how to delete documents using term in lucene - java

I am trying to delete a document by using a term in lucene index. but the code that I made below isn't working. are there any suggestion of how can I perform deleting function in lucene index?
public class DocumentDelete {
public static void main(String[] args) {
File indexDir = new File("C:/Users/Raden/Documents/lucene/LuceneHibernate/adi");
Term term = new Term(FIELD_PATH, "compatible");
Directory directory = FSDirectory.getDirectory(indexDir);
IndexReader indexReader = IndexReader.open(directory);
indexReader.deleteDocuments(term);
indexReader.close();
}
}

IndexReader indexReader = IndexReader.open(directory); // this one uses default readonly mode
instead use this:
IndexReader indexReader = IndexReader.open(directory, false); // this will open the index in edit mode and you can delete the index. . .
So you do not need any extra tool for deleting index contents. . .

Related

Unable to identify error in Lucene MoreLikeThis

I need to use Lucene MoreLikeThis to find similar documents given a paragraph of text. I am new to Lucene and followed the code here
I have already indexed the documents at the directory - "C:\Users\lucene_index_files\v2"
I am using "They are computer engineers and they like to develop their own tools. The program in languages like Java, CPP." as the document to which I want to find similar documents.
public class LuceneSearcher2 {
public static void main(String[] args) throws IOException {
LuceneSearcher2 m = new LuceneSearcher2();
System.out.println("1");
m.start();
System.out.println("2");
//m.writerEntries();
m.findSilimar("They are computer engineers and they like to develop their own tools. The program in languages like Java, CPP.");
System.out.println("3");
}
private Directory indexDir;
private StandardAnalyzer analyzer;
private IndexWriterConfig config;
public void start() throws IOException{
//analyzer = new StandardAnalyzer(Version.LUCENE_42);
//config = new IndexWriterConfig(Version.LUCENE_42, analyzer);
analyzer = new StandardAnalyzer();
config = new IndexWriterConfig(analyzer);
config.setOpenMode(OpenMode.CREATE_OR_APPEND);
indexDir = new RAMDirectory(); //don't write on disk
//https://stackoverflow.com/questions/36542551/lucene-in-java-method-not-found?rq=1
indexDir = FSDirectory.open(FileSystems.getDefault().getPath("C:\\Users\\lucene_index_files\\v2")); //write on disk
//System.out.println(indexDir);
}
private void findSilimar(String searchForSimilar) throws IOException {
IndexReader reader = DirectoryReader.open(indexDir);
IndexSearcher indexSearcher = new IndexSearcher(reader);
System.out.println("2a");
MoreLikeThis mlt = new MoreLikeThis(reader);
mlt.setMinTermFreq(0);
mlt.setMinDocFreq(0);
mlt.setFieldNames(new String[]{"title", "content"});
mlt.setAnalyzer(analyzer);
System.out.println("2b");
StringReader sReader = new StringReader(searchForSimilar);
//Query query = mlt.like(sReader, null);
//Throws error - The method like(String, Reader...) in the type MoreLikeThis is not applicable for the arguments (StringReader, null)
Query query = mlt.like("computer");
System.out.println("2c");
System.out.println(query.toString());
TopDocs topDocs = indexSearcher.search(query,10);
for ( ScoreDoc scoreDoc : topDocs.scoreDocs ) {
Document aSimilar = indexSearcher.doc( scoreDoc.doc );
String similarTitle = aSimilar.get("title");
String similarContent = aSimilar.get("content");
System.out.println("====similar finded====");
System.out.println("title: "+ similarTitle);
System.out.println("content: "+ similarContent);
}
System.out.println("2d");
}}
I am unsure as to what is causing the system to not generate an output/
What is your output ? I am assuming your not finding similar documents. The reason could be that the query you are creating is empty.
First of all to run your code in a meaningful way this line
Query query = mlt.like(sReader, null);
needs a String[] of field names as the argument, so it should work like this
Query query = mlt.like(sReader, new String[]{"title", "content"});
Now, in order to use MoreLikeThis in Lucene, your stored Fields have to have the set the option to store term vectors "setStoreTermVectors(true);" true when creating fields, for instance like this:
FieldType fieldType = new FieldType();
fieldType.setStored(true);
fieldType.setStoreTermVectors(true);
fieldType.setTokenized(true);
Field contentField = new Field("contents", this.getBlurb(), fieldType);
doc.add(contentField);
Leaving this out could result in an empty query string and consequently no results for the query

