Re: Allowing multiple concurrent base backups

On 11.01.2011 20:51, Tom Lane wrote:
> Heikki Linnakangas<heikki.linnakangas@enterprisedb.com>  writes:
>> I implemented this in two ways, and can't decide which I like better:
>
>> 1. The contents of the backup label file are returned to the caller of
>> do_pg_start_backup() as a palloc'd string.
>
>> 2. do_pg_start_backup() creates a temporary file that the backup label
>> is written to (instead of "backup_label").
>
>> Implementation 1 changes more code, as pg_start/stop_backup() need to be
>> changed to write/read from memory instead of file, but the result isn't
>> any more complicated. Nevertheless, I somehow feel more comfortable with 2.
>
> Seems like either one of these is fairly problematic in that you have to
> have some monstrous kluge to get the backup_label file to appear with
> the right name in the tarfile.

Oh. I'm surprised you feel that way - that part didn't feel ugly or 
kludgey at all to me.

>  How badly do we actually need this?
> I don't think the use-case for concurrent base backups is all that large
> in practice given the I/O hit it's going to involve.

It makes it very convenient to set up standbys, without having to worry 
that you'll conflict e.g with a nightly backup. I don't imagine people 
will use streaming base backups for very large databases anyway.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com