Re: [Proposal] Global temporary tables

2020年2月15日 下午6:06，Pavel Stehule <pavel.stehule@gmail.com> 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




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