Re: Why performance improvement on converting subselect

Tom Lane wrote:

>Rajesh Kumar Mallah <mallah(at)trade-india(dot)com> writes:
>
>
>>explain analyze SELECT company_id , (SELECT edition FROM ONLY
>>public.branding_master b WHERE old_company_id = a.company_id OR company_id =
>>a.company_id ORDER BY b.company_id DESC LIMIT 1) from public.branding_master
>>a limit 50;
>>Total runtime: 19429.76 msec
>>
>>
>
>
>
>>CREATE FUNCTION most_recent_edition (integer) returns integer AS 'SELECT
>>edition::integer FROM ONLY public.branding_master b WHERE old_company_id = $1
>>OR company_id = $1 ORDER BY b.company_id DESC LIMIT 1 ' language 'sql';
>>
>>
>
>
>
>>tradein_clients=# explain analyze SELECT company_id ,
>>most_recent_edition(company_id) from public.branding_master limit 50;
>>Total runtime: 3969.52 msec
>>
>>
>
>Odd. Apparently the planner is picking a better plan in the function
>context than in the subselect context --- which is strange since it
>ought to have less information.
>
>AFAIK the only way to see the plan generated for a SQL function's query
>is like this:
>
>regression=# create function foo(int) returns int as
>regression-# 'select unique1 from tenk1 where unique1 = $1' language sql;
>CREATE FUNCTION
>regression=# set debug_print_plan TO 1;
>SET
>regression=# set client_min_messages TO debug;
>SET
>regression=# select foo(55);
>DEBUG: plan:
>DETAIL: {RESULT :startup_cost 0.00 :total_cost 0.01 :plan_rows 1 :plan_width 0
>:targetlist ({TARGETENTRY :resdom {RESDOM :resno 1 :restype 23 :restypmod -1
>:resname foo :ressortgroupref 0 :resorigtbl 0 :resorigcol 0 :resjunk false}
>:expr {FUNCEXPR :funcid 706101 :funcresulttype 23 :funcretset false
> ... (etc etc)
>
>Would you do that and send it along? I'm curious ...
>

Sorry for the delayed response.

tradein_clients=# explain analyze SELECT company_id ,
data_bank.most_recent_edition(company_id) from
public.branding_master limit 50;

--------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.00..3.57 rows=50 width=4) (actual
time=149.52..2179.49 rows=50 loops=1)
-> Seq Scan on branding_master (cost=0.00..6626.52 rows=92752
width=4) (actual time=149.51..2179.30 rows=51 loops=1)
tradein_clients=#
tradein_clients=#
tradein_clients=# explain analyze SELECT company_id ,
data_bank.most_recent_edition(company_id) from
public.branding_master limit 50;
DEBUG: StartTransactionCommand
LOG: plan:
{ LIMIT :startup_cost 0.00 :total_cost 185.65 :rows 1 :width 6
:qptargetlist
({ TARGETENTRY :resdom { RESDOM :resno 1 :restype 23 :restypmod -1
:resname
edition :reskey 0 :reskeyop 0 :ressortgroupref 0 :resjunk false }
:expr { EXPR
:typeOid 23 :opType func :oper { FUNC :funcid 313 :funcresulttype 23
:funcretset false :funcformat 1 } :args ({ VAR :varno 1 :varattno 31
:vartype
21 :vartypmod -1 :varlevelsup 0 :varnoold 1 :varoattno 31})}} {
TARGETENTRY
:resdom { RESDOM :resno 2 :restype 23 :restypmod -1 :resname company_id
:reskey 0 :reskeyop 0 :ressortgroupref 1 :resjunk true } :expr { VAR
:varno 1
:varattno 1 :vartype 23 :vartypmod -1 :varlevelsup 0 :varnoold 1
:varoattno
1}}) :qpqual <> :lefttree { INDEXSCAN :startup_cost 0.00 :total_cost
24302.69
:rows 131 :width 6 :qptargetlist ({ TARGETENTRY :resdom { RESDOM
:resno 1
:restype 23 :restypmod -1 :resname edition :reskey 0 :reskeyop 0
:ressortgroupref 0 :resjunk false } :expr { EXPR :typeOid 23
:opType func
:oper { FUNC :funcid 313 :funcresulttype 23 :funcretset false
:funcformat 1 }
:args ({ VAR :varno 1 :varattno 31 :vartype 21 :vartypmod -1
:varlevelsup 0
:varnoold 1 :varoattno 31})}} { TARGETENTRY :resdom { RESDOM :resno
2 :restype
23 :restypmod -1 :resname company_id :reskey 0 :reskeyop 0
:ressortgroupref 1
:resjunk true } :expr { VAR :varno 1 :varattno 1 :vartype 23
:vartypmod -1
:varlevelsup 0 :varnoold 1 :varoattno 1}}) :qpqual ({ EXPR :typeOid 16
:opType or :oper <> :args ({ EXPR :typeOid 16 :opType op :oper {
OPER :opno
96 :opid 65 :opresulttype 16 :opretset false } :args ({ VAR :varno 1
:varattno
19 :vartype 23 :vartypmod -1 :varlevelsup 0 :varnoold 1 :varoattno
19} {
PARAM :paramkind 12 :paramid 1 :paramname \<unnamed> :paramtype 23
})} { EXPR
:typeOid 16 :opType op :oper { OPER :opno 96 :opid 65 :opresulttype 16
:opretset false } :args ({ VAR :varno 1 :varattno 1 :vartype 23
:vartypmod -1
:varlevelsup 0 :varnoold 1 :varoattno 1} { PARAM :paramkind 12
:paramid 1
:paramname \<unnamed> :paramtype 23 })})}) :lefttree <> :righttree
<> :extprm
() :locprm () :initplan <> :nprm 0 :scanrelid 1 :indxid ( 310742439)
:indxqual (<>) :indxqualorig (<>) :indxorderdir -1 } :righttree <>
:extprm ()
:locprm () :initplan <> :nprm 0 :limitOffset <> :limitCount { CONST
:consttype 23 :constlen 4 :constbyval true :constisnull false
:constvalue 4 [
1 0 0 0 ] }}

DEBUG: CommitTransactionCommand

>
>
>
>>But i feel it can be lot more faster , can anyone suggest me something
>>to try.
>>
>>
>Create an index on old_company_id, perhaps.
>
Its there already..
branding_master_old_comapany_id btree (old_company_id),

regds , mallah.

>
> regards, tom lane
>
>---------------------------(end of broadcast)---------------------------
>TIP 2: you can get off all lists at once with the unregister command
> (send "unregister YourEmailAddressHere" to majordomo(at)postgresql(dot)org)
>
>