Re: Does PostgreSQL check database integrity at startup?

[Stephen Frost <sfrost@xxxxxxxxxxx>]

Greetings,

* Melvin Davidson (melvin6925@xxxxxxxxx) wrote:
> My query works as designed and has done so
> for two years. It shows the filenames for schemas and tables in the
> database.

I'm glad to hear that it works in your specific use-case.
Unfortunately, it doesn't work in the general case and therefore isn't a
good example.  A proper query to return the filename for each user table
in the current database is:

SELECT
  quote_ident(nsp.nspname) || '.' || quote_ident(c.relname),
  s.setting || '/base/' || db.oid || '/' || c.relfilenode
FROM
  pg_settings s
  JOIN pg_database db on (s.name = 'data_directory')
  JOIN pg_class c on (datname = current_database())
  JOIN pg_namespace nsp on (c.relnamespace = nsp.oid)
WHERE
  relfilenode <> 0
  AND nsp.nspname !~ '^pg_'
  AND nsp.nspname <> 'information_schema';

Note that, as discussed earlier in this thread, this doesn't actually
answer what Edson was asking for.  Here's the query that would answer
his original request:

SELECT
  quote_ident(nsp.nspname) || '.' || quote_ident(c.relname),
  s.setting || '/base/' || db.oid || '/' || c.relfilenode,
  (pg_stat_file(s.setting || '/base/' || db.oid || '/' || c.relfilenode)).size as size
FROM 
  pg_settings s 
  JOIN pg_database db on (s.name = 'data_directory') 
  JOIN pg_class c on (datname = current_database()) 
  JOIN pg_namespace nsp on (c.relnamespace = nsp.oid) 
WHERE
  relfilenode <> 0 
  AND nsp.nspname !~ '^pg_'
  AND nsp.nspname <> 'information_schema';

Technically speaking, while these queries are correct for PG10, in prior
versions of PostgreSQL it's possible to have user schemas that begin
with 'pg_' and therefore the filtering in the WHERE clause would have to
be more specific.

Note that both of these need to be run as a superuser in older versions
of PG.  In PostgreSQL 10, a user could be GRANT'd 'pg_read_all_settings'
and be able to run the first query.  We don't currently support being
able to GRANT a non-superuser the ability to run pg_stat_file(), but
that will likely be coming in PG 11.

Thanks!

Stephen

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