system object and this is a bad idea. But he is not smart enough.
> So I need a guru opinion. Is this permissible or will here be a trouble
> with, for instance, pg_upgrade?
>
> CREATE OR REPLACE VIEW public.all_tables
> AS SELECT n.nspname AS schemaname,
> c.relname AS tablename,
> pg_get_userbyid(c.relowner) AS tableowner,
> c.reltuples AS num_rows,
> c.relkind,
> CASE c.relkind
> WHEN 'f'::"char" THEN 'Foreign table'::text
> WHEN 'r'::"char" THEN 'Relation'::text
> WHEN 'i'::"char" THEN 'Index'::text
> WHEN 'S'::"char" THEN 'Sequence'::text
> WHEN 't'::"char" THEN 'TOAST'::text
> WHEN 'v'::"char" THEN 'View'::text
> WHEN 'm'::"char" THEN 'Materialized view'::text
> WHEN 'c'::"char" THEN 'Composite type'::text
> WHEN 'p'::"char" THEN 'Partitioned table'::text
> WHEN 'I'::"char" THEN 'partitioned Index'::text
> ELSE NULL::text
> END AS rel_type,
> c.relpersistence,
> CASE c.relpersistence
> WHEN 'p'::"char" THEN 'permanent'::text
> WHEN 'u'::"char" THEN 'unlogged'::text
> WHEN 't'::"char" THEN 'temporary'::text
> WHEN 'c'::"char" THEN 'constant'::text
> ELSE NULL::text
> END AS persistence,
> t.spcname AS tablespace,
> c.relhasindex AS hasindexes,
> c.relhasrules AS hasrules,
> c.relhastriggers AS hastriggers
> FROM pg_class c
> LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
> LEFT JOIN pg_tablespace t ON t.oid = c.reltablespace;
>

1. pg_upgrade will throw an error if a column in one of those catalog
tables is *removed*. Version release notes *should* mention whether
columns are dropped; you'll just have to drop that view beforehand, and
create a new version afterwards, possibly modifying any pg/plsql. No big
deal, honestly; just something to keep in mind.

2. The query will become incomplete/wrong when new relkind and
relpersistence values are added, necessitating an updated version. Again,
not a big deal, and just something to keep in mind.

Thus, I see no problem with that sort of view. Heck, I've made similar
views; they're all over my cron jobs. (I think it should not be in public
-- my views all go in the "dba" schema -- but that's a different issue.)

--
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