Re: [HACKERS] slow information schema with thausand users, seq.scan - Mailing list pgsql-patches

I have remove the LEFT part of the join to pg_roles in
psql/description.c.  I assume this is too risky for 8.1.X.

---------------------------------------------------------------------------

Tom Lane wrote:
> Andrew - Supernews <andrew+nonews@supernews.com> writes:
> > On 2006-02-06, Peter Eisentraut <peter_e@gmx.net> wrote:
> >> It already has indexes.
>
> > True, but they're not being used where you'd expect. This seems to be
> > something to do with the fact that it's not pg_authid which is being
> > accessed, but rather the view pg_roles.
>
> I looked into this and it seems the problem is that the view doesn't
> get flattened into the main query because of the has_nullable_targetlist
> limitation in prepjointree.c.  That's triggered because pg_roles has
>     '********'::text AS rolpassword
> which isn't nullable, meaning it would produce wrong behavior if
> referenced above the outer join.
>
> Ultimately, the reason this is a problem is that the planner deals only
> in simple Vars while processing joins; it doesn't want to think about
> expressions.  I'm starting to think that it may be time to fix this,
> because I've run into several related restrictions lately, but it seems
> like a nontrivial project.
>
> In the meantime, reducing the LEFT JOIN to pg_roles to a JOIN as per
> Peter's suggestion seems like the best short-term workaround.
>
>             regards, tom lane
>
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  Bruce Momjian                        |  http://candle.pha.pa.us
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Index: src/bin/psql/describe.c
===================================================================
RCS file: /cvsroot/pgsql/src/bin/psql/describe.c,v
retrieving revision 1.131
diff -c -c -r1.131 describe.c
*** src/bin/psql/describe.c    12 Feb 2006 03:22:19 -0000    1.131
--- src/bin/psql/describe.c    12 Feb 2006 19:26:31 -0000
***************
*** 194,200 ****
                            "\nFROM pg_catalog.pg_proc p"
          "\n     LEFT JOIN pg_catalog.pg_namespace n ON n.oid = p.pronamespace"
               "\n     LEFT JOIN pg_catalog.pg_language l ON l.oid = p.prolang"
!            "\n     LEFT JOIN pg_catalog.pg_roles r ON r.oid = p.proowner\n");

      /*
       * we skip in/out funcs by excluding functions that take or return cstring
--- 194,200 ----
                            "\nFROM pg_catalog.pg_proc p"
          "\n     LEFT JOIN pg_catalog.pg_namespace n ON n.oid = p.pronamespace"
               "\n     LEFT JOIN pg_catalog.pg_language l ON l.oid = p.prolang"
!            "\n     JOIN pg_catalog.pg_roles r ON r.oid = p.proowner\n");

      /*
       * we skip in/out funcs by excluding functions that take or return cstring
***************
*** 367,373 ****
                            _("Description"));
      appendPQExpBuffer(&buf,
                        "\nFROM pg_catalog.pg_database d"
!                   "\n  LEFT JOIN pg_catalog.pg_roles r ON d.datdba = r.oid\n"
                        "ORDER BY 1;");

      res = PSQLexec(buf.data, false);
--- 367,373 ----
                            _("Description"));
      appendPQExpBuffer(&buf,
                        "\nFROM pg_catalog.pg_database d"
!                   "\n  JOIN pg_catalog.pg_roles r ON d.datdba = r.oid\n"
                        "ORDER BY 1;");

      res = PSQLexec(buf.data, false);
***************
*** 1485,1491 ****

      appendPQExpBuffer(&buf,
                        "\nFROM pg_catalog.pg_class c"
!                "\n     LEFT JOIN pg_catalog.pg_roles r ON r.oid = c.relowner"
       "\n     LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace");
      if (showIndexes)
          appendPQExpBuffer(&buf,
--- 1485,1491 ----

      appendPQExpBuffer(&buf,
                        "\nFROM pg_catalog.pg_class c"
!                "\n     JOIN pg_catalog.pg_roles r ON r.oid = c.relowner"
       "\n     LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace");
      if (showIndexes)
          appendPQExpBuffer(&buf,
***************
*** 1727,1733 ****
                            _("Access privileges"), _("Description"));

      appendPQExpBuffer(&buf,
!          "\nFROM pg_catalog.pg_namespace n LEFT JOIN pg_catalog.pg_roles r\n"
                        "       ON n.nspowner=r.oid\n"
                        "WHERE    (n.nspname !~ '^pg_temp_' OR\n"
             "         n.nspname = (pg_catalog.current_schemas(true))[1])\n");        /* temp schema is first */
--- 1727,1733 ----
                            _("Access privileges"), _("Description"));

      appendPQExpBuffer(&buf,
!          "\nFROM pg_catalog.pg_namespace n JOIN pg_catalog.pg_roles r\n"
                        "       ON n.nspowner=r.oid\n"
                        "WHERE    (n.nspname !~ '^pg_temp_' OR\n"
             "         n.nspname = (pg_catalog.current_schemas(true))[1])\n");        /* temp schema is first */