Horton

Re: [HACKERS] Custom compression methods

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Dilip Kumar <dilipbalaut@gmail.com>, Andres Freund <andres@anarazel.de>, Justin Pryzby <pryzby@telsasoft.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Alexander Korotkov <a.korotkov@postgrespro.ru>, David Steele <david@pgmasters.net>, Ildus Kurbangaliev <i.kurbangaliev@gmail.com>, Dmitry Dolgov <9erthalion6@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-03-19T23:54:39Z
Lists: pgsql-hackers 
On 2021-Mar-19, Robert Haas wrote:

> On Fri, Mar 19, 2021 at 6:22 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:

> > (At least, for binary upgrade surely you must make sure to apply the
> > correct setting regardless of defaults on either system).
> 
> It's not critical from a system integrity point of view; the catalog
> state just dictates what happens to new data.

Oh, okay.

> You could argue that if, in a future release, we change the default to
> lz4, it's good for pg_upgrade to migrate users to a set of column
> definitions that will use that for new data.

Agreed, that seems a worthy goal.

> > Maybe it makes sense to dump the compression clause if it is different
> > from pglz, regardless of the default on the source server.
> 
> Well, I really do hope that some day in the bright future, pglz will
> no longer be the thing we're shipping as the postgresql.conf default.
> So we'd just be postponing the noise until then. I think we need a
> better idea than that.

Hmm, why?  In that future, we can just change the pg_dump behavior to no
longer dump the compression clause if it's lz4 or whatever better
algorithm we choose.  So I think I'm clarifying my proposal to be "dump
the compression clause if it's different from the compiled-in default"
rather than "different from the GUC default".

-- 
Álvaro Herrera       Valdivia, Chile
"Para tener más hay que desear menos"

Commits

  1. docs: Update TOAST storage docs for configurable compression.

  2. Further tweaking of pg_dump's handling of default_toast_compression.

  3. Fix interaction of TOAST compression with expression indexes.

  4. Tidy up more loose ends related to configurable TOAST compression.

  5. Short-circuit slice requests that are for more than the object's size.

  6. Mostly-cosmetic adjustments of TOAST-related macros.

  7. Remove useless configure probe for <lz4/lz4.h>.

  8. Error on invalid TOAST compression in CREATE or ALTER TABLE.

  9. docs: Fix omissions related to configurable TOAST compression.

  10. More code cleanup for configurable TOAST compression.

  11. Bring configure support for LZ4 up to snuff.

  12. Make compression.sql regression test independent of default.

  13. Use valid compression method in brin_form_tuple

  14. Fix up pg_dump's handling of per-attribute compression options.

  15. Allow configurable LZ4 TOAST compression.

  16. Fix inconsistencies in the code

  17. Mostly-cosmetic improvements in memory chunk header alignment coding.

  18. Allow numeric to use a more compact, 2-byte header in many cases.