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From Shai Erera <ser...@gmail.com>
Subject Re: Fields, Index segments and docIds (second Try)
Date Wed, 30 Apr 2014 08:48:49 GMT
I hope I got all the details right, if I didn't then please clarify. Also,
I haven't read the entire thread, so if someone already suggested this ...
well, it probably means it's the right solution :)

It sounds like you could use Lucene's ParallelCompositeReader, which
already handles multiple IndexReaders that are aligned by their internal
document IDs. The way it would work, as far as I understand your scenario
is something like the following table (columns denote different indexes).
Each index contains a subset of relevant fields, where common contains the
common fields, and each language index contains the respective language
fields.

DocID        LuceneID  Common  English       German        ....
"FirstDoc"   0         A,B,C   EN_words,     DE_words,
                               EN_sentences  DE_sentences
"SecondDoc"  1         A,B,C
"ThirdDoc"   2         A,B,C

Each index can contain all relevant fields, or only a subset (e.g. maybe
not all documents have a value for the 'B' field in the 'common' index).
What's absolutely very important here though is that the indexes are
created very carefully, and if e.g. SecondDoc is not translated into
German, *you must still have an empty document* in the German index, or
otherwise, document IDs will not align.

Lucene does not offer a way to build those indexes though (patches
welcome!!). We've started some effort very long time ago on LUCENE-1879
(there's a patch and a discussion for an alternative approach) as well as
there is a very useful suggestion in ParallelCompositeReader's jdocs (use
LogDocMergePolicy).

One challenge is how to support multi-threaded indexing, but perhaps this
isn't a problem in your application? It sounds like, by you writing that a
user will "download the german index", that the indexes are built offline?

Another challenge is how to control segment merging, so that the *exact
same segments* are merged over the parallel indexes. Again, if your
application builds the indexes offline, then this should be easier to
accomplish.

I assume though that when you index e.g. the German documents, then the
already indexes 'common' fields do not change for a document. If they do,
you will need to rebuild the 'common' index too.

Once you achieve a correct parallel index, it is very easy to open a
ParallelCompositeReader on any subset of the indexes, e.g. Common+English,
Common+German, or Common+English+German and search it, since the internal
document IDs are perfectly aligned.

Shai


On Wed, Apr 30, 2014 at 7:07 AM, Jose Carlos Canova <
jose.carlos.canova@gmail.com> wrote:

> My suggestion is you not worry about the docId, in practice it is an
> "internal lucene" id, quite similar with a rowId on a database, each index
> may generate a different docId (it is their problem) from a translated
> document, you may use your own ID that relates one document to another on
> different index mainly because like you mention are translated documents
> that on theory can be ranked differently from language to language (it is
> not an obligation that a set of documents on different languages spams the
> same rank order but i am not 100% sure about this),
>
> Second reason is that 'they may change the internal structure of lucene
> without warrant', and then you lose the forward compatibility.
>
> I am not an expert on Lucene like Schindler, but reading their
> documentation understood that they have a special attention on
> "internal lucene" and "experimental lucene" which means internal is "non
> warrant compatible", and experimental "may be removed".
>
> For example they (apache-lucene) discover a "new manner" to relate each
> document that is more efficient and change some mechanism, then your
> application uses an internal mechanism that is high coupled with lucene
> version xxx (marked as "internal-lucene") you can stuck on a specific
> version and   on future have to rewrite some code because and this might
> cause some "management conflict" if your project follows a continuous
> integration and you are subordinated on a management structure (bad to
> you).
>
> I saw this on several projects that uses Lucene around they do not upgrade
> their lucene components on their new releases one example if i am not wrong
> still uses Lucene 3 and other that i saw around (e.g. Luke) which means
> that "The project was abandoned because the manner how they integrate with
> Lucene was not fully functional".
>
> Another interesting thing is that developing around Lucene is more
> effective, you guarantee that your product will work and they guarantee
> that Lucene works too. This is related with design by contract.
>
> Regards.
>
>
>
>
>
>
>
> On Tue, Apr 29, 2014 at 7:11 PM, Olivier Binda <olivier.binda@wanadoo.fr
> >wrote:
>
> > Hello.
> >
> > Sorry to bring this up again. I don't want to be rudeand I mean no
> > disrespect, but after thinking it through today,
> > I need to and would really love to have the answer to the following
> > question :
> >
> > 1) At lucene indexing time, is it possible to rewrite a read-only index
> so
> > that some fields are only found in some segments (and how ?)
> >
> >
> > Uwe Schindler suggested using different index and a MultiReader for my
> > needs and It probably answers my second question, better formulated as
> "Is
> > it possible to restrict  an index to some of it's segments ? " as a
> > CompositeReader with AtomicReaders (or a custom Directory) that read the
> > aforementioned segments might do the trick
> >
> > Yet, if I am not mistaken (please tell me if I am wrong), it doesn't
> solve
> > my needs as I have around 300000 documents of the following kind :
> >
> > READ ONLY Document :
> > // common fields shipped with the App that aren't language related
> > A:
> > B:
> > C:
> > // fields shipped with the English package (a zip)
> > EN:
> > EN_Words:
> > EN_Sentences:
> > some DocValues
> > // fields shipped with the German package (a zip)
> > DE:
> > DE_Words:
> > DE_Sentences:
> > some DocValues
> > ...
> > There might be hundreds of language package that my users might use
> >
> >
> > If I use different indexes
> > indexA for the common stuff,
> > indexEN for the English package,
> > indexDE for the german package,
> >
> > For sure, I will be able to make a big index out of those by using a
> > MultiReader
> > BUT it really makes an union out of the three index (right ?) which means
> > I'll have 900000 documents
> > and the documents in the indexA won't have any relations to the documents
> > in indexEN (right ?) except if I give each document an id in each index
> and
> > make a join at query time which is a big no no, because I use a
> queryParser
> > and users may enter queries like "A:gah AND (DE:schlaffen OR EN:sleep)"
> >
> > Or I am mistaken and there is a way to create a document in three
> > different index that stay in relations with the same docId ?
> >
> >
> > My solution if question 1 is possible :
> >
> > In contrast, if I am able to build my index so that my READ ONLY Document
> > are stored in
> >
> > SEGMENT 1
> > // common fields shipped with the App that aren't language related
> > A:
> > B:
> > C:
> >
> > SEGMENT 2
> > // fields shipped with the English package (a zip)
> > EN:
> > EN_Words:
> > EN_Sentences:
> > some DocValues
> >
> > SEGMENT 3
> > // fields shipped with the German package (a zip)
> > DE:
> > DE_Words:
> > DE_Sentences:
> > some DocValues
> >
> >
> > I only need to ship SEGMENT 1 in the App and let users download SEGMENT 2
> > or SEGMENT 3 whether they want english or german
> > and use a composite reader with atomic readers (right ?) to use my
> > frankenstein index at query time with a queryparser
> >
> >
> > Also, In case question 1 is possible. I would really like to know too, if
> > it is possible to remap at build time docIds in a read-only index.
> > An application of this would be :
> >
> > At day 1, I shipp my app with 2 languages packages : English and german
> > (documents are uniquely identified by a docId... or by an external id
> > (thanks to a docId<-> external id map)
> >
> > At day 2, I ship an additional language package (French) because I'm able
> > to build an index with English, German, French with the same exact docIds
> > for each document that the index shipped at day 1
> >
> >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: java-user-unsubscribe@lucene.apache.org
> > For additional commands, e-mail: java-user-help@lucene.apache.org
> >
> >
>

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