Re: BUG #14607: session variables are non-deterministic

Hi

2017-03-31 14:35 GMT+02:00 <jankaraffa(at)gmail(dot)com>:

> The following bug has been logged on the website:
>
> Bug reference: 14607
> Logged by: Jan Karaffa
> Email address: jankaraffa(at)gmail(dot)com
> PostgreSQL version: 9.4.11
> Operating system: Red Hat 4.4.7-17, 64bit
> Description:
>
> let's have myPartTable as partitioned table with check constraint on
> part_key::text column
>
> SET myvar.partition_key='ABC';
> select count(*) from myPartTable
> where part_key = current_setting('myvar.partition_key')::text;
>
> Execution plan shows that all inherited (partitioned) tables are scanned.
> It
> behaves like current_setting function is non-deterministic and therefore
> sql
> optimalizator is not considered output as constant. For me it looks like
> bug
> as session variable can not change during parsing/execution.
>
> If current_setting function would behave deterministic it would enable us
> to
> pass session parameters into the view and perform limitation inside of view
> where it makes sense. Current "workaround" is to move logic from view to
> function, which is not as easy to use in hibernate as the standard views.
>

session variable is volatile - so it is not bug.

There is a workaround - you can wrap a access to this variable to STABLE
function

CREATE OR REPLACE FUNCTION varval(text)
RETURNS text AS $$
SELECT current_setting($1)
$$ LANGUAGE SQL STABLE;

select count(*) from myPartTable
where part_key = varval('myvar.partition_key')::text;

should to work for you

Regards

Pavel

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