Re: Bitmap Heap scan 8.1/8.2

Pavel Stehule wrote:
> 2007/10/22, Martin Marques <martin@bugs.unl.edu.ar>:
>> Pavel Stehule wrote:
>>> 2007/10/22, Martin Marques <martin@bugs.unl.edu.ar>:
>>>> Pavel Stehule wrote:
>>>>> Hello
>>>>>
>>>>> I am unsure, did you check config values?
>>>> Don't know which ones you are talking about, but all enable_* are set to on.
>>>>
>>>> Anything else?
>>>>
>>> shared_buffers
>> 8.1:
>>
>>   16000
> ~ 128M
>>
>> 8.2:
>>
>>   400MB
>>
>>
>>> work_mem
>> 8.1:
>>
>>   8192
> 8M !!!! 8>4
>> 8.2:
>>
>>   4MB
>>
>>
>>> effective_cache_size
>> 8.1:
>>
>>   1000
> 8M
>> 8.2:
>>
>>   128MB
>>
>>
>
> try
>
> set work_mem to '8MB';
> and
> explain analyze select ..

These things didn't help. What changed the plan completely was this:

seq_page_cost = 5.0                     # measured on an arbitrary scale
cpu_tuple_cost = 0.05                   # same scale as above

Specially the first one. Now I get this:

explain analyze SELECT usuarios,nticket,objeto,vencimiento FROM
prestamos WHERE biblioteca = 19 AND  vencimiento < now() AND NOT
devuelto ORDER BY vencimiento DESC;

QUERY PLAN

--------------------------------------------------------------------------------------------------------------------------------------------------------
  Sort  (cost=7058.86..7060.86 rows=800 width=20) (actual
time=22.850..22.888 rows=95 loops=1)
    Sort Key: vencimiento
    ->  Index Scan using prestamos_objetos_devuelto_idx on prestamos
(cost=0.00..7020.28 rows=800 width=20) (actual time=0.346..22.590
rows=95 loops=1)
          Index Cond: (devuelto = false)
          Filter: ((biblioteca = 19) AND (vencimiento < now()) AND (NOT
devuelto))
  Total runtime: 22.973 ms


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