On 25/11/2007, Erik Jones <erik@myemma.com> wrote: On Nov 25, 2007, at 10:46 AM, Pablo Alcaraz wrote:
> Hi all,
>
> I read that pg_dump can run while the database is being used and makes
> "consistent backups".
>
> I have a huge and *heavy* selected, inserted and updated database.
> Currently I have a cron task that disconnect the database users,
> make a
> backup using pg_dump and put the database online again. The problem
> is,
> now there are too much information and everyday the database store
> more
> and more data, the backup process needs more and more time to run
> and I
> am thinking about to do the backup using a process that let me to
> do it
> with the minimal interruptions for the users.
>
> I do not need a last second backup. I could the a backup with "almost
> all" the data but I need the information on it to be coherent. For
> example, if the backup store information about an invoice it *must* to
> store both header and items invoice information. I could live if the
> backup does not store some invoices information when is ran, because
> they ll be backuped the next time the backup process run. But I can
> not
> store only a part of the invoices. That is I call a coherent backup.
>
> The best for me is that the cron tab does a concurrent backup with all
> the information until the time it starts to run while the clients are
> using the database. Example: if the cron launch the backup process at
> 12:30 AM, the backup moust be builded with all the information *until*
> 12:30AM. So if I need to restore it I get a database coherent with the
> same information like it was at 12:30AM. it does not matter if the
> process needs 4 hours to run.
>
> Does the pg_dump create this kind of "consistent backups"? Or do I
> need
> to do the backups using another program?
Yes, that is exactly what pg_dump does.
Yes so long as you are using transactions correctly. Ie doing a begin before each invoice and a commit afterwards if your not bothering and using auto commit you *may* have problems. pg_dump will show a constant state at the time when the backup was started. If your database was not "consistent" at that time you may have issues, But it will be constant from a database point of view ie foreign keys, primary keys, check constraints, triggers etc.
It all depends what you mean by consistent.
Peter.
