[hibernate-dev] Memory consumption

[Steve Ebersole]

And I am certainly fine with allowing this to be a setting between the 3 
approaches:
1) Current approach using multiple loaders
2) Single loader approach using nulls to "fill out" slots
3) Single loader approach re-using keys to "fill out" slots

On 05/17/2012 10:42 AM, Steve Ebersole wrote:
> Besides, how is the plan any different for:
>
> ((id = null) OR (id = null) OR (id = null) OR (id = 4) OR (id = 5))
>
>
> On Thu 17 May 2012 10:40:57 AM CDT, Steve Ebersole wrote:
>> Its an index scan, totally trivial (unless their index hashing algos
>> are awful as well).
>>
>>
>> On Thu 17 May 2012 08:49:06 AM CDT, Guillaume Smet wrote:
>>> On Thu, May 17, 2012 at 3:02 PM, Steve Ebersole<steve at hibernate.org>
>>> wrote:
>>>> But just because you have 100 values in no way indicates how many
>>>> rows will
>>>> be returned. And I personally know of no optimizers that make such an
>>>> assumption; its a totally worthless assumption.
>>>
>>> That's why I put "simplified" in front of it.
>>>
>>> The number of clauses is taken into account to calculate the
>>> estimation of the number of rows returned and depending on the plan
>>> chosen to get the results, this might lead to results you don't expect
>>> and don't want.
>>>
>>> See the below example on PostgreSQL (which is far from having the
>>> worst optimizer/planner of the market):
>>> sitra=# explain select id from objettouristique where id=4 or id=4 or
>>> id=4 or id=4 or id=5;
>>> QUERY PLAN
>>> ------------------------------------------------------------------------------------------ 
>>>
>>>
>>> Bitmap Heap Scan on objettouristique (cost=1.80..2.41 rows=5 width=8)
>>> Recheck Cond: ((id = 4) OR (id = 4) OR (id = 4) OR (id = 4) OR (id = 
>>> 5))
>>> -> BitmapOr (cost=1.80..1.80 rows=5 width=0)
>>> -> Bitmap Index Scan on objettouristique_pkey
>>> (cost=0.00..0.36 rows=1 width=0)
>>> Index Cond: (id = 4)
>>> -> Bitmap Index Scan on objettouristique_pkey
>>> (cost=0.00..0.36 rows=1 width=0)
>>> Index Cond: (id = 4)
>>> -> Bitmap Index Scan on objettouristique_pkey
>>> (cost=0.00..0.36 rows=1 width=0)
>>> Index Cond: (id = 4)
>>> -> Bitmap Index Scan on objettouristique_pkey
>>> (cost=0.00..0.36 rows=1 width=0)
>>> Index Cond: (id = 4)
>>> -> Bitmap Index Scan on objettouristique_pkey
>>> (cost=0.00..0.36 rows=1 width=0)
>>> Index Cond: (id = 5)
>>>
>>> It sure looks stupid but the opinion of the PostgreSQL hackers is that
>>> it's stupid to add several times the same clause. The cost of checking
>>> all the conditions can be high and is wasted most of the time.
>>>
>>
>> -- 
>> steve at hibernate.org
>> http://hibernate.org
>
> -- 
> steve at hibernate.org
> http://hibernate.org