Message-ID: <55CB2F54.5030103@2ndquadrant.fr>
Date: Wed, 12 Aug 2015 13:34:44 +0200
From: Vik Fearing <vik@2ndquadrant.fr>
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To: pgsql-performance@postgresql.org, robcampbell73@gmail.com
Subject: Re: Slow Query
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On 08/12/2015 04:34 AM, robbyc wrote:
> Hi,
> 
> I am new to optimizing queries and i'm getting a slow running time
> (~1.5secs) with the following SQL:

Before mucking about with work_mem and indexes, the first thing to do is
rewrite this query correctly.  Here are just some of the things wrong
with the query as written:

* You're doing a DISTINCT on the same set of columns also in a GROUP BY.
  This is redundant and causes needless deduplication.

* You're joining two GROUPed BY then DISTINCTed queries using the UNION
  operator which will do yet another pass for deduplication.

* You've got the entire query repeated for just a simple difference in
  the global WHERE clause.  These can be merged.

* You've kept LEFT JOINs in the subquery but you don't use any values
  from them.  These can be safely removed altogether.

* You're using a NOT IN clause which is almost never what you want.  Use
  NOT EXISTS instead.

What is this list() function?  How is it defined?  Can it be replaced
with string_agg()?

You're not doing yourself any favors at all with all this quoting and
mixed case stuff.

Here is a rewritten version, please let me know how it performs:

SELECT "Vacancy"."ID",
       "Vacancy"."JobTitle",
       "Vacancy"."DateCreated",
       "Vacancy"."CustomAccess",
       "Department"."Name" as "Department",
       list("Occupation"."Name") as "Occupation",
       "Vacancy"."PositionNo",
       "Vacancy"."Template"
FROM "Vacancy"
JOIN "CategoryOption_TableRow" as "c_50" ON (
        "c_50"."Category_TableID"= 50
    AND "c_50"."RowID" = "Vacancy"."ID"
    AND "c_50"."CategoryOptionID"=19205)
LEFT JOIN "CategoryOption_TableRow" as "c_22" ON (
        "c_22"."RowID" = "Vacancy"."ID"
    AND "c_22"."Category_TableID" = 22)
LEFT JOIN "CategoryOption" as "Occupation" ON (
        "Occupation"."ID" = "c_22"."CategoryOptionID")
LEFT JOIN "TableRow_TableRow" as "t_33" ON (
        "t_33"."Table1RowID" = "Vacancy"."ID"
    AND "t_33"."Table_TableID" = 33)
LEFT JOIN "Department" ON (
        "Department"."ID" = "t_33"."Table2RowID"
    AND "Department"."Active" = 't'
    AND "Department"."ClientID" = 263)
WHERE "Vacancy"."ClientID" = 263
  AND NOT EXISTS (
        SELECT 1
        FROM "Vacancy" as _Vacancy
        JOIN "CategoryOption_TableRow" "ct126" on (
                "ct126"."Category_TableID" = 126
            AND "RowID" = _Vacancy."ID")
        WHERE _Vacancy."Template"
          AND "ct126"."CategoryOptionID" IN (34024,35254,35255,35256)
          AND _Vacancy."ID" = "Vacancy"."ID")
  AND ("Vacancy"."Template" = 't' OR "Vacancy"."Level" = 1)
GROUP BY "Vacancy"."ID", "Vacancy"."JobTitle", "Vacancy"."DateCreated",
         "Vacancy"."CustomAccess", "Department"."Name",
         "Vacancy"."PositionNo", "Vacancy"."Template"


