Re: Remove vacuum_defer_cleanup_age

On Wed, Oct 19, 2016 at 8:47 AM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> On Wed, Oct 19, 2016 at 08:33:20AM -0400, Robert Haas wrote:
>> On Tue, Oct 18, 2016 at 4:33 PM, Josh Berkus <josh(at)agliodbs(dot)com> wrote:
>> > Based on that argument, we would never be able to remove any
>> > configuration parameter ever.
>>
>> Well... no. Based on that argument, we should only remove
>> configuration parameters if we're fairly certain that they are not
>> useful any more, which will be rare, but is not never. I agree that
>> *if* vacuum_defer_cleanup_age is no longer useful, it should be
>> removed. I'm just not convinced that it's truly obsolete, and you
>> haven't really offered much of an argument for that proposition. It
>> does something sufficiently different from hot_standby_feedback that
>> I'm not sure it's accurate to say that one can substitute for the
>> other, and indeed, I see Andres has already suggested some scenarios
>> where it could still be useful.
>>
>> Actually, I think vacuum_defer_cleanup_age is, and always has been, an
>> ugly hack. But for some people it may be the ugly hack that is
>> letting them continue to use PostgreSQL.
>
> I see vacuum_defer_cleanup_age as old_snapshot_threshold for standby
> servers --- it cancels transactions rather than delaying cleanup.

I think it's the opposite, isn't it? vacuum_defer_cleanup_age
prevents cancellations.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company