Re: reloption to prevent VACUUM from truncating empty pages at the end of relation

On Wed, Apr 18, 2018 at 7:46 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> On 2018-04-18 10:46:51 +0900, Michael Paquier wrote:
>> On Tue, Apr 17, 2018 at 06:13:31PM -0700, Andres Freund wrote:
>> > Not sure what you mean?
>>
>> Do you need help on it? I suggest that I could undertake the proposed
>> patch and submit it earlier in the development cycle of v12.
>
> I think it's at the very least two months of serious development work to
> get it into a state ready for submission. And a good chunk of that not
> even sketched out. Replacing the hashtable is the easy part, the memory
> management (Complicated due to lock-freeness. I'm thinking of using a
> variant of epoch based reclamation) isn't really there, the management
> of shared "open relations" state are the hard parts...
>
> So yes, I could use help on it, but it'll be a lot of actual design and
> investigatory work.
>

I think it makes sense to pursue that approach, but it might be worth
considering some alternative till we have it. I remember last time
(in 2015) we have discussed some another solution [1] to this problem
(or similar) and we have left it unattended in the hope that we will
get a better solution, but we are still in the same situation. I
think in general it is better to go with the approach which can fix
the root cause of the problem, but if that is going to take a long
time, it is not terrible to provide some workable solution which can
help users.

[1] - https://www.postgresql.org/message-id/CAA4eK1JPLGjpMeJ5YLNE7bpNBhP2EQe_rDR%2BAw3atNfj9WkAGg%40mail.gmail.com

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com