Re: Move pg_attribute.attcompression to earlier in struct for reduced size?

On Tue, May 25, 2021 at 08:33:47PM -0500, Justin Pryzby wrote:
> It reminds me of reltablespace, which is stored as 0 to mean the database's
> default tablespace.
>
> Also, values are currently retoasted during vacuum full if their column's
> current compression method doesn't match the value's old compression.
>
> But it doesn't rewrite the column if the it used to use the default
> compression, and the default was changed. I think your idea would handle that.

Ah, the parallel with reltablespace and default_tablespace at database
level is a very good point. It is true that currently the code would
assign attcompression to a non-zero value once the relation is defined
depending on default_toast_compression set for the database, but
setting it to 0 in this case would be really helpful to change the
compression methods of all the relations if doing something as crazy
as a VACUUM FULL for this database. Count me as convinced.
--
Michael