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From: John B. Matthews on 20 Jun 2010 12:13
In article
<06003d05-1f68-4c60-844a-f93bad0e6e81(a)s4g2000prh.googlegroups.com>,
gk <srcjnu(a)gmail.com> wrote:

> On Jun 20, 10:34 am, Lew <no...(a)lewscanon.com> wrote:
> > gk wrote:
> >
> > > where is the key difference(if any) ?
> >
> > Phantom read is a different number of rows returned from the query.
>
> True. because in the example they are using "INSERT" in transaction
> 2. surprisingly, Phantom read also called "REPEATABLE READ".

No, phantom read is a potential problem at the REPEATABLE READ
isolation level when a query contains a range in the WHERE clause, e.g.
"BETWEEN 10 AND 30". [1]

> Is it because they are not MODIFYING the values but adding some extra
> records into it i.e it repeates the values with some additional
> records.

No, "This can occur when range locks are not acquired on performing a
SELECT." [2]

> > Non-repeatable read is different values returned for a given row.
>
> True. because in the example they are using "UPDATE" in transaction
> 2. However,both of them are showing faulty results at the end of
> Transaction 1.

At the READ COMMITTED isolation level, "non-repeatable reads may occur
in a lock-based concurrency control method when read locks are not
acquired when performing a SELECT." [4]

The broken link from [3] to [4] has been repaired.

[1]<http://en.wikipedia.org/wiki/Isolation_(database_systems)#REPEATABLE_READ>
[2]<http://en.wikipedia.org/wiki/Isolation_(database_systems)#Repeatable_reads_.28phantom_reads.29>
[3]<http://en.wikipedia.org/wiki/Isolation_(database_systems)#READ_COMMITTED>
[4]<http://en.wikipedia.org/wiki/Isolation_(computer_science)#Read_Committed_.28Non-repeatable_reads.29>

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