Re: Make attstattarget nullable

Here is an updated patch rebased over 3e2e0d5ad7.

The 0001 patch stands on its own, but I also tacked on two additional
WIP patches that simplify some pg_attribute handling and make these
kinds of refactorings simpler in the future. See description in the
patches.

On 05.12.23 13:52, Peter Eisentraut wrote:
> In [0] it was discussed that we could make attstattarget a nullable
> column, instead of always storing an explicit -1 default value for most
> columns.  This patch implements this.
>
> This changes the pg_attribute field attstattarget into a nullable field
> in the variable-length part of the row.  If no value is set by the user
> for attstattarget, it is now null instead of previously -1.  This saves
> space in pg_attribute and tuple descriptors for most practical
> scenarios.  (ATTRIBUTE_FIXED_PART_SIZE is reduced from 108 to 104.)
> Also, null is the semantically more correct value.
>
> The ANALYZE code internally continues to represent the default
> statistics target by -1, so that that code can avoid having to deal with
> null values.  But that is now contained to ANALYZE code.  The DDL code
> deals with attstattarget possibly null.
>
> For system columns, the field is now always null but the effective value
> 0 (don't analyze) is assumed.
>
> To set a column's statistics target to the default value, the new
> command form ALTER TABLE ... SET STATISTICS DEFAULT can be used.  (SET
> STATISTICS -1 still works.)
>
>
> [0]:
> https://www.postgresql.org/message-id/flat/d07ffc2b-e0e8-77f7-38fb-be921dff71af%40enterprisedb.com