Re: Materializing the relation

>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)

On 6/11/07, rupesh bajaj <rupesh(dot)bajaj(at)gmail(dot)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
>