cliff@krumvieda.com writes:
> suppose a table has a UNIQUE constraint on a column, and two
> concurrent transactions attempt to INSERT a row with the same value
> for that column:
Whichever one manages to get to the index page first will go through.
The second one will block waiting to see if the first one commits,
and will error out if so --- or proceed, if it aborts.
regards, tom lane