Nonrepeatable Reads and Phantom Reads

Guys, I am very confuse about the definitions of Nonrepeatable Reads and Phantom Reads when I read the BEA Documentaion in http://e-docs.bea.com/workshop/docs81/doc/en/wls/guide/advanced/EJBsAndTransactions.html
The definition was queit confusing to me because they seems to describe the same thing, but it is obviously not the same thing. The problem is to see the difference among then.
What is that difference? Could I have an practical example of that difference?
Thanks everyone

Non-Repeatable reads: When a row is updated in database. 2 reads may not return same data.
Phantom reads is where a new row is inserted into the database, hence the 2 selects may not return same set of data.
Chekc the link below for example queies. hope it helps.
http://en.wikipedia.org/wiki/Isolation_(computer_science)
#Phantom_Reads

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Dirty reads vs phantom reads

Hi,
What is the difference between a "Dirty Read" and "Phantom Reads". Can anyone explain in brief or give an example?
Thanks in advance.

A dirty read is an uncommitted read, which may or may not be exist in the table. A phantom is a ghost record that doesn't appear in a transaction initially but appears if it is read again because some other transaction has inserted rows matching the criteria.
Here are examples of both:
--Dirty read example
create table t1 (c1 int null, c2 varchar(50) null)
go
insert t1(c1, c2) values (1, 'one')
insert t1(c1, c2) values (2, 'two')
insert t1(c1, c2) values (3, 'three')
insert t1(c1, c2) values (4, 'four')
begin tran
update t1 set c2 = 'zero'
-- let this run in the current query window and open a new query window to run the below statement
--and you will see all 4 rows having a value of 0 in column c2, which is uncommitted data
select * from t1 with (nolock)
--uncomment this and run the below statement and rerun the above statement
--and you will see the previous values of one, two, three and four
--rollback tran
Here's an example of a phantom reads:
--Phantom example
create table t1 (c1 int null, c2 varchar(50) null)
go
insert t1(c1, c2) values (1, 'one')
insert t1(c1, c2) values (2, 'two')
insert t1(c1, c2) values (3, 'three')
insert t1(c1, c2) values (4, 'four')
-- let this run in the current first query window and open a second query window to run the below statement
--and you will see all 2 rows having a value in column c2 starting with character t
begin tran
select * from t1
where c2 like 't%'
--now insert the new value of ten (matching the query criteria - starts with t) from the first query window
insert t1(c1, c2) values (10, 'ten')
--Run the below statement again from the second query window that is open and you will see the new row
--that got inserted - so 3 rows are seen including the newly inserted ten
--this new row is a phantom read
select * from t1
where c2 like 't%'
--uncomment this and run the below statement in the second query window
--rollback tran
Satish Kartan www.sqlfood.com

What is the difference of public-read and public-read protected

I have noticed that the access of some variables in API document is public-read protected. I tried the following code. They seem all the same.
class FatherClass{
public-read var a;
public-read protected var b;
init{
    a=1;
    println(a);
    b=1;
    println(b);
class SubClass extends FatherClass{
    init{
        a=4;
        println(a);
        b=4;
        println(b);
var subClass=SubClass{};

As you see in my code, subclass can write the variable with either public-read and public-read protected. What write access do the public-read protected widen? That's because your subclass is in the same script as the variable. Move the subclass to a separate script and it would not be able to write when the access is public-read.
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"public-read protected" = any code can read, code in the same script, in the same package or in a subclass can write.

Find physical reads and logical reads ?

Hi,
how will find out physical reads and logical reads ?

Well I would suggest you read the report from statspack/awr.They as suggested by Amit,have a load profile section.That would be helpful for you in finding the details of this thing. Also which version you are? If you are in 10g than the EM is able to give you a compare period report where you can compare 2 different days's periods information and can check which particular part has changed.
In addition to this , look for the information of the metrics in the documentation.As the physical read and logical reads are statistics which are happening in the system.So from 10g onwards, oracle is keeping a track in the deflectionin the statistics. So if you see that than it willbe easy for you to manage and monitor it.
I shall try to findthe name of some views related to it and post.
Aman....

Difference between db file sequential read and scattered read

Hi,
Oracle Version : 10.2.0.1
Operating system: Linux
Can any one please help me what is the difference between db file sequential read and scattered read or please give any best related links .
Thanks & Regards,
Poorna Prasad.

>
A sequential read is a single-block read. Single block I/Os are usually the result of using indexes.
A db file scattered read issues a scattered read to read the data into multiple discontinuous memory locations. A scattered read is usually a multiblock read. It can occur for a fast full scan (of an index) in addition to a full table scan.
>
See Performance Tuning Guide:
http://download.oracle.com/docs/cd/B19306_01/server.102/b14211/instance_tune.htm#i20526
http://download.oracle.com/docs/cd/B19306_01/server.102/b14211/instance_tune.htm#i15958
Edited by: P. Forstmann on 20 oct. 2009 09:11

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Attachments:
Multicounter_Synchronization_App_Note.doc ‏55 KB

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Nonrepeatable Reads and Phantom Reads

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