Horton

Re: [HACKERS] Custom compression methods

Tomas Vondra <tomas.vondra@2ndquadrant.com>

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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>
Cc: pgsql-hackers@postgresql.org, Ildar Musin <i.musin@postgrespro.ru>
Date: 2017-11-25T01:13:41Z
Lists: pgsql-hackers 
Hi,

On 11/24/2017 10:38 AM, Ildus Kurbangaliev wrote:
> ...
> That means compressed datums now in the column with storage
> specified as external. I'm not sure that's a bug or a feature.
>

Interesting. Never realized it behaves like this. Not sure if it's
intentional or not (i.e. bug vs. feature).

> Lets insert them usual way:
> 
>   delete from t2;
>   insert into t2 select repeat(md5(i::text),300) from
>     generate_series(1,100000) s(i);
>   \d+
> 
>                      List of relations
>    Schema | Name | Type  | Owner |  Size   | Description 
>   --------+------+-------+-------+---------+-------------
>    public | t1   | table | ildus | 18 MB   | 
>    public | t2   | table | ildus | 1011 MB | 
> 
> Maybe there should be more common solution like comparison of
> attribute properties?
> 

Maybe, not sure what the right solution is. I just know that if we allow
inserting data into arbitrary tables without recompression, we may end
up with data that can't be decompressed.

I agree that the behavior with extended storage is somewhat similar, but
the important distinction is that while that is surprising the data is
still accessible.

regards

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

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.