Re: [Proposal] Global temporary tables

> 2020年1月6日 下午8:17，Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> 写道：
>
> On Mon, 6 Jan 2020 at 11:01, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>>
>> On Mon, Jan 06, 2020 at 01:04:15PM +0800, 曾文旌(义从) wrote:
>>
>>> 2 We feel that gtt needs to maintain statistics, but there is no
>>> agreement on what it will be done.
>>>
>>
>> I certainly agree GTT needs to maintain statistics, otherwise it'll lead
>> to poor query plans.
>
> +1
>
>> AFAIK the current patch stores the info in a hash
>> table in a backend private memory, and I don't see how else to do that
>> (e.g. storing it in a catalog would cause catalog bloat).
>>
>
> It sounds like it needs a pair of system GTTs to hold the table and
> column statistics for other GTTs. One would probably have the same
> columns as pg_statistic, and the other just the relevant columns from
> pg_class. I can see it being useful for the user to be able to see
> these stats, so perhaps they could be UNIONed into the existing stats
> view.
The current patch provides several functions as extension(pg_gtt) for read gtt statistics.
Next I can move them to the kernel and let the view pg_stats can see gtt’s statistics.

> Regards,
> Dean