Re: Materializing the relation
| От | Shoaib Mir |
|---|---|
| Тема | Re: Materializing the relation |
| Дата | |
| Msg-id | bf54be870706110844p9180055n64ff1a3dd7776c28@mail.gmail.com обсуждение исходный текст |
| Ответ на | Materializing the relation ("rupesh bajaj" <rupesh.bajaj@gmail.com>) |
| Ответы |
Re: Materializing the relation
|
| Список | pgsql-general |
From /src/include/utils/tuplestore.h
"The materialize shields the sort from the need to do mark/restore and thereby allows it to perform its final merge pass on-the-fly; while the materialize itself is normally cheap since it won't spill to disk unless the number of tuples with equal key values exceeds work_mem"
--
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)
"The materialize shields the sort from the need to do mark/restore and thereby allows it to perform its final merge pass on-the-fly; while the materialize itself is normally cheap since it won't spill to disk unless the number of tuples with equal key values exceeds work_mem"
--
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)
On 6/11/07, rupesh bajaj < rupesh.bajaj@gmail.com> wrote:
Hi,
What is the meaning of 'materializing' a relation after sequential scan?
explain select * from tb1, tb2 where tb1.c1 = tb2.c2;
QUERY PLAN
----------------------------------------------------------------
Nested Loop (cost=1.03..2.34 rows=3 width=24)
Join Filter: (tb1.c1 = tb2.c1)
-> Seq Scan on tb2 (cost=0.00..1.04 rows=4 width=12)
-> Materialize (cost=1.03..1.06 rows=3 width=12)
-> Seq Scan on tb1 (cost= 0.00..1.03 rows=3 width=12)
In this above plan, what does 'Material' mean?
Thanks,
Rupesh
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