Hiroshi Inoue <Inoue@tpf.co.jp> writes:
>>>> Postgres doesn't have an idea of what a 'top-level' statement is? I.E.
>>>> statement as submitted by a client (libpq)?
>>
>> There's never been any reason to make such a distinction.
> There's already a distinction.
> Snapshot is made per top-level statement and functions/subqueries
> use the same snapshot as that of top-level statement.
Not so. SetQuerySnapshot is executed per querytree, not per top-level
statement --- for example, if a rule generates multiple queries from
a user statement, SetQuerySnapshot is called again for each query.
With the current structure of pg_exec_query_string(), an operation
executed in the outer loop, rather than the inner, would more or less
correspond to one "top level" query --- if you want to assume that
pg_exec_query_string() is only called from PostgresMain. That's
true today but hasn't always been true --- I believe it used to be
used to parse SPI commands, and someday it may be again.
regards, tom lane
