Hi.
Ashutosh Bapat писал 2021-08-19 17:01:
I spent some time looking at this patch.
Generally it looks like a good idea. These stable functions will be
evaluated at the execution time and replaced with constants. I am not
sure whether the nodes saved in the param_list may not get the same
treatment. Have you verified that?
I'm not sure I understand you. All parameters are treated in the same
way.
They are evaluated in process_query_params(), real params and
parameters, corresponding to our SQLValue functions.
If we look at execution of something like
explain verbose select * from test1 t1 where i in (select i from test1
t2 where t2.t< now() and t1.i=t2.i) ;
QUERY PLAN
-------------------------------------------------------------------------------------------------------------------
Foreign Scan on public.test1 t1 (cost=100.00..243310.11 rows=930
width=20)
Output: t1.i, t1.t, t1.l
Filter: (SubPlan 1)
Remote SQL: SELECT i, t, l FROM data.test1
SubPlan 1
-> Foreign Scan on public.test1 t2 (cost=100.00..161.29 rows=5
width=4)
Output: t2.i
Remote SQL: SELECT i FROM data.test1 WHERE (($1::integer =
i)) AND ((t < $2::timestamp with time zone)
we can see two parameters evaluated in process_query_params(), one - of
T_Param type (with value of current t1.i) and one of T_SQLValueFunction
type (with value of current_timestamp).
Also the new node types being added to the param list is something
other than Param. So it conflicts with the comment below in
prepare_query_params()?
/*
* Prepare remote-parameter expressions for evaluation. (Note: in
* practice, we expect that all these expressions will be just
Params, so
* we could possibly do something more efficient than using the
full
* expression-eval machinery for this. But probably there would be
little
* benefit, and it'd require postgres_fdw to know more than is
desirable
* about Param evaluation.)
*/
If we are already adding non-params to this list, then the comment is
outdated?
Fixed comment in the new version of the patches.
--
Best regards,
Alexander Pyhalov,
Postgres Professional