Lucene can't find documents after update

It seems that whenever I update an existing document in the index (same behavior for delete / add), it can't be found with a TermQuery. Here's a short snippet:
iw = new IndexWriter(directory, config);
Document doc = new Document();
doc.add(new StringField("string", "a", Store.YES));
doc.add(new IntField("int", 1, Store.YES));
iw.addDocument(doc);
Query query = new TermQuery(new Term("string","a"));
Document[] hits = search(query);
doc = hits[0];
print(doc);
doc.removeField("int");
doc.add(new IntField("int", 2, Store.YES));
iw.updateDocument(new Term("string","a"), doc);
hits = search(query);
System.out.println(hits.length);
System.out.println("_________________");
for(Document hit : search(new MatchAllDocsQuery())){
print(hit);
}
This produces the following console output:
stored,indexed,tokenized,omitNorms,indexOptions=DOCS_ONLY<string:a>
stored<int:1>
________________
0
_________________
stored,indexed,tokenized,omitNorms,indexOptions=DOCS_ONLY<string:a>
stored<int:2>
________________
It seems that after the update, the document (rather the new document) in the index and gets returned by the MatchAllDocsQuery, but can't be found by a TermQuery.
Full sample code available at http://pastebin.com/sP2Vav9v
Also, this only happens (second search not working) when the StringField value contains special characters (e.g. file:/F:/).
The code which you have referenced in pastebin doesn't find anything because your StringField is nothing but a stopword (a). Replacing a with something which is not a stopword (e.g. ax) makes both searches to return 1 doc.
You would also achieve the correct result if you were to construct StandardAnalyzer with empty stopword set (CharArraySet.EMPTY_SET) yet still using a for StringField. This wouldn't work for file:/F:/ though.
However, the best solution is this case would be to replace StandardAnalyzer with KeywordAnalyzer.
I could get rid of this by recreating my working directory after all indexing operations :
create a new directory just for this indexing operations named "path_dir" for example. If you have updated then call the following operations and do all of your previous works again.
StandardAnalyzer analyzer = new StandardAnalyzer(Version.LUCENE_46);
FSDirectory dir;
try {
// delete indexing files :
dir = FSDirectory.open(new File(path_dir));
IndexWriterConfig config = new IndexWriterConfig(Version.LUCENE_46, analyzer);
IndexWriter writer = new IndexWriter(dir, config);
writer.deleteAll();
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
However, note that this way will be very slow if you are handling big data.

Do you need a new instance of IndexReader and IndexSearcher every time?

In a web application, I'm having one IndexReader and one respective IndexSearcher for the whole application.
The documentation says they are thread-safe, so that's ok, but is it supposed to work properly if the underlying index changes (e.g. an IndexWriter makes changes)?
Yes, you need to reopen the reader.
Use the SearcherManager to automatically update the reader, calling maybeRefresh when you've made changes.
Samples of Scala code below:
#volatile protected var LAST_SEARCHER_REFRESH = 0
protected lazy val SEARCHER_MANAGER = new SearcherManager (LUCENE_DIR, new SearcherFactory {
override def newSearcher (reader: IndexReader): IndexSearcher = {new IndexSearcher (reader)}
})
...
if (LAST_SEARCHER_REFRESH != Time.relativeSeconds()) {LAST_SEARCHER_REFRESH = Time.relativeSeconds(); SEARCHER_MANAGER.maybeRefresh()}
val searcher = SEARCHER_MANAGER.acquire(); try {
searcher.search (query, collector)
...
} finally {SEARCHER_MANAGER.release (searcher)}
Sometimes you'll have to implement your own caching though, like when you need to synchronize the IndexReader with TaxonomyReader. IndexSearcher description has recommendations about how to do that (there is a fast path via DirectoryReader.open(IndexWriter, applyAllDeletes) to make a new reader from a writer used to commit the changes).

