Re: Index question

From: Teresita Castro <Teresita.Castro_at_s-martmx.com>
Date: Wed, 25 Jun 2003 18:26:58 -0700
Message-ID: <F001.005B9FA8.20030625180418@fatcity.com>

Hi!!

Let explain more about my
situation.
The company that I work for is a chain
of stores around some city's on Mexico, they bought Lawson a system that uses Oracle to manage the data bases, at first they use SQL Server 2000, but I wasn't enough to manager all the information.
The structure of the table is all ready done and I have to learn it to do some reports that Lawson don't have, change or delete information and export some information to dbf files. Because we was using SQL Server I used Store procedures to return the select result to VB recordset and the I pass the select result to Crystal Report or to a DBF file.
Well I see that in Oracle the store
procedure do not returns the result set has easy has SQL Server so I use and statement that after execute it returns me the result in a record set.

sQuery = "SELECT COMPANY,LOCATION,
R_NAME FROM ICLOCATION " &
_ "WHERE COMPANY=2000 OR
COMPANY=2001 OR COMPANY=2002 order by COMPANY,LOCATION"Set recRS = New ADODB.RecordsetrecRS.Open sQuery, gcnOracle, adOpenForwardOnly, adLockReadOnly, adCmdText

or execute a delete or update
statement

sSQL = "update /*+ INDEX(itemloc
ITLSET2) */ itemloc set average_cost =" & costo & " where (company='2000') and item= '" & Arti & "'"gcnOracle.Execute sSQL
gcnOracle.Execute "Commit",
dbSQLPassThrough
Back to my problem:
In this case the update of the average cost has to be done on the table Item location ( ITEMLOC) that have all the item that each location( store) have. The locations have a company, when we changes the average cost is per company ( each company represent a different city)

So my boss execute the update
statement

sSQL = "update itemloc set
average_cost =" & costo & " where (company='2000') and item= '" & Arti & "'"
and she told me that per item it
takes like 10 seconds.
After read the article that I mention
she changes the statement to this :
sSQL = "update /*+

INDEX(itemloc ITLSET2) */ itemloc set average_cost =" & costo & " where (company='2000') and item= '" & Arti & "'"

ITLSET2 is a index that have company(1), location(2) and Item(3) and it takes 2 seconds per item, so that is way she is convinced that we have to uses the /*+ INDEX(itemloc ITLSET2) */ in all of our select, update or delete statement.

I hope you undestant my English and my problem too, because I have to do some really complicated queries that have like 3 or 5 tables in them, and using this method will give me some serious complications, maybe in this case (change of the average cost) is not too dangerous.
But I have to give her strong statements to change her mind.

Thanks for everything
friends!!
>>> [EMAIL PROTECTED] 06/25/03 06:10PM
>>>Teresita,I don't fully understand whether adding or removing a hint caused theproblem but like Stephane said - you should probably stay away from themfor now. If adding a hint decreased performance then you have proved thisfor yourself.A couple of important points:* Using an index isn't always faster than scanning the table* If a database is correctly analyzed then the optimisor can determine whento use indexes or not automatically* Hints can force the optimisor to choose a non-optimal execution plan. Ifyou are smarter than the optimisor this may be fine but in most cases theoptimisor will make the right decision when all tables are analyzed* Hints have very specific formatting and object name rules. If you renamean index the hint will become invalid and be blissfully ignored - you won'teven know.* There are some hints which can safely be used but it takes a goodunderstanding of Oracle first. My advice would be don't use them. If youhave a specific problem then post lot's of details here and someone mightsuggest trying a hint.* Until you really understand the implications of using a specific hint itcan be dangerous in terms of performance - Stephane is not lying when hesays you can do more harm than good. I have many cases where I can "tune"a query simply by removing the hints which someone included and lettingOracle do what it does

best.Regards,      
Mark.                                                                                                                                        


                      

"Teresita 
Castro"

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martmx.com>                
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om

26/06/2003

09:29

Please respond

Ophss...I have a terrible problem, I am using VB with Oracle and since weput that instruccion on the execute instruction our execution timedecrease.The problem is that my boss was the one that found that instruction and Ihave to told her not to uses it, but with her I have to show some evidencethat show why now to uses hits.Do you have any information that I can show to her.Thanks!!!>>> [EMAIL PROTECTED] 06/25/03 02:34PM
>>>Teresita, Since you advertise yourself as a newbie, listen to an old-timer :for the next two years, forget about hints. You risk doing more harmthan good.--Regards,Stephane FaroultOriole Software--Please see the official ORACLE-L FAQ: <A href="http://www.orafaq.net">http://www.orafaq.net--Author: Stephane Faroult INET: [EMAIL PROTECTED]Fat City Network Services -- 858-538-5051 <A
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