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List: postgresql-general
Subject: Re: Introduction of a new field in pg_class indicating presence of a large object in a table
From: Tom Lane <tgl () sss ! pgh ! pa ! us>
Date: 2024-04-30 19:28:05
Message-ID: 1800617.1714505285 () sss ! pgh ! pa ! us
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"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Tue, Apr 30, 2024 at 11:57 AM Gaurav Pant <gauravpant145@gmail.com>
> wrote:
>> I wanted to know if there is any such system table that we can use to
>> identify and map the fields containing large objects and the respective
>> tables and if it is not already there, do we have any plans to incorporate
>> the same in pg_class like we have for pg_toast?
> Large Objects are nothing like TOAST. There is no system level association
> between large objects and tables. Sure, the DBA can choose to store a
> large object OID in a table, but how you'd go about figuring out which
> columns contain those is going to be installation specific.
Yeah. You might want to look at contrib/vacuumlo, but realize that
that's fairly heuristic.
> Though
> hopefully they used a bigint data type and maybe added "oid" to the column
> name...I suppose it would be interesting if one could define a FK on a
> table and point it at pg_largeobject_metadata but that I suspect would be
> the extent to which we'd do something along the lines of your request.
That would solve the opposite problem, of preventing a column from
containing any OIDs that *weren't* large object OIDs. Given that
recording a large object OID elsewhere in the database is purely
an application decision, I don't think there's a reasonable way
for the system to track it.
regards, tom lane
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