Re: Problems with postgres online backup - restore

Hello,

I'd like to understand the PostgreSQL internals in "backup mode".

When I understood it correctly pg_start_backup() make a checkpoint and
stops writing to the data/ directory except the WAL.

All new transaction go into WAL which is also logical. But how is data
consistency done when the written/changed blocks don't fit into the buffer
cache?

E.g.
A lot of updates which exceed buffer cache (Where is data written except
WAL since data should be kept constant?)
SELECT FROM updated data: WHERE is the new data fetched from?

Thnx for any explainations.

Ciao,
Gerhard

--
http://www.wiesinger.com/

On Thu, 25 Jun 2009, Chris Barnes wrote:

>
> SELECT pg_switch_xlog();
>
> SELECT pg_start_backup('postres_full_backup_June222009');
>
> tar -czvf pgprd01_June22_2009_production.dmp.tar.gz data/
>
> SELECT pg_stop_backup();
>