Horton

Re: extended stats on partitioned tables

Tomas Vondra <tomas.vondra@enterprisedb.com>

View thread View on postgr.es
From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: Zhihong Yu <zyu@yugabyte.com>, Jaime Casanova <jcasanov@systemguards.com.ec>, pgsql-hackers@postgresql.org
Date: 2021-12-12T21:29:39Z
Lists: pgsql-hackers

Attachments

On 12/12/21 18:52, Justin Pryzby wrote:
> +          * XXX Can't we simply look at rte->inh?
> +          */
> +         inh = root->append_rel_array == NULL ? false :
> +                 root->append_rel_array[onerel->relid]->parent_relid != 0;
> 
> I think so.  That's what I came up with while trying to figured this out, and
> it's no great surprise that it needed to be cleaned up - thanks.
> 

OK, fixed.

> In your 0003 patch, the "if inh: break" isn't removed from examine_variable(),
> but the corresponding thing is removed everywhere else.
> 

Ah, you're right. And it wasn't updated in the 0002 patch either - it
should do the relkind check too, to allow partitioned tables. Fixed.

> In 0003, mcv_clauselist_selectivity still uses simple_rte_array rather than
> rt_fetch.
> 

That's mostly a conscious choice, so that I don't have to include
parsetree.h. But maybe that'd be better ...

> The regression tests changed as a result of not populating stx_data; I think
> it's may be better to update like this:
> 
> SELECT stxname, stxdndistinct, stxddependencies, stxdmcv, stxoid IS NULL
>   FROM pg_statistic_ext s LEFT JOIN pg_statistic_ext_data d
>   ON d.stxoid = s.oid
>   WHERE s.stxname = 'ab1_a_b_stats';
> 

Not sure I understand. Why would this be better than inner join?

> There's this part about documentation for the changes in backbranches:
> 
> On Sun, Sep 26, 2021 at 03:25:50PM -0500, Justin Pryzby wrote:
>> Also, I think in backbranches we should document what's being stored in
>> pg_statistic_ext, since it's pretty unintuitive:
>>  - noninherted stats (FROM ONLY) for inheritence parents;
>>  - inherted stats (FROM *) for partitioned tables;
> 
> spellcheck: inheritence should be inheritance.
> 

Thanks, fixed. Can you read through the commit messages and check the
attribution is correct for all the patches?

> All for now.  I'm going to update the regression tests for dependencies and the
> other code paths.
> 

Thanks!

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. Add stxdinherit flag to pg_statistic_ext_data

  2. Build inherited extended stats on partitioned tables

  3. Ignore extended statistics for inheritance trees

  4. Don't build extended statistics on inheritance trees

  5. Tighten up relation kind checks for extended statistics

  6. Avoid assuming that statistics for a parent relation reflect the properties of