This coding assumes the <literal>unique_violation</> error is caused by

the <command>INSERT</>, and not by, say, an <command>INSERT</> in a

trigger function on the table. More safety could be had by using the

trigger function on the table. It might also misbehave if there is

more than one unique index on the table, since it will retry the

operation regardless of which index caused the error.

More safety could be had by using the

features discussed next to check that the trapped error was the one

expected.

</para>