| From: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
|---|---|
| To: | Julien Rouhaud <rjuju123(at)gmail(dot)com> |
| Cc: | Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru>, 曾文旌(义从) <wenjing(dot)zwj(at)alibaba-inc(dot)com>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, 蔡松露(子嘉) <zijia(at)taobao(dot)com>, "Cai, Le" <le(dot)cai(at)alibaba-inc(dot)com>, 萧少聪(铁庵) <shaocong(dot)xsc(at)alibaba-inc(dot)com> |
| Subject: | Re: [Proposal] Global temporary tables |
| Date: | 2020-01-13 21:03:01 |
| Message-ID: | 20200113210301.yakqxdmxjh2ogq6x@development |
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| Lists: | pgsql-hackers |
On Mon, Jan 13, 2020 at 09:12:38PM +0100, Julien Rouhaud wrote:
>On Mon, Jan 13, 2020 at 05:32:53PM +0100, Tomas Vondra wrote:
>> On Mon, Jan 13, 2020 at 11:08:40AM +0300, Konstantin Knizhnik wrote:
>> >
>> >"if any code tried to access the statistics directly from the table,
>> >rather than via the caches".
>> >
>> >Currently optimizer is accessing statistic though caches. So this
>> >approach works. If somebody will rewrite optimizer or provide own
>> >custom optimizer in extension which access statistic directly
>> >then it we really be a problem. But I wonder why bypassing catalog
>> >cache may be needed.
>> >
>>
>> I don't know, but it seems extensions like hypopg do it.
>
>AFAIR, hypopg only opens pg_statistic to use its tupledesc when creating
>statistics on hypothetical partitions, but it should otherwise never reads or
>need plain pg_statistic rows.
Ah, OK! Thanks for the clarification. I knew it does something with the
catalog, didn't realize it only gets the descriptor.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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