Oracle-L: RE: a quick SQL performance question

From: kkennedy <kkennedy_at_firstpoint.com>
Date: Thu, 18 Jul 2002 13:11:01 -0800
Message-ID: <F001.0049BF86.20020718131101@fatcity.com>

Hi Andrey,
If the volume of rows is not too great, you can use a technique I've used. Retrieve the rowids and store them in a PL/SQL table as you process them. At the end of the processing loop, use a forall loop to delete the rows using the PL/SQL table. I know a 2000 row PL/SQL table should be no problem. I'm not really sure if a 20000 row PL/SQL table presents a performance or memory problem. If it does, you could periodically issue the forall delete loop within the main processing loop. HTH
Kevin Kennedy
First Point Energy Corporation

-----Original Message-----
Sent: Thursday, July 18, 2002 12:36 PM
To: Multiple recipients of list ORACLE-L

Dear gurus !
I apologize for wasting your time.
I have had a second thought and realized that option (2) is not feasible, simply because i might "miss" some records, i.e. delete the records that are inserted into MYTAB DURING the execution of the cursor. I.e. , time will pass between the opening of the cursor (i.e. execution of the cursor's SELECT statement) and between the delete outside the cursor. Meanwhile , new records will get inserted , which are still unprocessed by the cursor's business logic.....
So , i must ensure that i delete only the "processed" records , i.e. i must delete inside the cursor's loop.
Right ?

-----Original Message-----
Sent: Thu, July 18, 2002 8:39 PM
To: Multiple recipients of list ORACLE-L

Dear all !
I've got a cursor , which selects approximately 25% of records in a table (the total number of records in that table is typically 2 to 20 thousands). For each record ,fetched in that cursor, i need to do some processing , and then delete that record.
Now, what's faster:
1) Add the rowid to the fields selected inside the cursor, and issue "delete from MYTAB where rowid = ...." , for each record inside the cursor. or
2) Leave the cursor intact, and just issue one delete statement afterwards, which will delete all the records , fetched by the cursor.

This operation is executed every couple of seconds, so i want to maximally optimize it .
Cheers.
I'd very much appreciate a prompt responce. Thanks a lot ~

DBAndrey

03-9254520
058-548133
mailto:andreyb_at_elrontelesoft.com

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Author: Andrey Bronfin
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Author: Andrey Bronfin
INET: andreyb_at_elrontelesoft.com

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RE: a quick SQL performance question - rethinked