statistics about tamp tables ...

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От Hans-Jürgen Schönig
Тема statistics about tamp tables ...
Дата
Msg-id 3FC46D2C.8070501@cybertec.at
обсуждение исходный текст
Ответы Re: statistics about tamp tables ...
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Recently I have come across a simple issue which made me think about it.
When we create a tmp table (SELECT INTO, CREATE TABLE AS) the planner 
won't know anything about its content after creating it.
Many people use temp tables heavy when the amount of data for a certain 
analysis has to be reduced significantly. Frequently the same tmp table 
is queried quite frequently. In order to speed those scenarios up it can 
be useful to vacuum those tmp tables so that the planner will find more 
clever joins.
Is it possible and does it make sense to generate those statistics on 
the fly (during CREATE TABLE AS)? Maybe we could have a GUC which tells 
the system whether to generate statistics or not.

test=# select * from test; id
----  4  4
(2 rows)

test=# VACUUM test ;
VACUUM

test=# explain select * from test ;                     QUERY PLAN
---------------------------------------------------- Seq Scan on test  (cost=0.00..1.02 rows=2 width=4)
(1 row)



test=# select * into tmp from test;
SELECT
test=# explain select * from tmp;                      QUERY PLAN
------------------------------------------------------- Seq Scan on tmp  (cost=0.00..20.00 rows=1000 width=4)
(1 row)

Best regards,        Hans

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