> O
>>>>> Sorry, maybe my question wasn't clear enough.
>>>>>
>>>>> A query can be rewritten in various ways by applying rules and costs of
>>>>> relational algebra operators, as well as their parallelisation. I am
>>>>> talking about turning off this query optimization, so I am already
>>>>> assuming that indexes aren't present.
>>>>
>>>> Have you played with any of these settings?
>>>>
>>>> postgres=# select version();
>>>> version
>>>> ---------------------------------------------------------------------------------------------------------
>>>> PostgreSQL 10.7 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-36), 64-bit
>>>> (1 row)
>>>>
>>>> postgres=# select name, setting, unit,short_desc from pg_settings where name ~ 'para';
>>>> name | setting | unit | short_desc
>>>> ---------------------------------+---------+------+----------------------------------------------------------------------------------------------------
>>>> force_parallel_mode | off | | Forces use of parallel query facilities.
>>>> max_parallel_workers | 16 | | Sets the maximum number of parallel workers that can be active at one time.
>>>> max_parallel_workers_per_gather | 8 | | Sets the maximum number of parallel processes per executor node.
>>>> min_parallel_index_scan_size | 64 | 8kB | Sets the minimum amount of index data for a parallel scan.
>>>> min_parallel_table_scan_size | 1024 | 8kB | Sets the minimum amount of table data for a parallel scan.
>>>> parallel_setup_cost | 1000 | | Sets the planner's estimate of the cost of starting up worker processes for parallel query.
>>>> parallel_tuple_cost | 0.1 | | Sets the planner's estimate of the cost of passing each tuple (row) from worker to master backend.
>>>> ssl_dh_params_file | | | Location of the SSL DH parameters file.
>>>> (8 rows)
>>>>
>>> Well not the last one of course.
>>
>> Better yet, “where category ~* ‘planner’"
>>
>
> Hi
>
> Yes, I've taken a look. I'm just interested in turning off the whole
> module and there is no parameter to do just that - an on and off switch
> - from what I can understand. What I can do instead is to go over the
> entire list of parameters and configure them each to generate a bad
> plan, but I'm not sure in general how to make a configuration which
> gives me the worst plan possible under all situations.
>
> I was hoping that someone has the on/off switch I'm looking for or a
> parameter template which has been used for the same purpose or something
> along these lines...
>
> This document describes the module I'm talking about:
> https://www.postgresql.org/docs/current/planner-optimizer.html <https://www.postgresql.org/docs/current/planner-optimizer.html>
Yeah, I guess I read that to say postgres will optimize generically (after geqo_threshold). Now maybe that’s the worst plan? Per force a lot of seq-scans in the absence of any indices. And if it isn’t the worst possible plan, so what, you’re using postgres, you won’t get a worse plan without lying to the optimizer.
But I’m clearly in over my head. The pros will be along shortly, I’m sure.