RE: How to project the time a delete will take
- From: "Hatzistavrou John" <John.Hatzistavrou.sema@xxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 30 Jan 2004 16:42:31 +0200
Dear Nelson,
Oracle release 8.1.7.4, solaris 8=20
The entries that will be deleted are ~ 200 million . The customer is
pushing for delete although we have pointed out that a partition will be
wiser (we are using truncate now). The customer asked us to prove that
the delete is not efficient although we have explained that there are a
number of issues such as redo and undo etc. There are 3 indexes defined
against the table.
I am doing the following experiment
a) get a reading from dbms_utility.get_time
b) execute a delete for a row
c) get a second reading from dbms_utility.get_time
d) Check the diff between a and c which is 732 centiceconds (if I
convert it well is 7,32 secs)
Kind Regards,
Hatzistavrou Yannis
-----Original Message-----
From: nelson.petersen@xxxxxxxxxxxxxxx
[mailto:nelson.petersen@xxxxxxxxxxxxxxx]=20
Sent: Friday, January 30, 2004 4:25 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: How to project the time a delete will take
Hi John (Yannis?),
Assumptions:
1. You are deleting from one table.
2. There are no referential constraint issues. (You have disabled or
dropped them.)
3. You are deleting 80% or more of the data from this table. =20
(Anything less makes my suggestion less appropriate.)
I don't have a way for you to estimate how long the delete will take.
I have a suggestion, though.
What version of Oracle are you running?
If you're on Oracle 8.1.5 or higher (I think EXPORT has the QUERY option
as
of 8.1.5)
you might consider the following:
EXPORT ... QUERY=3D"WHERE ..." file=3Ddata_to_be_left.dmp etc.
>>> The WHERE clause should select the data that you do *NOT* want to
delete.
Truncate the table.
IMPORT file=3Ddata_to_be_left.dmp ... etc.
This is a quick way to delete large amounts of data.
REDO generated by IMPORT might be less than that generated by DELETE.
As always, test on a test database before trusting this in production!
If you are on earlier versions of Oracle, there are ways to do something
similar
using CREATE TABLE AS SELECT * FROM table1 WHERE
data_col=3D'data_you_need_to_keep';
Of course, it all depends on how much data you need to save.
You don't say if this table has 101 million rows or 10,000 million rows.
HTH,
Nelson Petersen
Database Administrator
Home Hardware Stores Limited.
Nelson.Petersen@xxxxxxxxxxxxxxx
-----Original Message-----
From: Hatzistavrou John [mailto:John.Hatzistavrou.sema@xxxxxxxxxxxxxx]
Sent: Friday, January 30, 2004 7:48 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: How to project the time a delete will take
Dear All,
=20
Is there a formula that can give an estimation on how long a delete
operation will take on a tables to delete 100 million rows?
=20
Kind Regards,
=20
=20
Hatzistavrou Yannis
=20
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