Re: Duplicate Unique Key constraint error

Thanks alot for all your suggestions gentlemen.
I changed it to a SERIAL column and all the pain has been automatically
alleviated :)

Thanks a ton.
~Harpreet

On 7/10/07, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> "Harpreet Dhaliwal" <harpreet(dot)dhaliwal01(at)gmail(dot)com> writes:
> > Transaction 1 started, saw max(dig_id) = 30 and inserted new dig_id=31.
> > Now the time when Transaction 2 started and read max(dig_id) it was
> still 30
> > and by the time it tried to insert 31, 31 was already inserted by
> > Transaction 1 and hence the unique key constraint error.
>
> This is exactly why you're recommended to use sequences (ie serial
> columns) for generating IDs. Taking max()+1 does not work, unless
> you're willing to lock the whole table and throw away vast amounts of
> concurrency.
>
> regards, tom lane
>