From: Frank Bax <fbax@sympatico.ca>
To: Peter T. Brown <peter@memeticsystems.com>
To: pgsql-sql@postgresql.org
Subject: Re: how can I improve the speed of this query
Date: Tue, 19 Nov 2002 10:44:07 -0500
Message-ID: <5.1.1.6.0.20021119103819.02fe48e0@pop6.sympatico.ca> (raw)
In-Reply-To: <1037392411.2473.36.camel@localhost.localdomain>
References: <web-1827592@davinci.ethosmedia.com>
<web-1827592@davinci.ethosmedia.com>
Problem could be the SeqScan on visitor (very last line of explain). This
appears to be coming from the last join in your query. Does an index on ID
exist on Visitor table?
Does changing:
WHERE "VisitorExtra"."ID"="Visitor"."ID" AND
"VisitorExtra"."ID"= 325903;
to
WHERE "VisitorExtra"."ID"="Visitor"."ID" AND
"Visitor"."ID"= 325903;
have any effect?
Why do you use "From VisitorExtra" in first select when no result fields
are in the table? Why not replace all references to "VisitorExtra"."ID"to
"Visitor"."ID"?
Frank
At 03:33 PM 11/15/02, Peter T. Brown wrote:
>Hi--
>
>I have this rather long complex query that takes really long to complete
>(please see below). It seems like I ought to improve the speed somehow.
>I don't understand, for example, what the query planner is doing when it
>says "Hash" and why this appears to take so long. And since I have a key
>for Visitor.ID, I don't understand why its doing a sequential scan on
>that table...
>
>Any advice would be greatly appreciated!
>
>
>Thanks
>
>Peter
>
>
>
>
>EXPLAIN SELECT
> "Visitor"."Created",
> "Visitor"."Updated",
> "Tidbit"."ID",
> "ProgramEvent"."ID",
> "Visitor"."Email",
> "Interest"."ID",
> "VisitorInternetDeviceAssoc"."ID",
> "Referral"."ID"
>
>FROM "VisitorExtra"
>
>LEFT OUTER JOIN Tidbit" ON
> "VisitorExtra"."ID"="Tidbit"."VisitorID"
>
>LEFT OUTER JOIN "ProgramEvent" ON
> "VisitorExtra"."ID"="ProgramEvent"."VisitorID"
>
>LEFT OUTER JOIN "Interest" ON
> "VisitorExtra"."ID"="Interest"."VisitorID"
>
>LEFT OUTER JOIN "VisitorInternetDeviceAssoc" ON
> "VisitorExtra"."ID"="VisitorInternetDeviceAssoc"."VisitorID"
>
>LEFT OUTER JOIN "Referral" ON
> "VisitorExtra"."ID"="Referral"."FromVisitorID","Visitor"
>
>WHERE "VisitorExtra"."ID"="Visitor"."ID" AND
> "VisitorExtra"."ID"= 325903;
>
>
>NOTICE: QUERY PLAN:
>
>Hash Join (cost=14584.37..59037.79 rows=57747 width=76)
> -> Merge Join (cost=0.00..36732.65 rows=57747 width=44)
> -> Merge Join (cost=0.00..29178.16 rows=10681 width=36)
> -> Nested Loop (cost=0.00..10505.74 rows=6674 width=28)
> -> Nested Loop (cost=0.00..435.29 rows=177
> width=20)
> -> Nested Loop (cost=0.00..15.70 rows=55
> width=12)
> -> Index Scan using VisitorExtra_pkey
> on VisitorExtra (cost=0.00..3.01
> rows=1 width=4)
> -> Index Scan
> using
>Tidbit_VisitorID_key on
>Tidbit (cost=0.00..12.67 rows=2
>width=8)
> -> Index Scan
> using
>ProgramEvent_VisitorID_key on
>ProgramEvent (cost=0.00..7.57
>rows=2 width=8)
> -> Index Scan using Interest_VisitorID_key on
> Interest (cost=0.00..56.66 rows=19 width=8)
> -> Index Scan using VisitorInternetDeviceAssoc_Visi on
> VisitorInternetDeviceAssoc (cost=0.00..16402.90
> rows=174887
>width=8)
> -> Index Scan using Referral_FromVisitorID_key on Referral
> (cost=0.00..6323.41 rows=87806 width=8)
> -> Hash (cost=6061.79..6061.79 rows=317379 width=32)
> -> Seq Scan on Visitor (cost=0.00..6061.79 rows=317379
>width=32)
>
>
>
>---------------------------(end of broadcast)---------------------------
>TIP 6: Have you searched our list archives?
>
>http://archives.postgresql.org
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To: pgsql-sql@postgresql.org
Cc: fbax@sympatico.ca, peter@memeticsystems.com
Subject: Re: how can I improve the speed of this query
In-Reply-To: <5.1.1.6.0.20021119103819.02fe48e0@pop6.sympatico.ca>
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