Horton

Re: [HACKERS] Custom compression methods

Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>

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From: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Евгений Шишкин <itparanoia@gmail.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Oleg Bartunov <obartunov@gmail.com>, Craig Ringer <craig@2ndquadrant.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2017-11-20T15:44:35Z
Lists: pgsql-hackers 
On Mon, 20 Nov 2017 16:29:11 +0100
Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:

> On 11/20/2017 04:21 PM, Евгений Шишкин wrote:
> > 
> >   
> >> On Nov 20, 2017, at 18:18, Tomas Vondra
> >> <tomas.vondra@2ndquadrant.com
> >> <mailto:tomas.vondra@2ndquadrant.com>> wrote:
> >>
> >>
> >> I don't think we need to do anything smart here - it should behave
> >> just like dropping a data type, for example. That is, error out if
> >> there are columns using the compression method (without CASCADE),
> >> and drop all the columns (with CASCADE).  
> > 
> > What about instead of dropping column we leave data uncompressed?
> >   
> 
> That requires you to go through the data and rewrite the whole table.
> And I'm not aware of a DROP command doing that, instead they just drop
> the dependent objects (e.g. DROP TYPE, ...). So per PLOS the DROP
> COMPRESSION METHOD command should do that too.
> 
> But I'm wondering if ALTER COLUMN ... SET NOT COMPRESSED should do
> that (currently it only disables compression for new data).

If the table is big, decompression could take an eternity. That's why i
decided to only to disable it and the data could be decompressed using
compression options.

My idea was to keep compression options forever, since there will not
be much of them in one database. Still that requires that extension is
not removed.

I will try to find a way how to recompress data first in case it moves
to another table.

-- 
---
Ildus Kurbangaliev
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company

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.