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From Vadim Gindin <vgin...@detectum.com>
Subject Terminology. LeafReader -> TermEnum -> PostingsEnum
Date Thu, 14 Dec 2017 09:15:52 GMT
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

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