[Xapian-devel] Lucene 3.6.2 backend for xapian (#25)

[jiangwen jiang]

OK， I will try to adjust the code to xapian multi-database, it will spend
some time

Thanks!


2013/10/31 Olly Betts <olly at survex.com>

> On Thu, Oct 31, 2013 at 10:24:26AM +0800, jiangwen jiang wrote:
> > Yes, there's two choices at the beginning:
> > 1. Using multi-database.
> > 2. Treat lucene database as a single database.
> > Finally, I choose 2. It's a long time ago, I am not quiet sure why this
> > decision is made, maybe:
> > 1. We can handle multiple lucene databases.
>
> That should be possible with multi-databases - you'd just end up with a
> subdatabase for each segment in all of the lucene databases.  If we make
> Xapian::Database's constructor create a Database object with one sub
> database per segment in the Lucene database, this sort of thing should
> just work:
>
>     Xapian::Database db;
>     db.add_database(Xapian::Database("/path/to/lucene1"));
>     db.add_database(Xapian::Database("/path/to/lucene2"));
>     db.add_database(Xapian::Database("/path/to/xapian1"));
>     db.add_database(Xapian::Database("/path/to/xapian2"));
>
> > 2. I am not sure if multi-database can meet the requirements, such as:
> >    Getting a doc_freq(how many documents contains the term) of a
> particular
> > term, actuallly, I want
> >    get sum of doc_freq of a particular term in all lucene segments, I am
> > not sure xapian multi-database do it this way.
>
> A multi-database does sum the "doc_freq" over all subdatabases.
>
> In general, multi-databases act just like a single database with the
> same contents.  There's one exception - when generating an ESet, you
> can ask it to approximate statistics by extrapolating from the first
> sub database rather than summing over all of them, but you can also
> tell it to calculate the exact statistics instead.  This just offers
> a trade-off between speed and exactness.
>
> > Do you think multi-database is a better way to handle lucene database?
>
> I think so - it seems a natural fit.  Sorry for not thinking of this
> earlier.
>
> Cheers,
>     Olly
>
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