Re: The quickest way to migrate database within the same cluster

I'm using 9.1
Will foreign data wrapper have similar performance issue as dblink?

Thanks,
Wendy

-----Original Message-----
From: Ian Barwick [mailto:ian(at)2ndquadrant(dot)com]
Sent: Sunday, January 04, 2015 3:13 PM
To: Zheng, Wendy; pgsql-admin(at)postgresql(dot)org
Subject: Re: [ADMIN] The quickest way to migrate database within the same cluster

On 15/01/04 15:52, Zheng, Wendy wrote:
> Hi PgSql experts,
>
> I'm working on a task to move tables from on database to another
> within the same cluster and same server. I try the pg_dump and
> pg_restore commands (with -Fc option), and notice that it costs around
> half an hour which is not acceptable. Then I try to move the data
> files directly. I create the same tables in the new DB, find out the
> directory stores the data file and search for the data files by the
> table name, then move the corresponding data file in the old DB to the
> new one. This is very quick, and looks like the DB still works. But I
> have a concern that whether there will any other problem if I doing this?

Yes, you'll experience massive data corruption. You can't just manually copy data files around, even though it might seem to work.

> Another workaround is to access the old DB in the new DB with dblink
> (I created a view with dblink and use it as if the view as if the
> table is in the new DB). But we soon notice that even though we
> specify the criteria in the select command, dblink will still retrieve
> all the records first, and then apply the search criteria. This brings
> poor performance. Do you have any better idea how can I handle this?

Which PostgreSQL version are you using? If 9.3 or later you can use a foreign data wrapper (postgres_fdw) to access data in another database (including on the same cluster).

Regards

Ian Barwick

--
Ian Barwick http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, RemoteDBA, Training & Services