Re: pg_column_toast_chunk_id: a function to get a chunk ID of a TOASTed value

On Tue, 30 Jan 2024 12:12:31 +0800
jian he <jian.universality@gmail.com> wrote:

> On Fri, Jan 26, 2024 at 8:42 AM Yugo NAGATA <nagata@sraoss.co.jp> wrote:
> >
> > On Tue, 2 Jan 2024 08:00:00 +0800
> > jian he <jian.universality@gmail.com> wrote:
> >
> > > On Mon, Nov 6, 2023 at 8:00 AM jian he <jian.universality@gmail.com> wrote:
> > > >
> > > > minor doc issues.
> > > > Returns the chunk id of the TOASTed value, or NULL if the value is not TOASTed.
> > > > Should it be "chunk_id"?
> >
> > Thank you for your suggestion. As you pointed out, it is called "chunk_id"
> > in the documentation, so I rewrote it and also added a link to the section
> > where the TOAST table structure is explained.
> >
> > > > you may place it after pg_create_logical_replication_slot entry to
> > > > make it look like alphabetical order.
> >
> > I've been thinking about where we should place the function in the doc,
> > and I decided place it in the table  of Database Object Size Functions
> > because I think pg_column_toast_chunk_id also would assist understanding
> > the result of size functions as similar to pg_column_compression; that is,
> > those function can explain why a large value in size could be stored in
> > a column.
> 
> diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
> index 210c7c0b02..2d82331323 100644
> --- a/doc/src/sgml/func.sgml
> +++ b/doc/src/sgml/func.sgml
> @@ -28078,6 +28078,23 @@ postgres=# SELECT '0/0'::pg_lsn +
> pd.segment_number * ps.setting::int + :offset
>         </para></entry>
>        </row>
> 
> +      <row>
> +       <entry role="func_table_entry"><para role="func_signature">
> +        <indexterm>
> +         <primary>pg_column_toast_chunk_id</primary>
> +        </indexterm>
> +        <function>pg_column_toast_chunk_id</function> ( <type>"any"</type> )
> +        <returnvalue>oid</returnvalue>
> +       </para>
> +       <para>
> +        Shows the <structfield>chunk_id</structfield> of an on-disk
> +        <acronym>TOAST</acronym>ed value. Returns <literal>NULL</literal>
> +        if the value is un-<acronym>TOAST</acronym>ed or not on-disk.
> +        See <xref linkend="storage-toast-ondisk"/> for details about
> +        <acronym>TOAST</acronym>.
> +       </para></entry>
> +      </row>
> 
> v3 patch will place it on `Table 9.97. Replication Management Functions`
> I agree with you. it should be placed after pg_column_compression. but
> apply your patch, it will be at
> 
> 
> > > > There is no test. maybe we can add following to src/test/regress/sql/misc.sql
> > > > create table val(t text);
> > > > INSERT into val(t) SELECT string_agg(
> > > >   chr((ascii('B') + round(random() * 25)) :: integer),'')
> > > > FROM generate_series(1,2500);
> > > > select pg_column_toast_chunk_id(t) is  not null from val;
> > > > drop table val;
> >
> > Thank you for the test proposal. However, if we add a test, I want
> > to check that the chunk_id returned by the function exists in the
> > TOAST table, and that it returns NULL if the values is not TOASTed.
> > For the purpose, I wrote a test using a dynamic SQL since the table
> > name of the TOAST table have to be generated from the main table's OID.
> >
> > > Hi
> > > the main C function (pg_column_toast_chunk_id)  I didn't change.
> > > I added tests as mentioned above.
> > > tests put it on src/test/regress/sql/misc.sql, i hope that's fine.
> > > I placed pg_column_toast_chunk_id in "Table 9.99. Database Object
> > > Location Functions" (below Table 9.98. Database Object Size
> > > Functions).
> >
> > I could not find any change in your patch from my previous patch.
> > Maybe, you attached wrong file. I attached a patch updated based
> > on your review, including the documentation fixes and a test.
> > What do you think about this it?
> >
> 
> sorry, I had attached the wrong file.
> but your v3 also has no tests, documentation didn't fix.
> maybe you also attached the wrong file too?
> 

Sorry, I also attached a wrong file.
Attached is the correct one.

Regards,
Yugo Nagata


-- 
Yugo NAGATA <nagata@sraoss.co.jp>