Re: execution plan : Oracle vs PostgreSQL

here is the EXPLAIN ANALYSE of my query :

{SORT
:startup_cost 9.65
:total_cost 9.66
:plan_rows 1
:plan_width 28
:targetlist (
{TARGETENTRY
:expr
{VAR
:varno 1
:varattno 1
:vartype 23
:vartypmod -1
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:varnoold 1
:varoattno 1
}
:resno 1
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:ressortgroupref 0
:resorigtbl 34719
:resorigcol 1
:resjunk false
}
{TARGETENTRY
:expr
{VAR
:varno 1
:varattno 2
:vartype 23
:vartypmod -1
:varlevelsup 0
:varnoold 1
:varoattno 2
}
:resno 2
:resname evolution
:ressortgroupref 1
:resorigtbl 34719
:resorigcol 2
:resjunk false
}
{TARGETENTRY
:expr
{VAR
:varno 1
:varattno 3
:vartype 23
:vartypmod -1
:varlevelsup 0
:varnoold 1
:varoattno 3
}
:resno 3
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:ressortgroupref 0
:resorigtbl 34719
:resorigcol 3
:resjunk false
}
{TARGETENTRY
:expr
{VAR
:varno 1
:varattno 4
:vartype 23
:vartypmod -1
:varlevelsup 0
:varnoold 1
:varoattno 4
}
:resno 4
:resname child_class
:ressortgroupref 0
:resorigtbl 34719
:resorigcol 4
:resjunk false
}
{TARGETENTRY
:expr
{VAR
:varno 1
:varattno 5
:vartype 23
:vartypmod -1
:varlevelsup 0
:varnoold 1
:varoattno 5
}
:resno 5
:resname indx
:ressortgroupref 2
:resorigtbl 34719
:resorigcol 5
:resjunk false
}
{TARGETENTRY
:expr
{VAR
:varno 1
:varattno 6
:vartype 23
:vartypmod -1
:varlevelsup 0
:varnoold 1
:varoattno 6
}
:resno 6
:resname ele_id
:ressortgroupref 0
:resorigtbl 34719
:resorigcol 6
:resjunk false
}
{TARGETENTRY
:expr
{VAR
:varno 1
:varattno 7
:vartype 23
:vartypmod -1
:varlevelsup 0
:varnoold 1
:varoattno 7
}
:resno 7
:resname doc_id
:ressortgroupref 0
:resorigtbl 34719
:resorigcol 7
:resjunk false
}
)
:qual <>
:lefttree
{INDEXSCAN
:startup_cost 0.00
:total_cost 9.64
:plan_rows 1
:plan_width 28
:targetlist (
{TARGETENTRY
:expr
{VAR
:varno 1
:varattno 1
:vartype 23
:vartypmod -1
:varlevelsup 0
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:varoattno 1
}
:resno 1
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:ressortgroupref 0
:resorigtbl 34719
:resorigcol 1
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{TARGETENTRY
:expr
{VAR
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:resno 2
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:ressortgroupref 1
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{TARGETENTRY
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{VAR
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{TARGETENTRY
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{VAR
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{TARGETENTRY
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{VAR
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:resorigcol 5
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{TARGETENTRY
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{VAR
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{TARGETENTRY
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:resno 7
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}
)
:qual (
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:opretset false
:args (
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{SUBPLAN
:subLinkType 4
:useOr false
:exprs <>
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{AGG
:startup_cost 4.93
:total_cost 4.94
:plan_rows 1
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{AGGREF
:aggfnoid 2116
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:resno 1
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{INDEXSCAN
:startup_cost 0.00
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:expr
{VAR
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{TARGETENTRY
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:resno 5
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{TARGETENTRY
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:resno 6
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{TARGETENTRY
:expr
{VAR
:varno 1
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:resno 7
:resname <>
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:resorigtbl 0
:resorigcol 0
:resjunk false
}
)
:qual (
{OPEXPR
:opno 96
:opfuncid 65
:opresulttype 16
:opretset false
:args (
{VAR
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}
{PARAM
:paramkind 15
:paramid 3
:paramname <>
:paramtype 23
}
)
}
)
:lefttree <>
:righttree <>
:initPlan <>
:extParam (b 0 1 2 3)
:allParam (b 0 1 2 3)
:nParamExec 0
:scanrelid 1
:indexid 34737
:indexqual (
{OPEXPR
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{PARAM
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{OPEXPR
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{OPEXPR
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{CONST
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:constvalue 4 [ 0 0 0 0 ]
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{OPEXPR
:opno 96
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{VAR
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{PARAM
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)
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)
:indexqualorig (
{OPEXPR
:opno 96
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:opretset false
:args (
{VAR
:varno 1
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:vartypmod -1
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{PARAM
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)
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{OPEXPR
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)
}
{OPEXPR
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{CONST
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:constlen 4
:constbyval true
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:constvalue 4 [ 0 0 0 0 ]
}
)
}
{OPEXPR
:opno 96
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:opresulttype 16
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:args (
{VAR
:varno 1
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:varoattno 1
}
{PARAM
:paramkind 15
:paramid 2
:paramname <>
:paramtype 23
}
)
}
)
:indexstrategy (i 3 3 2 3)
:indexsubtype (o 0 0 0 0)
:indexorderdir 1
}
:righttree <>
:initPlan <>
:extParam (b 0 1 2 3)
:allParam (b 0 1 2 3)
:nParamExec 0
:aggstrategy 0
:numCols 0
:numGroups 0
}
:plan_id 1
:rtable (
{RTE
:alias
{ALIAS
:aliasname c2
:colnames <>
}
:eref
{ALIAS
:aliasname c2
:colnames ("child_id" "evolution" "isremoved" "child_class"
"indx" "ele_id" "doc_id")
}
:rtekind 0
:relid 34719
:inh false
:inFromCl true
:requiredPerms 2
:checkAsUser 0
}
)
:useHashTable false
:unknownEqFalse false
:setParam <>
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)
}
)
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{OPEXPR
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}
)
}
)
:indexqualorig (
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:opresulttype 16
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{CONST
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}
{OPEXPR
:opno 96
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}
{OPEXPR
:opno 96
:opfuncid 65
:opresulttype 16
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:args (
{VAR
:varno 1
:varattno 3
:vartype 23
:vartypmod -1
:varlevelsup 0
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}
{CONST
:consttype 23
:constlen 4
:constbyval true
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:constvalue 4 [ 0 0 0 0 ]
}
)
}
)
:indexstrategy (i 3 3 3)
:indexsubtype (o 0 0 0)
:indexorderdir 1
}
:righttree <>
:initPlan <>
:extParam (b)
:allParam (b)
:nParamExec 4
:numCols 2
:sortColIdx 2 5
:sortOperators 97 97
}

