On 27 mai, 01:17, Sebastian Noack <[EMAIL PROTECTED]>
wrote:
[snip]
> Even if it is done by many parallel connections, because of
> transactions are managed by the DBMS too and ensure atomicity,
> consistency, isolation and durability of each transaction
>
[snip]
The problem is that DBMS don't use the same default isolation level.
Many DBMS use a read committed default, some a repeatable read and
very few a serializable level.
Some DBMS are even unable to support serializable.
The "for update" clause generally implied a repeatable read.
Read committed allow another transaction to update a record previously
read by your transaction.
Repeatable read allow phantom which mean that if you redo a select new
records can appear.
For more information on isoloation level you can read
http://en.wikipedia.org/wiki/Isolation_(computer_science)
JF
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