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Re: hiding variable-length fields from Form_pg_* structs

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Peter Eisentraut <peter_e(at)gmx(dot)net>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: hiding variable-length fields from Form_pg_* structs
Date: 2011-12-05 20:16:20
Message-ID: CA+TgmobN8rhxMNg=VMLm4W2hpbRGHk75pw31A3EjZ=api9-N=Q@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, Dec 5, 2011 at 3:12 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Mon, Dec 5, 2011 at 2:47 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
>>>> To clarify, I believe the rule is that the first variable-length field
>>>> can be accessed as a struct field.  Are there any exceptions to this?
>
>>> If it is known not null, yes, but I wonder just how many places actually
>>> depend on that.
>
>> My impression is that all the varlena fields also allow nulls.
>
> See MARKNOTNULL in bootstrap.c.  I think the exceptions were designed to
> protect direct accesses to pg_index.

Hmm, OK.

rhaas=# select r.relname, a.attname, a.atttypid::regtype from pg_class
r, pg_attribute a where relnamespace=11 and relkind='r' and attrelid =
r.oid and a.attnotnull and a.attlen<0;
  relname   |   attname    |  atttypid
------------+--------------+------------
 pg_proc    | proargtypes  | oidvector
 pg_index   | indkey       | int2vector
 pg_index   | indcollation | oidvector
 pg_index   | indclass     | oidvector
 pg_index   | indoption    | int2vector
 pg_trigger | tgattr       | int2vector
(6 rows)

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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