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

2020年8月7日 下午5:30，movead.li@highgo.ca 写道：

>I find this is the most latest mail with an attachment, so I test and reply on

>this thread, several points as below:

>1. I notice it produces new relfilenode when new session login and some

>data insert. But the relfilenode column in pg_class still the one when create

>the global temp table. I think you can try to show 0 in this area as what nail

>relation does. 

>I think getting the GTT to have a default relfilenode looks closer to the existing implementation, and setting it to 0 requires extra work and has no clear benefit.

>What do you think？

>I'd like to know the reasons for your suggestion.

The 'relfilenode' mean the file no on disk which different from oid of a relation,

 the default one is a wrong for gtt, so I think it's not so good to show it in 

pg_class.

>2. The nail relations handle their relfilenodes by RelMapFile struct, and this

>patch use hash entry and relfilenode_list, maybe RelMapFile approach more

>understandable in my opinion. Sorry if I miss the real design for that.

>We can see the STORAGE and statistics info for the GTT, including relfilenode, through view pg_gtt_relstats

postgres=# \d gtt

                Table "public.gtt"

 Column |  Type   | Collation | Nullable | Default 

--------+---------+-----------+----------+---------

 a      | integer |           |          | 

 b      | integer |           |          | 

postgres=# insert into gtt values(1,1);

INSERT 0 1

postgres=# select * from pg_gtt_relstats ;

 schemaname | tablename | relfilenode | relpages | reltuples | relallvisible | relfrozenxid | relminmxid 

------------+-----------+-------------+----------+-----------+---------------+--------------+------------

 public     | gtt       |       16384 |        0 |         0 |             0 |          532 |          1

(1 row)

postgres=# truncate gtt;

TRUNCATE TABLE

postgres=# select * from pg_gtt_relstats ;

 schemaname | tablename | relfilenode | relpages | reltuples | relallvisible | relfrozenxid | relminmxid 

------------+-----------+-------------+----------+-----------+---------------+--------------+------------

 public     | gtt       |       16387 |        0 |         0 |             0 |          533 |          1

(1 row)

I just suggest a way which maybe most naturely to the exist code struct, and it's

uo to you.

>3. I get a wrong result of pg_relation_filepath() function for global temp table,

>I think it's necessaryto keep this an correct output.

postgres=# select pg_relation_filepath(oid) from pg_class where relname = 'gtt';

 pg_relation_filepath 

----------------------

 base/13835/t3_16384

(1 row)

I didn't find anything wrong. Could you please give me a demo.

In my opinoin it should show 'base/13835/t3_16387', other than 'base/13835/t3_16384',

because the relfilenode change to 16387 when you truncate it in step 2.

>4. In gtt_search_by_relid() function, it has not handle the missing_ok argument

>if gtt_storage_local_hash is null. There should be some comments if it's the right

>code.

>This is a problem that has been fixed in global_temporary_table_v34-pg13.patch.

Sorry about it, I can not find it in mail thread and maybe I miss something. The mail thread

is so long, it's better to create a new mail thread I think.

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Regards,

Highgo Software (Canada/China/Pakistan)
URL : www.highgo.ca
EMAIL: mailto:movead(dot)li(at)highgo(dot)ca