lucene-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Tim Smith (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1821) Weight.scorer() not passed doc offset for "sub reader"
Date Mon, 24 Aug 2009 12:25:59 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1821?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12746839#action_12746839
] 

Tim Smith commented on LUCENE-1821:
-----------------------------------

bq. Have you done any benching here? I think we actually found that even most sorting cases
were faster than in 2.4.1.

I haven't done any benchmarking. 
I'm not arguing that 2.9 string sorting is slower than 2.4 string sorting, it may well be
faster for every case.
per segment searching and other improvements potentially added more gains in performance than
the new string sorting added losses in performance.

But, i can say rather confidently, that a large index with a bunch of segments will result
in string sorting being slower when using a per segment string sort cache instead of a full
index sort cache (think worst case using \*:\* query)

bq. loading a field cache off a multi-segment index was dog slow
this is a trade off.
slower cache loading in order to get faster sorting
i plan to provide the ability to do both, and allow specific use cases to decide what is best
for them

> Weight.scorer() not passed doc offset for "sub reader"
> ------------------------------------------------------
>
>                 Key: LUCENE-1821
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1821
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Search
>    Affects Versions: 2.9
>            Reporter: Tim Smith
>             Fix For: 3.1
>
>         Attachments: LUCENE-1821.patch
>
>
> Now that searching is done on a per segment basis, there is no way for a Scorer to know
the "actual" doc id for the document's it matches (only the relative doc offset into the segment)
> If using caches in your scorer that are based on the "entire" index (all segments), there
is now no way to index into them properly from inside a Scorer because the scorer is not passed
the needed offset to calculate the "real" docid
> suggest having Weight.scorer() method also take a integer for the doc offset
> Abstract Weight class should have a constructor that takes this offset as well as a method
to get the offset
> All Weights that have "sub" weights must pass this offset down to created "sub" weights
> Details on workaround:
> In order to work around this, you must do the following:
> * Subclass IndexSearcher
> * Add "int getIndexReaderBase(IndexReader)" method to your subclass
> * during Weight creation, the Weight must hold onto a reference to the passed in Searcher
(casted to your sub class)
> * during Scorer creation, the Scorer must be passed the result of YourSearcher.getIndexReaderBase(reader)
> * Scorer can now rebase any collected docids using this offset
> Example implementation of getIndexReaderBase():
> {code}
> // NOTE: more efficient implementation can be done if you cache the result if gatherSubReaders
in your constructor
> public int getIndexReaderBase(IndexReader reader) {
>   if (reader == getReader()) {
>     return 0;
>   } else {
>     List readers = new ArrayList();
>     gatherSubReaders(readers);
>     Iterator iter = readers.iterator();
>     int maxDoc = 0;
>     while (iter.hasNext()) {
>       IndexReader r = (IndexReader)iter.next();
>       if (r == reader) {
>         return maxDoc;
>       } 
>       maxDoc += r.maxDoc();
>     } 
>   }
>   return -1; // reader not in searcher
> }
> {code}
> Notes:
> * This workaround makes it so you cannot serialize your custom Weight implementation

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.


---------------------------------------------------------------------
To unsubscribe, e-mail: java-dev-unsubscribe@lucene.apache.org
For additional commands, e-mail: java-dev-help@lucene.apache.org


Mime
View raw message