| From: | Ashwin Agrawal <aagrawal(at)pivotal(dot)io> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Rafia Sabih <rafia(dot)pghackers(at)gmail(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Asim R P <apraveen(at)pivotal(dot)io>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> |
| Subject: | Re: Pluggable Storage - Andres's take |
| Date: | 2019-05-08 06:18:39 |
| Message-ID: | CALfoeit60N+7r0qRH5y=WzVAzz7qx-CkoS-+OnSi4orHUv692g@mail.gmail.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
On Mon, May 6, 2019 at 1:39 PM Ashwin Agrawal <aagrawal(at)pivotal(dot)io> wrote:
>
> Also wish to point out, while working on Zedstore, we realized that
> TupleDesc from Relation object can be trusted at AM layer for
> scan_begin() API. As for ALTER TABLE rewrite case (ATRewriteTables()),
> catalog is updated first and hence the relation object passed to AM
> layer reflects new TupleDesc. For heapam its fine as it doesn't use
> the TupleDesc today during scans in AM layer for scan_getnextslot().
> Only TupleDesc which can trusted and matches the on-disk layout of the
> tuple for scans hence is from TupleTableSlot. Which is little
> unfortunate as TupleTableSlot is only available in scan_getnextslot(),
> and not in scan_begin(). Means if AM wishes to do some initialization
> based on TupleDesc for scans can't be done in scan_begin() and forced
> to delay till has access to TupleTableSlot. We should at least add
> comment for scan_begin() to strongly clarify not to trust Relation
> object TupleDesc. Or maybe other alternative would be have separate
> API for rewrite case.
Just to correct my typo, I wish to say, TupleDesc from Relation object can't
be trusted at AM layer for scan_begin() API.
Andres, any thoughts on above. I see you had proposed "change the
table_beginscan* API so it
provides a slot" in [1], but seems received no response/comments that time.
[1]
https://www.postgresql.org/message-id/20181211021340.mqaown4njtcgrjvr%40alap3.anarazel.de
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Thomas Munro | 2019-05-08 06:31:04 | Adding SMGR discriminator to buffer tags |
| Previous Message | Thomas Munro | 2019-05-08 06:04:06 | Re: Copy data to DSA area |