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Re: Declarative partitioning

From: David Fetter <david(at)fetter(dot)org>
To: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
Cc: Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Declarative partitioning
Date: 2015-08-18 13:43:23
Message-ID: 20150818134323.GC18054@fetter.org (view raw, whole thread or download thread mbox)
Thread:
Lists: pgsql-hackers
On Tue, Aug 18, 2015 at 07:30:20PM +0900, Amit Langote wrote:
> Hi,
> 
> I would like propose $SUBJECT for this development cycle. Attached is a
> WIP patch that implements most if not all of what's described below. Some
> yet unaddressed parts are mentioned below, too. I'll add this to the CF-SEP.

Thanks for pushing this forward!  We've needed this done for at least
a decade.

> 4. (yet unimplemented) Attach partition (from existing table)
> 
> ALTER TABLE partitioned_table
> ATTACH PARTITION partition_name
> FOR VALUES values_spec
> USING [TABLE] table_name;
> 
> ALTER TABLE table_name
> SET VALID PARTITION OF <parent>;
> 
> The first of the above pair of commands would attach table_name as a (yet)
> 'invalid' partition of partitioned_table (after confirming that it matches
> the schema and does not overlap with other partitions per FOR VALUES
> spec). It would also record the FOR VALUES part in the partition catalog
> and set pg_class.relispartition to true for table_name.
> 
> After the first command is done, the second command would take exclusive
> lock on table_name, scan the table to check if it contains any values
> outside the boundaries defined by FOR VALUES clause defined previously,
> throw error if so, mark as valid partition of parent if not.

One small change to make this part more efficient:

1. Take the access exclusive lock on table_name.
2. Check for a matching constraint on it.
3. If it's there, mark it as a valid partition.
4. If not, check for values outside the boundaries as above.

Should the be a *valid* constraint?  Perhaps that should be
parameterized, as I'm not yet seeing a compelling argument either
direction.  I'm picturing something like:

    ALTER TABLE table_name SET VALID PARTITION OF <parent> [TRUST]

where TRUST would mean that an existing constraint need not be VALID.

> Does that make sense?

Yep.

> 5. Detach partition
> 
> ALTER TABLE partitioned_table
> DETACH PARTITION partition_name [USING table_name]
> 
> This removes partition_name as partition of partitioned_table. The table
> continues to exist with the same name or 'table_name', if specified.
> pg_class.relispartition is set to false for the table, so it behaves like
> a normal table.

Could this take anything short of an access exclusive lock on the
parent?

Cheers,
David.
-- 
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778  AIM: dfetter666  Yahoo!: dfetter
Skype: davidfetter      XMPP: david(dot)fetter(at)gmail(dot)com

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