Re: snapshots

Kovacs Baldvin <kb136@hszk.bme.hu> writes:
> Could somebody explain me the mechanism in the backend,
> which is responsible for the followings. (I tried to
> look around snapshots, but couldnt figure out th answer).

> In a transaction, isol. read comitted, a select from a
> table can see the comitted changes by others, but
> a previously declared cursor can not.

Yup.  The snapshot used for a particular query is nailed down when
ExecutorStart() is called.  Look around for uses of QuerySnapshot
and estate->es_snapshot.
        regards, tom lane