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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1458) Further steps towards flexible indexing
Date Mon, 23 Nov 2009 13:40:39 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1458?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12781401#action_12781401
] 

Michael McCandless commented on LUCENE-1458:
--------------------------------------------

bq. perhaps it would help convince you if i instead wrote the code as .terms("𩬅".charAt(0));

I realize a java String can easily contain an unpaired surrogate (eg,
your test case) since it operates in code units not code points, but,
that's not valid unicode, right?

I mean you can't in general send such a string off to a library that
works w/ unicode (like Lucene) and expect the behavior to be well
defined.  Yes, it's neat that Lucene allows that today, but I don't
see that it's "supposed to".

When we encounter an unpaired surrogate during indexing, we replace it
w/ the replacement char.  Why shouldn't we do the same when
searching/reading the index?

What should we do during searching if the unpaired surrogate is inside
the string (not at the end)?  Why should that be different?

bq. Please read Ch2 and 3 of the unicode standard if you want to do this.

Doesn't this apply here?  In "3.2 Conformance"
(http://www.unicode.org/versions/Unicode5.0.0/ch03.pdf) is this first
requirement (C1):

  * A process shall not interpret a high-surrogate code point or a
    low-surrogate code point as an abstract character.

bq. I hope you can start to see how many east asian applications will break because of this.

But how would a search application based on an east asian language
actually create such a term?  In what situation would an unpaired
surrogate find its way down to TermEnum?

Eg when users enter searches, they enter whole unicode chars (code
points) at once (not code units / unpaired surrogates)?  I realize an
app could programmatically construct eg a PrefixQuery that has an
unpaired surrogate... but couldn't they just as easily pair it up
before sending it to Lucene?

bq.  i have applications that will break because of this.

OK, can you shed some more light on how/when your apps do this?


> 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-back-compat.patch, LUCENE-1458-back-compat.patch, LUCENE-1458-back-compat.patch,
LUCENE-1458-back-compat.patch, LUCENE-1458-back-compat.patch, LUCENE-1458-back-compat.patch,
LUCENE-1458.patch, LUCENE-1458.patch, LUCENE-1458.patch, LUCENE-1458.patch, LUCENE-1458.patch,
LUCENE-1458.patch, LUCENE-1458.patch, LUCENE-1458.patch, LUCENE-1458.patch, LUCENE-1458.patch,
LUCENE-1458.patch, LUCENE-1458.patch, LUCENE-1458.patch, LUCENE-1458.tar.bz2, LUCENE-1458.tar.bz2,
LUCENE-1458.tar.bz2, LUCENE-1458.tar.bz2, LUCENE-1458.tar.bz2, LUCENE-1458.tar.bz2, LUCENE-1458.tar.bz2,
UnicodeTestCase.patch, UnicodeTestCase.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:
> {code}
> FormatPostingsTermsDictWriter/Reader
> FormatPostingsDocsWriter/Reader (.frq file) and
> FormatPostingsPositionsWriter/Reader (.prx file).
> {code}
>     This part is basically done.
>   * Introduces a new "flex" API for iterating through the fields,
>     terms, docs and positions:
> {code}
> FieldProducer -> TermsEnum -> DocsEnum -> PostingsEnum
> {code}
>     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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