how to search a file with lucene

I want to do a search for a query within a file "fdictionary.txt" containing a list of words (230,000 words) written line by line. any suggestion why this code is not working?
The spell checking part is working and gives me the list of suggestions (I limited the length of the list to 1). what I want to do is to search that fdictionary and if the word is already in there, do not call spell checking. My Search function is not working. It does not give me error! Here is what I have implemented:
public class SpellCorrection {
public static File indexDir = new File("/../idxDir");
public static void main(String[] args) throws IOException, FileNotFoundException, CorruptIndexException, ParseException {
Directory directory = FSDirectory.open(indexDir);
SpellChecker spell = new SpellChecker(directory);
IndexWriterConfig config = new IndexWriterConfig(Version.LUCENE_20, null);
File dictionary = new File("/../fdictionary00.txt");
spell.indexDictionary(new PlainTextDictionary(dictionary), config, true);
String query = "red"; //kne, console
String correctedQuery = query; //kne, console
if (!search(directory, query)) {
String[] suggestions = spell.suggestSimilar(query, 1);
if (suggestions != null) {correctedQuery=suggestions[0];}
}
System.out.println("The Query was: "+query);
System.out.println("The Corrected Query is: "+correctedQuery);
}
public static boolean search(Directory directory, String queryTerm) throws FileNotFoundException, CorruptIndexException, IOException, ParseException {
boolean isIn = false;
IndexReader indexReader = IndexReader.open(directory);
IndexSearcher indexSearcher = new IndexSearcher(indexReader);
Analyzer analyzer = new StandardAnalyzer(Version.LUCENE_20);
Term term = new Term(queryTerm);
Query termQuery = new TermQuery(term);
TopDocs hits = indexSearcher.search(termQuery, 100);
System.out.println(hits.totalHits);
if (hits.totalHits > 0) {
isIn = true;
}
return isIn;
}
}
where are you indexing the content from fdictionary00.txt?
You can search using IndexSearcher, only when you have index. If you are new to lucene, you might want to check some quick tutorials. (like http://lucenetutorial.com/lucene-in-5-minutes.html)
You never built the index.
You need to setup the index...
Directory directory = FSDirectory.open(indexDir);
Analyzer analyzer = new StandardAnalyzer(Version.LUCENE_20);
IndexWriter writer = new IndexWriter(directory,analyzer,true,IndexWriter.MaxFieldLength.UNLIMITED );
You then need to create a document and add each term to the document as an analyzed field..
Document doc = new Document();
doc.Add(new Field("name", word , Field.Store.YES, Field.Index.ANALYZED));
Then add the document to the index
writer.AddDocument(doc);
writer.Optimize();
Now build the index and close the index writer.
writer.Commit();
writer.Close();
You could make your SpellChecker instance available in a service and use spellChecker.exist(word).
Be aware that the SpellChecker will not index words 2 characters or less. To get around this you can add them to the index after you have created it (add them into SpellChecker.F_WORD field).
If you want to add to your live index and make them available for exist(word) then you will need to add them to the SpellChecker.F_WORD field. Of course, because you're not adding to all the other fields such as gram/start/end etc then your word will not appear as a suggestion for other misspelled words.
In this case you'd have had to add the word into your file so when you re-create the index it would then be available as a suggestion. It would be great if the project made SpellChecker.createDocument(...) public/protected, rather than private, as this method accomplishes everything with adding words.
After all this your need to call spellChecker.setSpellIndex(directory).

Lucene Java opening too many files. Am I using IndexWriter properly?

