Re: Question about isolation

Samuel Tardieu <sam@rfc1149.net> writes:
>>> Do I have the guarantee that, in any event, rows deleted from
>>> table t by the delete won't reappear in the select result?
>> 
>> i do not think you have that guarantee in READ COMMITTED mode
>> because there is a slight possibility another backend sneaked a
>> committed insert in between the delete and select
>> statement.

> Yes. But the possible effect your describe (insertion of new rows
> after the DELETE statement and before the SELECT) matches accurately
> the symptoms we are observing.

Hmm.  I think you need to look closer.  AFAIR the READ COMMITTED
behavior is only an issue if you give the commands interactively
from the client.  Inside a plpgsql function we do not do
SetQuerySnapshot() and therefore the snapshot of other transactions'
effects does not advance.  So I think the coding should be safe
... at the moment.  (A number of people think the lack of
SetQuerySnapshot inside functions is a bug; so the behavior might
change in future.)

Using SERIALIZABLE mode would probably make your code more future-proof,
but if you are presently seeing failures, there's some other effect
involved here.
        regards, tom lane