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From "Michael McCandless (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-3838) IndexWriter.maybeMerge() removes deleted documents from index (Lucene 3.1.0 to 3.5.0)
Date Wed, 07 Mar 2012 17:18:58 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-3838?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13224511#comment-13224511
] 

Michael McCandless commented on LUCENE-3838:
--------------------------------------------

bq. of course this happens in version 3.1.0 as stated in the title (in parentheses).

Sorry, what I meant was Lucene has, forever, removed deleted docs
during natural merges (as well as forced merges); I'm not sure why
in 3.0.2 you're seeing otherwise...

bq. Actually, it has never been stated that this is an internal implementation detail (if
I can remember correctly).

I don't know whether this is officially documented anywhere, but it
comes up every so often on the lists and the answer is always "don't
rely on Lucene's docID"... or, rather "rely on docID at your own risk".

bq. Anyway, we already have an ID field but we can't rely on it for long running operations.

I didn't fully understand why you can't use your ID field for long
running operations...

bq. I only don't understand if we will have to wait for a Lucene 4.0 release for a custom
codec implementation 

You'd have to use Lucene trunk (not yet released) to work with codecs.

bq. If I need to implement it for trunk than can you please give me a starting point where
to begin from?

Start here I think?

  http://wiki.apache.org/lucene-java/HowToContribute

EG, get a trunk checkout, browse trunk's javadocs, look @ the test cases, etc.

bq. Also, can this approach differentiate between maybeMerge() and forceMerge().

Maybe... eg a MergePolicy/Scheduler knows if a given merge request was
"forced" or not.

                
> IndexWriter.maybeMerge() removes deleted documents from index (Lucene 3.1.0 to 3.5.0)
> -------------------------------------------------------------------------------------
>
>                 Key: LUCENE-3838
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3838
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: core/index
>    Affects Versions: 3.1, 3.2, 3.3, 3.4, 3.5
>         Environment: Windows, Linux, OSX
>            Reporter: Ivan Stojanovic
>            Priority: Blocker
>              Labels: api-change
>         Attachments: TempTest.java
>
>
> My company uses Lucene for high performance, heavy loaded farms of translation repositories
with hundreds of simultaneous add/delete/update/search/retrieve threads. In order to support
this complex architecture beside other things and tricks used here I rely on docId-s being
unchanged until I ask that explicitly (using IndexWriter.optimize() - IndexWriter.forceMerge()).
> For this behavior LogMergePolicy is used.
> This worked fine until we raised the Lucene version from 3.0.2 to 3.5.0. Until version
3.1.0 merge triggerred by IndexWriter.addDocument() didn't expunge deleted documents ensuring
that docId-s stayed unchanged and making some critical jobs possible without impact on index
size. IndexWriter.optimize() did the actual deleted documents removal.
> From Lucene version 3.1.0 IndexWriter.maybeMerge() does the same thing as IndexWriter.forceMerge()
regarding deleted documents. There is no difference. This leads to unpredictable internal
index structure changes during simple document add (and possible delete) operations and in
undefined point in time. I looked into the Lucene source code and can definitely confirm this.
> This issue makes our Lucene client code totally unusable.
> Solution steps:
> 1) add a flag somewhere that will control whether the deleted documents should be removed
in maybeMerge(). Note that this is only a half of what we need here.
> 2) make forceMerge() always remove deleted documents no matter if maybeMerge() removes
them or not. Alternatively, there can be another parameter added to forceMerge() that will
also tell if deleted documents should be removed from index or not.
> The sample JUnit code that can replicate this issue is added below.
> public class TempTest {
>     private Analyzer _analyzer = new KeywordAnalyzer();
>     @Test
>     public void testIndex() throws Exception {
> 	File indexDir = new File("sample-index");
> 	if (indexDir.exists()) {
> 	    indexDir.delete();
> 	}
> 	FSDirectory index = FSDirectory.open(indexDir);
> 	Document doc;
> 	IndexWriter writer = createWriter(index, true);
> 	try {
> 	    doc = new Document();
> 	    doc.add(new Field("field", "text0", Field.Store.YES,
> 		    Field.Index.ANALYZED));
> 	    writer.addDocument(doc);
> 	    doc = new Document();
> 	    doc.add(new Field("field", "text1", Field.Store.YES,
> 		    Field.Index.ANALYZED));
> 	    writer.addDocument(doc);
> 	    doc = new Document();
> 	    doc.add(new Field("field", "text2", Field.Store.YES,
> 		    Field.Index.ANALYZED));
> 	    writer.addDocument(doc);
> 	    writer.commit();
> 	} finally {
> 	    writer.close();
> 	}
> 	IndexReader reader = IndexReader.open(index, false);
> 	try {
> 	    reader.deleteDocument(1);
> 	} finally {
> 	    reader.close();
> 	}
> 	writer = createWriter(index, false);
> 	try {
> 	    for (int i = 3; i < 100; i++) {
> 		doc = new Document();
> 		doc.add(new Field("field", "text" + i, Field.Store.YES,
> 			Field.Index.ANALYZED));
> 		writer.addDocument(doc);
> 		writer.commit();
> 	    }
> 	} finally {
> 	    writer.close();
> 	}
> 	boolean deleted;
> 	String text;
> 	reader = IndexReader.open(index, true);
> 	try {
> 	    deleted = reader.isDeleted(1);
> 	    text = reader.document(1).get("field");
> 	} finally {
> 	    reader.close();
> 	}
> 	assertTrue(deleted); // This line breaks
> 	assertEquals("text1", text);
>     }
>     private MergePolicy createEngineMergePolicy() {
> 	LogDocMergePolicy mergePolicy = new LogDocMergePolicy();
> 	mergePolicy.setCalibrateSizeByDeletes(false);
> 	mergePolicy.setUseCompoundFile(true);
> 	mergePolicy.setNoCFSRatio(1.0);
> 	return mergePolicy;
>     }
>     private IndexWriter createWriter(Directory index, boolean create)
> 	    throws Exception {
> 	IndexWriterConfig iwConfig = new IndexWriterConfig(Version.LUCENE_35,
> 		_analyzer);
> 	iwConfig.setOpenMode(create ? IndexWriterConfig.OpenMode.CREATE
> 		: IndexWriterConfig.OpenMode.APPEND);
> 	iwConfig.setMergePolicy(createEngineMergePolicy());
> 	iwConfig.setMergeScheduler(new ConcurrentMergeScheduler());
> 	return new IndexWriter(index, iwConfig);
>     }
> }

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