Thank you Jeff
I tried on PostgreSQL 9.1.0, and found the running result is:
postgres=# explain execute s(*2*);
QUERY PLAN
--------------------------------------------------------------------------------
-
Bitmap Heap Scan on tst01 t (cost=*626.59*..*1486.25* rows=*33333* width=*
4*)
Recheck Cond: (id < $*1*)
-> Bitmap Index Scan on idx_tst01_id (cost=*0.00*..*618.26* rows=*33333
* width=*0*)
Index Cond: (id < $*1*)
(*4* rows)
postgres=# explain execute s(*10000*);
QUERY PLAN
--------------------------------------------------------------------------------
-
Bitmap Heap Scan on tst01 t (cost=*626.59*..*1486.25* rows=*33333* width=*
4*)
Recheck Cond: (id < $*1*)
-> Bitmap Index Scan on idx_tst01_id (cost=*0.00*..*618.26* rows=*33333
* width=*0*)
Index Cond: (id < $*1*)
(*4* rows)
postgres=#
I want to know some internal about the "parameterized path".
I guess that Before PG9.2,
After I called prepare command, the path and plan is already created
and done.
The plan is based on average estimation of all kinds of paths.
So even when I put different parameter, it just execute the same
finished plan.
2013/6/19 Jeff Janes <[email protected]>
> On Tue, Jun 18, 2013 at 2:09 AM, 高健 <[email protected]> wrote:
>
>
>
>> postgres=# explain execute s(2);
>>
>> QUERY PLAN
>>
>> ---------------------------------------------------------------------------------
>>
>> Index Only Scan using idx_tst01_id on tst01 t (cost=0.00..8.38 rows=1
>> width=4)
>>
>> Index Cond: (id < 2)
>>
>> (2 rows)
>>
>>
>> postgres=# explain execute s(100000);
>>
>> QUERY PLAN
>>
>> ---------------------------------------------------------------
>>
>> Seq Scan on tst01 t (cost=0.00..1693.00 rows=100000 width=4)
>>
>> Filter: (id < 100000)
>>
>> (2 rows)
>>
>>
>>
>> postgres=#
>>
>>
>>
>> When I just send sql of " select * from tst01 t where id <2" , it will
>> also produce index only scan plan.
>>
>> When I just send sql of " select * from tst01 t where id < 100000", it
>> will also produce seq scan plan.
>>
>>
>>
>> So I think that the above example can not show that "parameterized path"
>> has been created.
>>
>
> But if you try the PREPAREd sets in versions before 9.2, you will find
> they use the same plan as each other. Allowing them to differ based on the
> parameter they are executed with, just like the non-PREPARE ones differ, is
> what parameterized paths is all about.
>
> Cheers,
>
> Jeff
>
