On Tue, Feb 28, 2017 at 6:22 AM, David Steele <david@pgmasters.net> wrote:
>>> I'm not sure that's the case. It seems like it should lock just as
>>> multiple backends would now. One process would succeed and the others
>>> would error. Maybe I'm missing something?
>>
>> Hm, any errors happening in the workers would be reported to the
>> leader, meaning that even if one worker succeeded to run
>> pg_start_backup() it would be reported as an error at the end to the
>> client, no? By marking the exclusive function restricted we get sure
>> that it is just the leader that fails or succeeds.
>
> Good point, and it strengthens the argument beyond, "it just seems right."
I think the argument should be based on whether or not the function
depends on backend-private state that will not be synchronized.
That's the definition of what makes something parallel-restricted or
not.
It looks like pg_start_backup() and pg_stop_backup() depend on the
backend-private global variable nonexclusive_backup_running, so they
should be parallel-restricted.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
