Re: A transaction question

Christoph Rupp wrote:

> Hi,
>
> i have a question about two parallel transactions which insert the
> same key.
>
> Assume that key A does not yet exist.
>
> T1 Begin
> T2 Begin
> T1 Insert A
> T2 Insert A
> T1 Commit
> T2 Commit
>
> My guess is: "T2 Insert A" is a conflict with the previous insert of
> T1. But i also think that in a MVCC database the conflict can only be
> resolved when T2 is committed. What happens then? Does the commit
> fail, or is A silently overwritten? Or is the typical behaviour in
> this case implementation-specific?
>
> Thanks for your answers,
> Christoph

Even in MVCC, T2's Insert A will block until after T1 Commit.

| T1 | T2 |

| Begin  |        |
|        | Begin  |
| Ins A  |        |
|        | Ins A  |
|        | (block)|
| Commit | (fail) |