Re: explain plans with information about (modified) gucs

Tomas Vondra-4 wrote
> Hello Sergei,
> 
>> This patch correlates with my proposal
>> "add session information column to pg_stat_statements"
>> https://www.postgresql.org/message-id/3aa097d7-7c47-187b-5913-db8366cd4491%40gmail.com
>> They both address the problem to identify the factors that make
>> different execution plans for the same SQL statements. You are
>> interested in the current settings that affect the execution plan, I'm
>> concerned about historical data in pg_stat_statements. From my
>> experience the most often offending settings are
>> current_schemas/search_path and current_user. Please have in mind that
>> probably the same approach that you will use to extend explain plan
>> functionality will be eventually implemented to extend
>> pg_stat_statements.
> 
> Possibly, although I don't have an ambition to export the GUCs into
> pg_stat_statements in this patch. There's an issue with merging
> different values of GUCs in different executions of a statement, and
> it's unclear how to solve that.
> 
> [...]
> 
> -- 
> Tomas Vondra                  http://www.2ndQuadrant.com
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

This explain with GUCs feature can be included very easily for historical
data management in pg_store_plans or pg_stat_sql_plans extensions 
(that both use a planid based on the normalized plan text).

Regards
PAscal



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