My Lucene Java implementation is eating up too many files. I followed the instructions in the Lucene Wiki about too many open files, but that only helped slow the problem. Here is my code to add objects (PTicket) to the index:
//This gets called when the bean is instantiated
public void initializeIndex() {
analyzer = new WhitespaceAnalyzer(Version.LUCENE_32);
config = new IndexWriterConfig(Version.LUCENE_32, analyzer);
}
public void addAllToIndex(Collection<PTicket> records) {
IndexWriter indexWriter = null;
config = new IndexWriterConfig(Version.LUCENE_32, analyzer);
try{
indexWriter = new IndexWriter(directory, config);
for(PTicket record : records) {
Document doc = new Document();
StringBuffer documentText = new StringBuffer();
doc.add(new Field("_id", record.getIdAsString(), Field.Store.YES, Field.Index.ANALYZED));
doc.add(new Field("_type", record.getType(), Field.Store.YES, Field.Index.ANALYZED));
for(String key : record.getProps().keySet()) {
List<String> vals = record.getProps().get(key);
for(String val : vals) {
addToDocument(doc, key, val);
documentText.append(val).append(" ");
}
}
addToDocument(doc, DOC_TEXT, documentText.toString());
indexWriter.addDocument(doc);
}
indexWriter.optimize();
} catch (Exception e) {
e.printStackTrace();
} finally {
cleanup(indexWriter);
}
}
private void cleanup(IndexWriter iw) {
if(iw == null) {
return;
}
try{
iw.close();
} catch (IOException ioe) {
logger.error("Error trying to close index writer");
logger.error("{}", ioe.getClass().getName());
logger.error("{}", ioe.getMessage());
}
}
private void addToDocument(Document doc, String field, String value) {
doc.add(new Field(field, value, Field.Store.YES, Field.Index.ANALYZED));
}
EDIT TO ADD code for searching
public Set<Object> searchIndex(AthenaSearch search) {
try {
Query q = new QueryParser(Version.LUCENE_32, DOC_TEXT, analyzer).parse(query);
//search is actually instantiated in initialization. Lucene recommends this.
//IndexSearcher searcher = new IndexSearcher(directory, true);
TopDocs topDocs = searcher.search(q, numResults);
ScoreDoc[] hits = topDocs.scoreDocs;
for(int i=start;i<hits.length;++i) {
int docId = hits[i].doc;
Document d = searcher.doc(docId);
ids.add(d.get("_id"));
}
return ids;
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
This code is in a web application.
1) Is this the advised way to use IndexWriter (instantiating a new one on each add to index)?
2) I've read that raising ulimit will help, but that just seems like a band-aid that won't address the actual problem.
3) Could the problem lie with IndexSearcher?
1) Is this the advised way to use
IndexWriter (instantiating a new one
on each add to index)?
i advise No, there are constructors, which will check if exists or create a new writer, in the directory containing the index. problem 2 would be solved if you reuse the indexwriter.
EDIT:
Ok it seems in Lucene 3.2 the most but one constructors are deprecated,so the resue of Indexwriter can be achieved by using Enum IndexWriterConfig.OpenMode with value CREATE_OR_APPEND.
also, opening new writer and closing on each document add is not efficient,i suggest reuse, if you want to speed up indexing, set the setRamBufferSize default value is 16MB, so do it by trial and error method
from the docs:
Note that you can open an index with
create=true even while readers are
using the index. The old readers will
continue to search the "point in time"
snapshot they had opened, and won't
see the newly created index until they
re-open.
also reuse the IndexSearcher,i cannot see the code for searching, but Indexsearcher is threadsafe and can be used as Readonly as well
also i suggest you to use MergeFactor on writer, this is not necessary but will help on limiting the creation of inverted index files, do it by trial and error method
I think we'd need to see your search code to be sure, but I'd suspect that it is a problem with the index searcher. More specifically, make sure that your index reader is being properly closed when you've finished with it.
Good luck,
The scientific correct answer would be: You can't really tell by this fragment of code.
The more constructive answer would be:
You have to make sure that there is only one IndexWriter is writing to the index at any given time and you therefor need some mechanism to make sure of that. So my answer depends of what you want to accomplish:
do you want a deeper understanding of Lucene? or..
do you just want to build and use an index?
If you answer is the latter, you probably want to look at projects like Solr, which hides all the index reading and writing.
This question is probably a duplicate of
Too many open files Error on Lucene
I am repeating here my answer for that.
Use compound index to reduce file count. When this flag is set, lucene will write a segment as single .cfs file instead of multiple files. This will reduce the number of files significantly.
IndexWriter.setUseCompoundFile(true)

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