> SELECT distinct("Vacancy"."ID"), "Vacancy"."JobTitle",
> "Vacancy"."DateCreated", "Vacancy"."CustomAccess"
> , "Department"."Name" as "Department", list("Occupation"."Name") as
> "Occupation", "Vacancy"."PositionNo"
> , "Vacancy"."Template" from 
>    "Vacancy"
> LEFT JOIN "CategoryOption_TableRow" as "c_22" 
>          ON ("c_22"."RowID" = "Vacancy"."ID" 
>          and "c_22"."Category_TableID" = 22)
> LEFT JOIN "CategoryOption" as "Occupation"
>          ON ("Occupation"."ID" = "c_22"."CategoryOptionID")
> LEFT JOIN "TableRow_TableRow" as "t_33" 
>       ON ("t_33"."Table1RowID" = "Vacancy"."ID" 
>       and "t_33"."Table_TableID" = 33 )
> LEFT JOIN "Department"
>          ON ("Department"."ID" = "t_33"."Table2RowID" and
> "Department"."Active" = 't' and "Department"
> ."ClientID" = 263)
> JOIN "CategoryOption_TableRow" as "c_50" ON ("c_50"."Category_TableID"= 50
> and "c_50"."RowID" = "Vacancy"
> ."ID" and "c_50"."CategoryOptionID"=19205)
> WHERE "Vacancy"."ClientID" = 263 AND "Vacancy"."ID" NOT IN(SELECT
> DISTINCT("Vacancy"."ID") 
>             FROM "Vacancy" join "CategoryOption_TableRow" "ct126" on
> ("ct126"."Category_TableID" = 126
>  and "RowID" = "Vacancy"."ID") 
>             left join "Workflow" on ("Workflow"."VacancyID" = "Vacancy"."ID"
> and "Workflow"."Level" 
> = 1) 
>             left join "CategoryOption_TableRow" "c30" on ("c30"."RowID" =
> "Workflow"."ID" and "c30"."Category_TableID"
>  = 30 and "c30"."CategoryOptionID" = 21923) 
>             WHERE "Template" AND "ct126"."CategoryOptionID"
> IN(34024,35254,35255,35256)) and "Vacancy"
> ."Template" = 't'
> GROUP BY "Vacancy"."ID", "Vacancy"."JobTitle", "Vacancy"."DateCreated",
> "Vacancy"."CustomAccess", "Department"
> ."Name", "Vacancy"."PositionNo", "Vacancy"."Template"
> UNION
> SELECT distinct("Vacancy"."ID"), "Vacancy"."JobTitle",
> "Vacancy"."DateCreated", "Vacancy"."CustomAccess"
> , "Department"."Name" as "Department", list("Occupation"."Name") as
> "Occupation", "Vacancy"."PositionNo"
> , "Vacancy"."Template" from 
>    "Vacancy"
> LEFT JOIN "CategoryOption_TableRow" as "c_22" 
>          ON ("c_22"."RowID" = "Vacancy"."ID" 
>          and "c_22"."Category_TableID" = 22)
> LEFT JOIN "CategoryOption" as "Occupation"
>          ON ("Occupation"."ID" = "c_22"."CategoryOptionID")
> LEFT JOIN "TableRow_TableRow" as "t_33" 
>       ON ("t_33"."Table1RowID" = "Vacancy"."ID" 
>       and "t_33"."Table_TableID" = 33 )
> LEFT JOIN "Department"
>          ON ("Department"."ID" = "t_33"."Table2RowID" and
> "Department"."Active" = 't' and "Department"
> ."ClientID" = 263)
> JOIN "CategoryOption_TableRow" as "c_50" ON ("c_50"."Category_TableID"= 50
> and "c_50"."RowID" = "Vacancy"
> ."ID" and "c_50"."CategoryOptionID"=19205)
> WHERE "Vacancy"."ClientID" = 263 AND "Vacancy"."ID" NOT IN(SELECT
> DISTINCT("Vacancy"."ID") 
>             FROM "Vacancy" join "CategoryOption_TableRow" "ct126" on
> ("ct126"."Category_TableID" = 126
>  and "RowID" = "Vacancy"."ID") 
>             left join "Workflow" on ("Workflow"."VacancyID" = "Vacancy"."ID"
> and "Workflow"."Level" 
> = 1) 
>             left join "CategoryOption_TableRow" "c30" on ("c30"."RowID" =
> "Workflow"."ID" and "c30"."Category_TableID"
>  = 30 and "c30"."CategoryOptionID" = 21923) 
>             WHERE "Template" AND "ct126"."CategoryOptionID"
> IN(34024,35254,35255,35256))  and "Vacancy"
> ."Template" <> 't' AND "Vacancy"."Level" = 1 
> GROUP BY "Vacancy"."ID", "Vacancy"."JobTitle", "Vacancy"."DateCreated",
> "Vacancy"."CustomAccess", "Department"
> ."Name", "Vacancy"."PositionNo", "Vacancy"."Template"
>  ORDER BY "JobTitle"
> 
> Running explain analyze gives me the following information: 
> http://explain.depesz.com/s/pdC <http://explain.depesz.com/s/pdC>  
> 
> For a total runtime: 2877.157 ms
> 
> If i remove the left joins on Department and TableRow_TableRow this reduces
> the run time by about a third.
> Additionally removing CategoryOption and CategoryOption_TableRow joins
> further reduces by a about a third.
> 
> Given that i need both these joins for the information retrieved by them,
> what would be the best way to re-factor this query so it runs faster?
> 
> Looking at the output of explain analyze the hash aggregates and sort seem
> to be the primary issue.
> 
> Thanks in advance  


-- 
Vik Fearing                                          +33 6 46 75 15 36
http://2ndQuadrant.fr     PostgreSQL : Expertise, Formation et Support


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