Re: "DB Link are Inherently Slow" -- True or False?

On Tue, Jul 15, 2008 at 6:23 AM, David Aldridge <david_at_david-aldridge.com> wrote:

> I am being persistently told by a DBA that DB links are inherently slow
> and not suited to bulk transfer of data.
>
> Does anyone have any experiences to share on the sort of practical
> MBytes/sec throughput we ought to be getting on a 10GBit network between two
> databases having no intervening firewalls, routers, or other potentially
> performance limiting network components? We're seeing 2MBytes/sec using data
> pump import in network mode with parallelsim of 10 (ie. sourcing data
> through a db link from another db on a different host) :(
>

Hi David,

The referred to slowness is probably due to the sometimes sub-optimal execution
plans that are generated when some of the data is obtained via dblink in multi-table queries.

You may want to google for this, it is an issue that has appeared in the past,
and there are some workarounds - hints (driving_site is one) and use of views
and some other hints.

The problem was often that a FTS was done on the remote table(s) when that would not have been the case if the table were local.

You may want to check on any improvements for this in 10g/11g, I haven't looked
at it myself in quite awhile.

-- 
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist

--
http://www.freelists.org/webpage/oracle-l