Marvin Humphrey commented on LUCENE-1458:
> I think, just like we are pushing for column-stride / FieldCache to be
> "per segment" instead of one big merged array, we should move in the
> same direction for searching?
Algorithmically speaking, it would definitely help this specific task, and
that's a BIG FAT PLUS. This, plus memory mapping and writing the DocID -> ord
map at index-time, allows us to totally eliminate the current cost of loading
sort caches at IndexReader startup. The question is, how easy is it to
refactor our search OO hierarchy to support it?
If our goal is minimal impact to the current model, we worry only about the
TopFieldDocs search() method. We can hack in per-segment bookending via doc
number to the hit collection routine, initializing the TopFieldDocCollector
each segment (either creating a new one or popping all the collected docs).
But does it make sense to be more aggressive? Should Searchers run hit
collection against individual segments? Should Scorers only be compiled
against single segments?
Maybe so. I implemented pruning (early termination) in KS, and it had to be
done per segment. This is because you have to sort the documents within a
segment according to the primary criteria you want to prune on (typically doc
boost). I've since ripped out that code because it was adding too much
complexity, but maybe there would have been less complexity if segments were
closer to the foreground.
> 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
> Fix For: 2.9
> Attachments: 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.
This message is automatically generated by JIRA.
You can reply to this email to add a comment to the issue online.