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

On Fri, 7 Jul 2023 17:21:36 +0900
Yugo NAGATA <nagata@sraoss.co.jp> wrote:

> Hi Nikita,
> 
> On Wed, 5 Jul 2023 17:49:20 +0300
> Nikita Malakhov <hukutoc@gmail.com> wrote:
> 
> > Hi!
> > 
> > I like the idea of having a standard function which shows a TOAST value ID
> > for a row. I've used my own to handle TOAST errors. Just, maybe, more
> > correct
> > name would be "...value_id", because you actually retrieve valueid field
> > from the TOAST pointer, and chunk ID consists of valueid + chunk_seq.
> 
> Thank you for your review!
> 
> Although, the retrieved field is "va_valueid" and it is called "value ID" in the
> code, I chose the name "..._chunk_id" because I found the description in the
> documentation as followings:
> 
> -------------
> Every TOAST table has the columns chunk_id (an OID identifying the particular TOASTed value), chunk_seq (a sequence
numberfor the chunk within its value), and chunk_data (the actual data of the chunk). A unique index on chunk_id and
chunk_seqprovides fast retrieval of the values. A pointer datum representing an out-of-line on-disk TOASTed value
thereforeneeds to store the OID of the TOAST table in which to look and the OID of the specific value (its chunk_id)
 
> -------------
> https://www.postgresql.org/docs/devel/storage-toast.html
> 
> Here, chunk_id defined separately from chunk_seq. Therefore, I wonder  
> pg_column_toast_chunk_id would be ok. However, I don't insist on this
> and I would be happy to change it if the other name is more natural for users.

I attached v2 patch that contains the documentation fix.

Regards,
Yugo Nagata

> 
> Regards,
> Yugo Nagata
> 
> > 
> > -- 
> > Regards,
> > Nikita Malakhov
> > Postgres Professional
> > The Russian Postgres Company
> > https://postgrespro.ru/
> 
> 
> -- 
> Yugo NAGATA <nagata@sraoss.co.jp>
> 
> 


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