Fwd: Re: handle tablespaces for partitioned tables during ALTERDATABASE

(Forgot to CC pgsql-bugs.)

Jason

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Date: Tue, 24 Mar 2020 14:24:33 -0700
From: postgres@jasonk.me
To: Andres Freund <andres@anarazel.de>
Subject: Re: handle tablespaces for partitioned tables during ALTER DATABASE
Message-ID: <20200324212433.3knuzvcpc3idjm2b@jasonk.me>
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    <20200324192359.yw7q5rlfqqxoktl6@alap3.anarazel.de>
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In-Reply-To: <20200324192359.yw7q5rlfqqxoktl6@alap3.anarazel.de>

Hi, Andres.

On 2020-03-24T12:23:59-0700, Andres Freund wrote:
> I don't immediately see what problem this could cause? There's no
> physical file associated with a partitioned table, it's "just" a
> template for new partitions of that partitioned table.

I had illustrated a plausible scenario where this could be _unexpected_.  The
state that you can get into after the first `ALTER DATABASE` is strange because
the tablespace of `scores_rank_0_to_100` is not `InvalidOid` yet equal to the
database's tablespace.

You can't get into this state normally: try

```sql
CREATE DATABASE f TABLESPACE fast;
\c f
CREATE TABLE t (i int, j int) PARTITION BY RANGE (i);
CREATE TABLE t0 PARTITION OF t FOR VALUES FROM (0) TO (100) TABLESPACE fast;
SELECT relname, reltablespace FROM pg_class WHERE relname LIKE 't0';
```

```
 relname | reltablespace 
---------+---------------
 t0      |             0
(1 row)
```

Notice that it's `InvalidOid`, not the explicit database's tablespace.  But you
can get into that state with some work, like I illustrated in my example in the
first message.

For less confusion, I think it makes sense to prohibit this or seamlessly
convert the appropriate `reltablespace` values to `InvalidOid`.  Enforcing this
may also give me less things to worry about for my own work.

Jason

----- End forwarded message -----