Re: An improvement on parallel DISTINCT
| От | Richard Guo |
|---|---|
| Тема | Re: An improvement on parallel DISTINCT |
| Дата | |
| Msg-id | CAMbWs4_=f9gr+DyYoP9WtGbtfJTHM_CZmqrUkYhQ+TuOjhs9qQ@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: An improvement on parallel DISTINCT (David Rowley <dgrowleyml@gmail.com>) |
| Ответы |
Re: An improvement on parallel DISTINCT
|
| Список | pgsql-hackers |
On Fri, Feb 2, 2024 at 7:36 PM David Rowley <dgrowleyml@gmail.com> wrote:
Now for the other stuff you had. I didn't really like this part:
+ /*
+ * Set target for partial_distinct_rel as generate_useful_gather_paths
+ * requires that the input rel has a valid reltarget.
+ */
+ partial_distinct_rel->reltarget = cheapest_partial_path->pathtarget;
I think we should just make it work the same way as
create_grouping_paths(), where grouping_target is passed as a
parameter.
I've done it that way in the attached.
The change looks good to me.
BTW, I kind of doubt that 'create_partial_distinct_paths' is a proper
function name given what it actually does. It not only generates
distinct paths based on input_rel's partial paths, but also adds
Gather/GatherMerge on top of these partially distinct paths, followed by
a final unique/aggregate path to ensure uniqueness of the final result.
So maybe 'create_parallel_distinct_paths' or something like that would
be better?
I asked because I noticed that in create_partial_grouping_paths(), we
only generate partially aggregated paths, and any subsequent
FinalizeAggregate step is called in the caller.
Thanks
Richard
BTW, I kind of doubt that 'create_partial_distinct_paths' is a proper
function name given what it actually does. It not only generates
distinct paths based on input_rel's partial paths, but also adds
Gather/GatherMerge on top of these partially distinct paths, followed by
a final unique/aggregate path to ensure uniqueness of the final result.
So maybe 'create_parallel_distinct_paths' or something like that would
be better?
I asked because I noticed that in create_partial_grouping_paths(), we
only generate partially aggregated paths, and any subsequent
FinalizeAggregate step is called in the caller.
Thanks
Richard
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