Re: Temporary tables prevent autovacuum, leading to XID wraparound

On Thu, Feb 1, 2018 at 2:01 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Tue, Jan 30, 2018 at 7:04 PM, Tsunakawa, Takayuki
> <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> wrote:
>> So a simple improvement would be to assign workers fairly to databases facing a wraparound risk, as Sawada-san suggested.
>
> Is that always an improvement, or does it make some cases better and
> others worse?

I think the idea would not be an improvement, but just change the
policy. The current launcher's policy is "let's launch a new worker as
much as possible on the database that is at risk of wraparound most".
The idea I suggested makes the cases mentioned on this thread better
while perhaps making other cases worse.

To improve while keeping the current policy, we might want to use the
first idea I proposed. That is, we don't launch a new worker on a
database impending wraparound if the last table of the database is
being vacuumed. But it needs to share new information such as what
tables exist in each database and which tables already have worker. It
might be overkill in order to deal with only such a corner case
though.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center