Michael Busch commented on LUCENE-1458:
But it sounds like you're proposing making a strong decoupling of
terms index from terms dict?
Right. Somehow we should genericize the "I don't need the terms
index at all" when opening a SegmentReader. Passing -1 is sort of
hackish. Though I do prefer passing up front your intentions, rather
than loading lazily (LUCENE-1609).
I'm a bit confused. Doesn't the IndexWriter open SegmentReaders
usually with termsIndexDivisor=-1 for merge, and maybe later with
a termsIndexDivisor>0 when IndexWriter#getReader() is called?
That's what I meant with loading lazily.
I thought that's why it'd be good to separate the terms index from
the terms dict. For merge we'd open the dict reader only, and then
if getReader() is called we'd open the terms index reader and give
its reference to the dict reader.
I admit that I didn't follow the NRT changes as closely as I should
have, so I might be missing things here.
> Further steps towards flexible indexing
> Key: LUCENE-1458
> URL: https://issues.apache.org/jira/browse/LUCENE-1458 > Project: Lucene - Java
> Issue Type: New Feature
> Components: Index
> Affects Versions: 2.9
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Priority: Minor
> Attachments: LUCENE-1458.patch, LUCENE-1458.patch, LUCENE-1458.patch, LUCENE-1458.patch, LUCENE-1458.patch, LUCENE-1458.patch
> I attached a very rough checkpoint of my current patch, to get early
> feedback. All tests pass, though back compat tests don't pass due to
> changes to package-private APIs plus certain bugs in tests that
> happened to work (eg call TermPostions.nextPosition() too many times,
> which the new API asserts against).
> [Aside: I think, when we commit changes to package-private APIs such
> that back-compat tests don't pass, we could go back, make a branch on
> the back-compat tag, commit changes to the tests to use the new
> package private APIs on that branch, then fix nightly build to use the
> tip of that branch?o]
> There's still plenty to do before this is committable! This is a
> rather large change:
> * Switches to a new more efficient terms dict format. This still
> uses tii/tis files, but the tii only stores term & long offset
> (not a TermInfo). At seek points, tis encodes term & freq/prox
> offsets absolutely instead of with deltas delta. Also, tis/tii
> are structured by field, so we don't have to record field number
> in every term.
> On first 1 M docs of Wikipedia, tii file is 36% smaller (0.99 MB
> -> 0.64 MB) and tis file is 9% smaller (75.5 MB -> 68.5 MB).
> RAM usage when loading terms dict index is significantly less
> since we only load an array of offsets and an array of String (no
> more TermInfo array). It should be faster to init too.
> This part is basically done.
> * Introduces modular reader codec that strongly decouples terms dict
> from docs/positions readers. EG there is no more TermInfo used
> when reading the new format.
> There's nice symmetry now between reading & writing in the codec
> chain -- the current docs/prox format is captured in:
> FormatPostingsDocsWriter/Reader (.frq file) and
> FormatPostingsPositionsWriter/Reader (.prx file).
> This part is basically done.
> * Introduces a new "flex" API for iterating through the fields,
> terms, docs and positions:
> FieldProducer -> TermsEnum -> DocsEnum -> PostingsEnum
> This replaces TermEnum/Docs/Positions. SegmentReader emulates the
> old API on top of the new API to keep back-compat.
> Next steps:
> * Plug in new codecs (pulsing, pfor) to exercise the modularity /
> fix any hidden assumptions.
> * Expose new API out of IndexReader, deprecate old API but emulate
> old API on top of new one, switch all core/contrib users to the
> new API.
> * Maybe switch to AttributeSources as the base class for TermsEnum,
> DocsEnum, PostingsEnum -- this would give readers API flexibility
> (not just index-file-format flexibility). EG if someone wanted
> to store payload at the term-doc level instead of
> term-doc-position level, you could just add a new attribute.
> * Test performance & iterate.
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