Horton

Re: tableam vs. TOAST

Peter Eisentraut <peter.eisentraut@2ndquadrant.com>

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From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
To: Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Prabhat Sahu <prabhat.sahu@enterprisedb.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-11-07T10:10:19Z
Lists: pgsql-hackers 
On 2019-11-06 18:00, Andres Freund wrote:
> I'd like an AM to have the *option* of implementing something better, or
> at least go in the direction of making that possible.

I don't think the presented design prevents that.  An AM can just return 
false from relation_needs_toast_table in all cases and implement 
something internally.

> It seems perfectly possible to have a helper function implementing the
> current logic that you just can call with the fixed chunk size as an
> additional parameter. Which'd basically mean there's no meaningful
> difference in complexity compared to providing the chunk size as an
> external AM property. In one case you have a callback that just calls a
> helper function with one parameter, in the other you fill in a member of
> the struct.

I can see a "moral" concern about having TOAST be part of the table AM 
API.  It should be an implementation concern of the AM.  How much more 
work would it be to refactor TOAST into a separate API that an AM 
implementation could use or not?  How much more complicated would the 
result be?  I guess you would like to at least have it explored.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

  1. tableam: New callback relation_fetch_toast_slice.

  2. tableam: Allow choice of toast AM.

  3. Move heap-specific detoasting logic into a separate function.

  4. Code cleanup for toast_fetch_datum and toast_fetch_datum_slice.

  5. Rename some toasting functions based on whether they are heap-specific.

  6. Create an API for inserting and deleting rows in TOAST tables.

  7. Split tuptoaster.c into three separate files.

  8. tableam: Move heap-specific logic from needs_toast_table below tableam.