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From: =?UTF-8?B?5pu+5paH5peMKOS5ieS7jik=?= <[email protected]>
To: Pavel Stehule <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: Tomas Vondra <[email protected]>
Cc: Konstantin Knizhnik <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: =?UTF-8?B?6JSh5p2+6ZyyKOWtkOWYiSk=?= <[email protected]>
Cc: =?UTF-8?B?Q2FpLCBMZQ==?= <[email protected]>
Cc: =?UTF-8?B?6JCn5bCR6IGqKOmTgeW6tSk=?= <[email protected]>
Subject: Re: [Proposal] Global temporary tables
Date: Sun, 16 Feb 2020 23:16:19 +0800
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAFj8pRCz52CbxnNmO=NK7cBA=9o=rdWVEBJRKOeVJ1FwzqzLRw@mail.gmail.com>
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> 2020年2月15日 下午6:06，Pavel Stehule <[email protected]> 写道：
> 
> 
>> postgres=# insert into foo select generate_series(1,10000);
>> INSERT 0 10000
>> postgres=# \dt+ foo
>>                           List of relations
>> ┌────────┬──────┬───────┬───────┬─────────────┬────────┬─────────────┐
>> │ Schema │ Name │ Type  │ Owner │ Persistence │  Size  │ Description │
>> ╞════════╪══════╪═══════╪═══════╪═════════════╪════════╪═════════════╡
>> │ public │ foo  │ table │ pavel │ session     │ 384 kB │             │
>> └────────┴──────┴───────┴───────┴─────────────┴────────┴─────────────┘
>> (1 row)
>> 
>> postgres=# truncate foo;
>> TRUNCATE TABLE
>> postgres=# \dt+ foo
>>                           List of relations
>> ┌────────┬──────┬───────┬───────┬─────────────┬───────┬─────────────┐
>> │ Schema │ Name │ Type  │ Owner │ Persistence │ Size  │ Description │
>> ╞════════╪══════╪═══════╪═══════╪═════════════╪═══════╪═════════════╡
>> │ public │ foo  │ table │ pavel │ session     │ 16 kB │             │
>> └────────┴──────┴───────┴───────┴─────────────┴───────┴─────────────┘
>> (1 row)
>> 
>> I expect zero size after truncate.
> Thanks for review.
> 
> I can explain, I don't think it's a bug.
> The current implementation of the truncated GTT retains two blocks of FSM pages.
> The same is true for truncating regular tables in subtransactions.
> This is an implementation that truncates the table without changing the relfilenode of the table.
> 
> 
> This is not extra important feature - now this is little bit a surprise, because I was not under transaction.
> 
> Changing relfilenode, I think, is necessary, minimally for future VACUUM FULL support.
Not allowing relfilenode changes is the current limit.
I think can improve on it. But ,This is a bit complicated.
so I'd like to know the necessity of this improvement.
Could you give me more details?

> 
> Regards
> 
> Pavel Stehule
>  
> 
> Wenjing
> 
>> 
>> Regards
>> 
>> Pavel
>> 
>> 
>> 
>> Wenjing
>> 
>> 
>> 
>> 
>> > 
>> > -- 
>> > Robert Haas
>> > EnterpriseDB: http://www.enterprisedb.com <http://www.enterprisedb.com/;
>> > The Enterprise PostgreSQL Company
>> 
> 

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