Re: Query not using index for user defined type
| От | Rodrigo Barboza |
|---|---|
| Тема | Re: Query not using index for user defined type |
| Дата | |
| Msg-id | CANs8QJZifmG13qTB9ohDDb=KfZRhBee5NK4vo=1ihBpneogVuA@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Query not using index for user defined type (Tom Lane <tgl@sss.pgh.pa.us>) |
| Ответы |
Re: Query not using index for user defined type
|
| Список | pgsql-hackers |
On Mon, Apr 15, 2013 at 5:33 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Using a seqscan to fetch 400 out of 1000 entries is the right thing.Rodrigo Barboza <rodrigombufrj@gmail.com> writes:
> I created a type 'mytype' (an unsigned int) and created an operator class
> for index.
> Then I created a table with a column of my type and isnerted 1000 entries.
> But no matter how many entries I have in the table, it never uses the
> index. It always does a seq scan.
> Here is the explain analyze with 1000 entries:
> explain analyze select * from mytable where a > 120::mytype and a <
> 530::mytype;
> ---------------------------------------------------------------------------------------------------
> Seq Scan on mytable (cost=0.00..19.02 rows=400 width=4) (actual
> time=0.023..0.229 rows=409 loops=1)
> Filter: ((a > '120'::mytype) AND (a < '530'::mytpe))
> Total runtime: 0.297 ms
(The crossover point where an index becomes unhelpful is a lot closer
to 1% of the table than it is to 40%.)
regards, tom lane
You were right Tom, when I did < 200 it used the index.
But I have another question.
I created a implic cast for mytype to bigint.
So when I do the same query it does seq scan, because the column is transformed into bigint.
Is there a good solution for this?
Here is an examples with the 2 queries.
explain analyze select * from mytable where a < 200::mytype;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------
Index Scan using mytype_idx on tm32 (cost=0.00..11.66 rows=195 width=4) (actual time=0.020..0.068 rows=200 loops=1)
Index Cond: (a < '200'::mytype)
Total runtime: 0.111 ms
explain analyze select * from mytable where a < 200;
QUERY PLAN
---------------------------------------------------------------------------------------------------
Seq Scan on mytable (cost=0.00..19.02 rows=334 width=4) (actual time=0.015..0.215 rows=200 loops=1)
Filter: ((a)::bigint < 200)
Total runtime: 0.238 ms
В списке pgsql-hackers по дате отправления: