Re: [Proposal] Global temporary tables - Mailing list pgsql-hackers

2020年2月14日 下午5:19，Pavel Stehule <pavel.stehule@gmail.com> 写道：

čt 30. 1. 2020 v 15:21 odesílatel Pavel Stehule <pavel.stehule@gmail.com> napsal:

čt 30. 1. 2020 v 15:17 odesílatel 曾文旌(义从) <wenjing.zwj@alibaba-inc.com> napsal:

> 2020年1月29日 下午9:48，Robert Haas <robertmhaas@gmail.com> 写道：
>
> On Tue, Jan 28, 2020 at 12:12 PM 曾文旌(义从) <wenjing.zwj@alibaba-inc.com> wrote:
>>> Opinion by Pavel
>>> + rel->rd_islocaltemp = true;  <<<<<<< if this is valid, then the name of field "rd_islocaltemp" is not probably best
>>> I renamed rd_islocaltemp
>>
>> I don't see any change?
>>
>> Rename rd_islocaltemp to rd_istemp  in global_temporary_table_v8-pg13.patch
>
> In view of commit 6919b7e3294702adc39effd16634b2715d04f012, I think
> that this has approximately a 0% chance of being acceptable. If you're
> setting a field in a way that is inconsistent with the current use of
> the field, you're probably doing it wrong, because the field has an
> existing purpose to which new code must conform. And if you're not
> doing that, then you don't need to rename it.
Thank you for pointing it out.
I've rolled back the rename.
But I still need rd_localtemp to be true, The reason is that
1 GTT The GTT needs to support DML in read-only transactions ,like local temp table.
2 GTT does not need to hold the lock before modifying the index buffer ,also like local temp table.

Please give me feedback.

maybe some like

rel->rd_globaltemp = true;

and somewhere else

if (rel->rd_localtemp || rel->rd_globaltemp)

{

  ...

}

I tested this patch again and I am very well satisfied with behave.

what doesn't work still - TRUNCATE statement

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.

Regards

Pavel

Wenjing




>
> --
> Robert Haas
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