Re: does update table with identical values actually write to disk?
- From: Jared Still <jkstill@xxxxxxxxx>
- To: clay.colburn@xxxxxxxxx
- Date: Mon, 1 Nov 2010 11:44:01 -0700
On Mon, Nov 1, 2010 at 10:57 AM, Clay Colburn <clay.colburn@xxxxxxxxx>wrote:
> ... So for example if I have a row of data:
>
> create table my_test(id number, val varchar(10));
> insert into my_test(1, 'one');
>
> and I run the statement
>
> update my_test set val = 'one' where id = 1;
>
> will it write the new value to disk or evaluate that it is the same and
> skip the write?
>
>
Check your undo and redo stats before and after the transaction
and I think you will find your answer.
Here's a query to check the stats:
with chgstats as (
select
name.name name,
sum(stat.value) valuesum
from v$mystat stat, v$statname name
where
stat.statistic# = name.statistic#
and (name.name like 'redo%' or name.name like 'undo%')
group by name.name
order by name.name
)
select name, valuesum
from chgstats
where valuesum <> 0;
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist
Oracle Blog: http://jkstill.blogspot.com
Home Page: http://jaredstill.com
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