Date: Sun, 12 Jan 2020 02:14:01 +0100
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
Cc: =?utf-8?B?5pu+5paH5peMKOS5ieS7jik=?= <wenjing.zwj@alibaba-inc.com>,
	Pavel Stehule <pavel.stehule@gmail.com>,
	Robert Haas <robertmhaas@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@postgresql.org>,
	=?utf-8?B?6JSh5p2+6ZyyKOWtkOWYiSk=?= <zijia@taobao.com>,
	"Cai, Le" <le.cai@alibaba-inc.com>,
	=?utf-8?B?6JCn5bCR6IGqKOmTgeW6tSk=?= <shaocong.xsc@alibaba-inc.com>
Subject: Re: [Proposal] Global temporary tables
Message-ID: <20200112011401.zwvvxoywrrivl542@development>
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On Fri, Jan 10, 2020 at 03:24:34PM +0300, Konstantin Knizhnik wrote:
>
>
>On 09.01.2020 19:30, Tomas Vondra wrote:
>
>
>>
>>>
>>>>
>>>>>3 Still no one commented on GTT's transaction information 
>>>>>processing, they include
>>>>>3.1 Should gtt's frozenxid need to be care?
>>>>>3.2 gtt’s clog clean
>>>>>3.3 How to deal with "too old" gtt data
>>>>>
>>>>
>>>>No idea what to do about this.
>>>>
>>>
>>>I wonder what is the specific of GTT here?
>>>The same problem takes place for normal (local) temp tables, doesn't it?
>>>
>>
>>Not sure. TBH I'm not sure I understand what the issue actually is.
>
>Just open session, create temporary table and insert some data in it.
>Then in other session run 2^31 transactions (at my desktop it takes 
>about 2 hours).
>As far as temp tables are not proceeded by vacuum, database is stalled:
>
> ERROR:  database is not accepting commands to avoid wraparound data 
>loss in database "postgres"
>
>It seems to be quite dubious behavior and it is strange to me that 
>nobody complains about it.
>We discuss  many issues related with temp tables (statistic, parallel 
>queries,...) which seems to be less critical.
>
>But this problem is not specific to GTT - it can be reproduced with 
>normal (local) temp tables.
>This is why I wonder why do we need to solve it in GTT patch.
>

Yeah, I think that's out of scope for GTT patch. Once we solve it for
plain temporary tables, we'll solve it for GTT too.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services