Fidel Viegas wrote:

> On Fri, Feb 29, 2008 at 10:33 AM, Eugen Stoianovici
> <eugen.stoianovici@...> wrote:
>
>
>> How does firebird's versioning work on transactions? If i have..let's
>> say a stocks application. At some point there are 10 items A in stock
>> Users U1 and U2 both sell 8 A's roughly at the same time:
>>
>> 1. --U1 : begin transaction--
>> 2. --U2 : begin transaction--
>>
>> 3. U1: Insert some sale info into sale table
>> 4. U1: Check if there are 8 A's available (true at this poing)
>> 5. U2: Insert some sale info into sale table
>> 6. U1: Update stock for A to stockA-8 items available
>> 7. U2: Check if there are 8 A'2 available (also true at this point?)
>> 8. --U1: Commit transaction--
>> 9. U2: Update stock for A to stockA-8 items available (which would set
>> stock for A at -6)
>> 10 --U2: commits--(does firebird accept this transaction?)
>>
>> From what i understood reading the docs, U2 (the second transaction)
>> doesn't see what U1 does until U2 commits. Am i right? How does firebird
>> handle this issue? How should i handle this issue?
>>
>
> Hi Eugen,
>
> Firebird uses Multi Version Concurrency control. Have a look here
> http://www.firebirdsql.org/doc/whitepapers/fb_vs_ibm_vs_oracle.htm for
> a better understading on how that works.
>
> All the best,
>
> Fidel.
>

Thank you, that was exactly what i was looking for. MVCC rules :)