Message-ID: <5e048736-26bd-4254-84fa-c74ad0bf0c88@dunslane.net>
Date: Thu, 12 Mar 2026 10:09:03 -0400
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: BUG #19431: limitation of the data type jsonb equals 8Kb
To: perovaa@sbermarketing.ru, pgsql-bugs@lists.postgresql.org
References: <19431-0a33306c00df939f@postgresql.org>
From: Andrew Dunstan <andrew@dunslane.net>
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On 2026-03-12 Th 8:11 AM, PG Bug reporting form wrote:
> The following bug has been logged on the website:
>
> Bug reference:      19431
> Logged by:          Alex Perov
> Email address:      perovaa@sbermarketing.ru
> PostgreSQL version: 18.3
> Operating system:   Windows 10
> Description:
>
> Hello.
> I have a type:
> CREATE TYPE public.t_dict AS
> (
>          id bigint,
>          name text,
>          gid uuid,
>          alias text,
>          bgcolor text,
>          disabled boolean,
>          checked boolean,
>          options jsonb,
>          "order" integer
> );
> and function
> CREATE OR REPLACE FUNCTION public.f_func(data jsonb, uid bigint, context
> text = null, ext text = null, pid bigint = null, pgid uuid = null)
>          returns setof rd.t_dict
>          language plpgsql
> AS $$
> begin
>    context := coalesce(context, data->>'context', '');
>    ext = coalesce(ext, '');
>
>    create temp table tmp_f_table of public.t_dict;
>    if dict = 'dict1' then
>      insert into tmp_f_table (id, name)
>        select
>            1, name
>          from public.tbl1 a;
>    elsif dict = 'dict2' then
>      insert into tmp_f_table (id, name, alias)
>        select
>            t.objecttypeid, t.objecttype, t.alias
>          from public.tbl2 t
>          where (t.objecttypeid <> 0)
>            and t.active;
>    elsif dict = 'dict3' then
>      insert into tmp_f_table (id, name, options)
>      select
>            t.linktypeid, t.linktype,
>            json_object(
>              'rev': t.reftypeid = (data->'objecttype')::bigint,
>              'items': t.options
>            )
>          from public.tbl3 t;
>    end if;
> return query select * from tmp_f_cpdictionary;
>    drop table tmp_f_cpdictionary;
> end
> $$;
> when calling a function for dict3, I have an error "could not open relation
> with OID 196327".
> As far as I know, this is due to a limitation of the data type jsonb equals
> 8Kb.
> Is it possible to fix this error without changing the logic of the code?
>

This has nothing to do with any limit on the size of jsonb, and in fact 
jsonb can have values vastly larger than 8Kb.

The real problem is the well-known plan caching + temp table OID 
mismatch issue. Here's what's actually happening:

   1. The function does CREATE TEMP TABLE tmp_f_table OF public.t_dict 
at the start and DROP TABLE tmp_f_table at the end.
   2. On the first call, PL/pgSQL parses/plans the INSERT INTO 
tmp_f_table and SELECT * FROM tmp_f_table statements, caching plans that 
reference tmp_f_table by its OID (e.g., OID 196327).
   3. On a subsequent call, the old temp table has been dropped and a 
new one is created with a different OID. The cached plan still 
references the old OID leading to "could not open relation with OID 196327".

This is a classic pitfall documented in the PostgreSQL manual under 
PL/pgSQL plan caching.

cheers


andrew

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