Re: [HACKERS] How to get the 'ctid' from a record type?
| От | Eric Ridge |
|---|---|
| Тема | Re: [HACKERS] How to get the 'ctid' from a record type? |
| Дата | |
| Msg-id | CANcm6waPLx3KRR0rioBfMRn8kJwD_-+C4nZLDMueKr+u9dn-7Q@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: [HACKERS] How to get the 'ctid' from a record type? (Tom Lane <tgl@sss.pgh.pa.us>) |
| Ответы |
Re: [HACKERS] How to get the 'ctid' from a record type?
Re: [HACKERS] How to get the 'ctid' from a record type? |
| Список | pgsql-hackers |
I suspect the tuple at (0,1) has been the subject of a failed update.
Yep.
Your problem here is that you're mistaking the t_ctid field of a tuple
header for the tuple's address. It is not that; it's really just garbage
normally, and is only useful to link forward to the next version of the
row from an outdated tuple. I think we do initialize it to the tuple's
own address during an INSERT, but either a completed or failed UPDATE
would change it.
Thanks. That helps clarify the comments in htup_details.h, actually.
I do not think there is any way to get the true address of a heap tuple
out of a composite Datum manufactured from the tuple. Most of the other
system columns can't be gotten from a composite Datum either, because of
the field overlay in HeapTupleHeaderData's union t_choice.
Well shoot. That kinda spoils my plans.
What about this? Is the tuple currently being evaluated (I suppose in the case of a sequential scan) available in the context of a function call?
Thanks again for your time! It's much appreciated.
eric
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