Re: [Proposal] Global temporary tables

> 2020年1月22日 下午2:31，Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> 写道：
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> st 22. 1. 2020 v 7:16 odesílatel 曾文旌(义从) <wenjing(dot)zwj(at)alibaba-inc(dot)com <mailto:wenjing(dot)zwj(at)alibaba-inc(dot)com>> napsal:
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>> 2020年1月22日 上午2:51，Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com <mailto:pavel(dot)stehule(at)gmail(dot)com>> 写道：
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>> út 21. 1. 2020 v 9:46 odesílatel 曾文旌(义从) <wenjing(dot)zwj(at)alibaba-inc(dot)com <mailto:wenjing(dot)zwj(at)alibaba-inc(dot)com>> napsal:
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>>> 2020年1月12日 上午4:27，Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com <mailto:pavel(dot)stehule(at)gmail(dot)com>> 写道：
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>>> Hi
>>>
>>> so 11. 1. 2020 v 15:00 odesílatel 曾文旌(义从) <wenjing(dot)zwj(at)alibaba-inc(dot)com <mailto:wenjing(dot)zwj(at)alibaba-inc(dot)com>> napsal:
>>> Hi all
>>>
>>> This is the latest patch
>>>
>>> The updates are as follows:
>>> 1. Support global temp Inherit table global temp partition table
>>> 2. Support serial column in GTT
>>> 3. Provide views pg_gtt_relstats pg_gtt_stats for GTT’s statistics
>>> 4. Provide view pg_gtt_attached_pids to manage GTT
>>> 5. Provide function pg_list_gtt_relfrozenxids() to manage GTT
>>> 6. Alter GTT or rename GTT is allowed under some conditions
>>>
>>>
>>> Please give me feedback.
>>>
>>> I tested the functionality
>>>
>>> 1. i think so "ON COMMIT PRESERVE ROWS" should be default mode (like local temp tables).
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>> ON COMMIT PRESERVE ROWS is default mode now.
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>> Thank you
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>> * I tried to create global temp table with index. When I tried to drop this table (and this table was used by second instance), then I got error message
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>> postgres=# drop table foo;
>> ERROR: can not drop index when other backend attached this global temp table
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>> It is expected, but it is not too much user friendly. Is better to check if you can drop table, then lock it, and then drop all objects.
> I don't understand what needs to be improved. Could you describe it in detail?
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> the error messages should be some like
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> can not drop table when other backend attached this global temp table.
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> It is little bit messy, when you try to drop table and you got message about index
It has been repaired in global_temporary_table_v7-pg13.patch

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>> * tab complete can be nice for CREATE GLOBAL TEMP table
> Yes, I will improve it.
It has been repaired in global_temporary_table_v7-pg13.patch

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>> \dt+ \di+ doesn't work correctly, or maybe I don't understand to the implementation.
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> postgres=# create table t(a int primary key);
> CREATE TABLE
> postgres=# create global temp table gt(a int primary key);
> CREATE TABLE
> postgres=# insert into t values(generate_series(1,10000));
> INSERT 0 10000
> postgres=# insert into gt values(generate_series(1,10000));
> INSERT 0 10000
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> postgres=# \dt+
> List of relations
> Schema | Name | Type | Owner | Persistence | Size | Description
> --------+------+-------+-------------+-------------+--------+-------------
> public | gt | table | wenjing.zwj | session | 384 kB |
> public | t | table | wenjing.zwj | permanent | 384 kB |
> (2 rows)
>
> postgres=# \di+
> List of relations
> Schema | Name | Type | Owner | Table | Persistence | Size | Description
> --------+---------+-------+-------------+-------+-------------+--------+-------------
> public | gt_pkey | index | wenjing.zwj | gt | session | 240 kB |
> public | t_pkey | index | wenjing.zwj | t | permanent | 240 kB |
> (2 rows)
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>> I see same size in all sessions. Global temp tables shares same files?
> No, they use their own files.
> But \dt+ \di+ counts the total file sizes in all sessions for each GTT.
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> I think so it is wrong. The data are independent and the sizes should be independent too
It has been repaired in global_temporary_table_v7-pg13.patch.

Wenjing

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> Wenjing
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>> Regards
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>> Pavel
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>> Wenjing
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>>>
>>> I tested some simple scripts
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>>> test01.sql
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>>> CREATE TEMP TABLE foo(a int, b int);
>>> INSERT INTO foo SELECT random()*100, random()*1000 FROM generate_series(1,1000);
>>> ANALYZE foo;
>>> SELECT sum(a), sum(b) FROM foo;
>>> DROP TABLE foo; -- simulate disconnect
>>>
>>>
>>> after 100 sec, the table pg_attribute has 3.2MB
>>> and 64 tps, 6446 transaction
>>>
>>> test02.sql
>>>
>>> INSERT INTO foo SELECT random()*100, random()*1000 FROM generate_series(1,1000);
>>> ANALYZE foo;
>>> SELECT sum(a), sum(b) FROM foo;
>>> DELETE FROM foo; -- simulate disconnect
>>>
>>>
>>> after 100 sec, 1688 tps, 168830 transactions
>>>
>>> So performance is absolutely different as we expected.
>>>
>>> From my perspective, this functionality is great.
>>>
>>> Todo:
>>>
>>> pg_table_size function doesn't work
>>>
>>> Regards
>>>
>>> Pavel
>>>
>>>
>>> Wenjing
>>>
>>>
>>>
>>>
>>>
>>>> 2020年1月6日 上午4:06，Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com <mailto:tomas(dot)vondra(at)2ndquadrant(dot)com>> 写道：
>>>>
>>>> Hi,
>>>>
>>>> I think we need to do something with having two patches aiming to add
>>>> global temporary tables:
>>>>
>>>> [1] https://commitfest.postgresql.org/26/2349/ <https://commitfest.postgresql.org/26/2349/>
>>>>
>>>> [2] https://commitfest.postgresql.org/26/2233/ <https://commitfest.postgresql.org/26/2233/>
>>>>
>>>> As a reviewer I have no idea which of the threads to look at - certainly
>>>> not without reading both threads, which I doubt anyone will really do.
>>>> The reviews and discussions are somewhat intermixed between those two
>>>> threads, which makes it even more confusing.
>>>>
>>>> I think we should agree on a minimal patch combining the necessary/good
>>>> bits from the various patches, and terminate one of the threads (i.e.
>>>> mark it as rejected or RWF). And we need to do that now, otherwise
>>>> there's about 0% chance of getting this into v13.
>>>>
>>>> In general, I agree with the sentiment Rober expressed in [1] - the
>>>> patch needs to be as small as possible, not adding "nice to have"
>>>> features (like support for parallel queries - I very much doubt just
>>>> using shared instead of local buffers is enough to make it work.)
>>>>
>>>> regards
>>>>
>>>> --
>>>> Tomas Vondra http://www.2ndQuadrant.com <http://www.2ndquadrant.com/>
>>>> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>>>
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