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

2020年2月2日 上午2:00，Pavel Stehule <pavel.stehule@gmail.com> 写道：

so 1. 2. 2020 v 14:39 odesílatel 曾文旌(义从) <wenjing.zwj@alibaba-inc.com> napsal:

2020年1月30日 下午10:21，Pavel Stehule <pavel.stehule@gmail.com> 写道：

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 tried to optimize code in global_temporary_table_v10-pg13.patch

Please give me feedback.

I tested this patch and I have not any objections - from my user perspective it is work as I expect

+#define RELATION_IS_TEMP(relation) \
+ ((relation)->rd_islocaltemp || \
+ (relation)->rd_rel->relpersistence == RELPERSISTENCE_GLOBAL_TEMP)
 

It looks little bit unbalanced

maybe is better to inject rd_isglobaltemp to relation structure

and then

it should to like

+#define RELATION_IS_TEMP(relation) \
+ ((relation)->rd_islocaltemp || \
+ (relation)->rd_isglobaltemp))

But I have not idea if it helps in complex

In my opinion

For local temp table we need (relation)->rd_rel->relpersistence == RELPERSISTENCE_TEMP 

and because one local temp table belongs to only one session, need to mark one sessions rd_islocaltemp = true ,and other to rd_islocaltemp = false.

But For GTT, just need (relation)->rd_rel->relpersistence == RELPERSISTENCE_GLOBAL_GLOBAL_TEMP

One GTT can be used for every session, so no need rd_isglobaltemp anymore. This seems duplicated and redundant.

Wenjing

Wenjing




>
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> Robert Haas
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