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From Mikhail Khludnev <m...@apache.org>
Subject Re: Terminology. LeafReader -> TermEnum -> PostingsEnum
Date Thu, 14 Dec 2017 15:10:48 GMT
Vadim,
I suppose https://vimeo.com/32065505 is old good explanation of all Lucene
API dimensions.
It covers the most of your questions. FWIW, Leaf is a segment, and postings
is a list of occurrences.
Regarding attributes in postings, iirc it's only used in some suggester,
but now I even can't find this usage.

On Thu, Dec 14, 2017 at 12:15 PM, Vadim Gindin <vgindin@detectum.com> wrote:

> Hi All
>
> I have a question about API. Particularly, about used terminology.
>
> 1. LeafReader. Why it starts with "Leaf"? Can I understand that, that such
> reader is intended for reading only one leaf of index tree? Does it mean
> that it is working inside a context (LeafReaderContext) of several
> documents "physically" located in that leaf?
>
> 2.  Our LeafReader is positioned in some document, and reader.terms(field)
> will return terms list for the single field from the index. Right?
>
> 3. LeafReader is the successor of IndexReader, which has getTermVectors(int
> docID)
> Can I use it in my custom Query (to be aware of all documents fields)
> instead of terms(field)
>
> 4. I.e. LeafReader contains statistical methods, methods returning the
> document values, and the methods returning terms and postings. terms() and
> postings() are intended for search.
>
> 3. What is Postings/PostingEnum? Why is it named starting with "Posting"?
> My native language is Russian and I'm a bit confused trying to find a
> corresponding meaning of this word in a search context.
>
> 5. Ok, I see PostingEnum implements some basic interface DocIdSetIterator,
> but PostingEnum is one of approximately 20 implementations of that
> interface. Why is it used in LeafReader? What the principal difference
> between these 20 implementations and which of them can be really useful?
>
> Regards,
> Vadim Gindin
>



-- 
Sincerely yours
Mikhail Khludnev

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