Re: Temporary tables prevent autovacuum, leading to XID wraparound

On Wed, Feb 07, 2018 at 12:37:50AM +0000, Tsunakawa, Takayuki wrote:
> From: Michael Paquier [mailto:michael(dot)paquier(at)gmail(dot)com]
>> I am not sure that we would like to give up that easily the property that
>> we have now to clean up past temporary files only at postmaster startup
>> and only when not in recovery. If you implement that, there is a risk that
>> the backend you are starting is eating the connection slot and by consequence
>> its temporary schema and its set of temporary tables on which one may want
>> to look into after a crash.
>
> postmaster deletes temporary relation files at startup by calling
> RemovePgTempFiles() regardless of whether it's in recovery. It
> doesn't call that function during auto restart after a crash when
> restart_after_crash is on.

The comment on top of RemovePgTempFiles() states the following:
* NOTE: we could, but don't, call this during a post-backend-crash restart
* cycle. The argument for not doing it is that someone might want to examine
* the temp files for debugging purposes. This does however mean that
* OpenTemporaryFile had better allow for collision with an existing temp
* file name.

>> > 2. Teach autovacuum to remove any leftover tables in a pg_temp_%d
>> > schema if the backend is active but in some other database (rather
>> > than only when the backend is not active at all).
>>
>> Yeah. Here we can do something. This does not sound much difficult to
>> me.
>
> I did that in my patch.

Nice to hear that. Please note that I did not check your patch, so I
cannot conclude on its correctness in details.
--
Michael