Xapian discuss - Nov 2009 - [Xapian discuss] Is there difference between single database and multiple database?

Hi, all:

      I am not quite clear about the internal process of query in xapian, is
there any differences between querying in a single database and a multiple
database, if both of them have the same amount of data?

    For example, the single database has n documents,   which is equal to
the total documents' count of the databases in the multiple database ?

    What are the differences between querying in them ? Is there any
performance difference ?

-- 
Best wishes from Ray ...

On Sat, Nov 14, 2009 at 10:13:26PM +0800, ?????????
wrote:
>       I am not quite clear about the internal process of query in xapian,
is
> there any differences between querying in a single database and a multiple
> database, if both of them have the same amount of data?
>
>     For example, the single database has n documents,   which is equal to
> the total documents' count of the databases in the multiple database ?
No, they should behave identically.

The only difference is with get_eset() where term frequencies are
approximated based on the first database listed is used unless
Xapian::Enquire::USE_EXACT_TERMFREQ is specified.
>     What are the differences between querying in them ? Is there any
> performance difference ?
I don't think anyone has done much any very extensive comparisons of this.
My very limited tests suggest there's not much overhead, but if you're
interested to know it isn't too hard to set up such tests (please report
back if you do!)

Cheers,
    Olly