Sort (cost=9.65..9.66 rows=1 width=28) (actual time=0.190..0.191 rows=1 loops=1)
Sort Key: evolution, indx
-> Index Scan using index_xdb_child on xdb_child c1 (cost=0.00..9.64 rows=1 width=28) (actual time=0.156..0.159 rows=1 loops=1)
Index Cond: ((doc_id = 100) AND (ele_id = 2589) AND (isremoved = 0))
Filter: (evolution = (subplan))
SubPlan
-> Aggregate (cost=4.93..4.94 rows=1 width=4) (actual time=0.053..0.053 rows=1 loops=1)
-> Index Scan using index_xdb_child on xdb_child c2 (cost=0.00..4.93 rows=1 width=4) (actual time=0.026..0.034 rows=1 loops=1)
Index Cond: ((doc_id = $0) AND (ele_id = $1) AND (evolution <= 0) AND (child_id = $2))
Filter: (child_class = $3)
Total runtime: 0.483 ms

-----Message d'origine-----
De : pgsql-general-owner(at)postgresql(dot)org
[mailto:pgsql-general-owner(at)postgresql(dot)org]De la part de FERREIRA,
William (VALTECH)
Envoyé : mardi 24 janvier 2006 11:34
À : pgsql-general(at)postgresql(dot)org
Objet : [GENERAL] execution plan : Oracle vs PostgreSQL

hi,

i have a database storing XML documents.
The main table contains the nodes of the document, the other tables contain data for each node (depending on the node's type : ELE, Text, PI, ...)

My test document has 115000 nodes.
the export of the document(extracting all informations from database and writing XML file on disk) takes 30s with Oracle and 5mn with Postgresql.
The tests have been made on different systems
- Sun systems :
- solaris8 : 16 cpu and 64Gb RAM
- solaris8 : 2cpu and 8Gb RAM
- Windows Systems :
- WinNT : 1 cpu(PIV) and 1Gb RAM
- WinXP : 1 cpu(centrino) and 512 RAM

the times are always the same, except with the centrino for which it takes 1 min.

So i don't understand such differences.

here is my main query (on the main table for getting the children of a node) and the execution plan for PostgreSQL and Oracle :

-Query :
SELECT *
FROM xdb_child c1
WHERE c1.doc_id = 100
AND c1.ele_id = 2589
AND c1.isremoved = 0
AND c1.evolution =
(SELECT
MAX (evolution)
FROM xdb_child c2
WHERE c2.doc_id = c1.doc_id
AND c2.ele_id = c1.ele_id
AND c2.evolution <= 0
AND c2.child_id = c1.child_id
AND c2.child_class = c1.child_class) ORDER BY c1.evolution, c1.indx

-Postgresql plan :
"Sort (cost=33.19..33.20 rows=1 width=28)"
" Sort Key: evolution, indx"
" -> Index Scan using index_xdb_child_1 on xdb_child c1 (cost=0.00..33.18 rows=1 width=28)"
" Index Cond: ((ele_id = 2589) AND (doc_id = 100) AND (isremoved = 0))"
" Filter: (evolution = (subplan))"
" SubPlan"
" -> Result (cost=4.34..4.35 rows=1 width=0)"
" InitPlan"
" -> Limit (cost=0.00..4.34 rows=1 width=4)"
" -> Index Scan Backward using index_xdb_child_2 on xdb_child c2 (cost=0.00..4.34 rows=1 width=4)"
" Index Cond: ((ele_id = $1) AND (doc_id = $0) AND (child_id = $2) AND (child_class = $3) AND (evolution <= 0))"
" Filter: (evolution IS NOT NULL)"

-Oracle plan (cost 14):
Operation Object Name Rows Bytes Cost Object Node In/Out PStart PStop

SELECT STATEMENT Optimizer Mode=CHOOSE 1 14
SORT ORDER BY 1 4 K 14
TABLE ACCESS BY INDEX ROWID XDB_CHILD 1 4 K 4
INDEX RANGE SCAN INDEX_XDB_CHILD_1 1 3
SORT AGGREGATE 1 65
FIRST ROW 1 65 3
INDEX RANGE SCAN (MIN/MAX) INDEX_XDB_CHILD_2 8 M 3

Regards

William

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