Re: [PATCH] Incremental sort (was: PoC: Partial sort)
От | Tomas Vondra |
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Тема | Re: [PATCH] Incremental sort (was: PoC: Partial sort) |
Дата | |
Msg-id | 20190928230049.k4l2mayun7jomhxy@development обсуждение исходный текст |
Ответ на | Re: [PATCH] Incremental sort (was: PoC: Partial sort) (James Coleman <jtc331@gmail.com>) |
Ответы |
Re: [PATCH] Incremental sort (was: PoC: Partial sort)
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Список | pgsql-hackers |
On Fri, Sep 27, 2019 at 01:50:30PM -0400, James Coleman wrote: >On Mon, Sep 9, 2019 at 5:55 PM Tomas Vondra ><tomas.vondra@2ndquadrant.com> wrote: >> The "patched" column means all developer GUCs disabled, so it's expected >> to produce the same plan as master (and it is). And then there's one >> column for each developer GUC. If the column is just TRUE it means the >> GUC does not affect any of the synthetic queries. There are 4 of them: >> >> - devel_add_paths_to_grouping_rel_parallel >> - devel_create_partial_grouping_paths >> - devel_gather_grouping_paths >> - devel_standard_join_search >> >> The places controlled by those GUCs are either useless, or the query >> affected by them is not included in the list of queries. > >I'd previously found (in my reverse engineering efforts) the query: > >select * >from tenk1 t1 >join tenk1 t2 on t1.hundred = t2.hundred >join tenk1 t3 on t1.hundred = t3.hundred >order by t1.hundred, t1.twenty >limit 50; > >can change plans to use incremental sort when >generate_useful_gather_paths() is added to standard_join_search(). >Specifically, we get a merge join between t1 and t3 as the top level >(besides limit) node where the driving side of the join is a gather >merge with incremental sort. This does rely on these gucs set in the >test harness: > >set local max_parallel_workers_per_gather=4; >set local min_parallel_table_scan_size=0; >set local parallel_tuple_cost=0; >set local parallel_setup_cost=0; > >So I think we can reduce the number of unused gucs to 3. > OK. I'll try extending the set of synthetic queries in [1] to also do soemthing like this and generate similar plans. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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