Re: [Postgres-xc-developers] Patch ready for review: online data redistribution

Because this is a bulk operation, applications may need full access to the table, I mean, read and write during the redistribution.    May be providec by lower level of locking.    People would like to see latest view of the table so running whole ALTER TABLE as a single transaction may not be satisfactory.

Regards;
---
Koichi Suzuki

On Tue, 17 Jul 2012 13:08:46 +0900
Michael Paquier <mic...@gm...> wrote:

> On Tue, Jul 17, 2012 at 1:06 PM, Koichi Suzuki <koi...@gm...>wrote:
> 
> > People don't like to stop application operation.   It is very painful.
> >   Current ALTER TABLE blocks application so we have to stop involved
> > applications for a while.   CONCURRENT operation don't require this,
> > although it may take longer.
> >
> By blocking application, I think it means that an exclusive lock is taken
> on the table being altered, so other sessions cannot access to it.
> In this case CONCURRENT means that we do an ALTER TABLE by taking a lower
> locking level and authorize other sessions to read and/or modify data
> altered.
> -- 
> Michael Paquier
> http://michael.otacoo.com