1.Adding documents to an index：
 protected String[] keywords = {"1", "2"};
 protected String[] unindexed = {"Netherlands", "Italy"};
 protected String[] unstored = {"Amsterdam has lots of bridges", "Venice has lots of canals"};
 protected String[] text = {"Amsterdam", "Venice"};
 Directory dir = FSDirectory.getDirectory(indexDir, true);
 IndexWriter writer = new IndexWriter(dir, new SimpleAnalyzer(), true);
 writer.setUseCompoundFile(true);
 for (int i = 0; i < keywords.length; i++) {
  Document doc = new Document();
  doc.add(Field.Keyword("id", keywords[i]));
  doc.add(Field.UnIndexed("country", unindexed[i]));
  doc.add(Field.UnStored("contents", unstored[i]));
  doc.add(Field.Text("city", text[i]));
  writer.addDocument(doc);
 }
 writer.optimize();
 writer.close();
2.Removing Documents from an index：
 IndexReader reader = IndexReader.open(dir);
 reader.delete(1);
上面的方式一次只能刪除一個(gè)document，下面的方法可以刪除多個(gè)滿(mǎn)足條件的document
 IndexReader reader = IndexReader.open(dir);
 reader.delete(new Term("city", "Amsterdam"));
 reader.close();

3.Index dates
 Document doc = new Document();
 doc.add(Field.Keyword("indexDate", new Date()));

4.Tuning indexing performance
 IndexWriter          System property                            Default value          Description
 --------------------------------------------------------------------------------------------------
 mergeFactor          org.apache.lucene.mergeFactor        10       Controls segment merge  frequency and size
 maxMergeDocs     org.apache.lucene.maxMergeDocs   Integar.MAX_VALUE    Limits the number of  documents per segement
 minMergeDocs         org.apache.lucene.minMergeDocs     10     Controls the amount of   RAM used when indexing

mergeFactor控制寫(xiě)入硬盤(pán)前內(nèi)存中緩存的document數(shù)量，同時(shí)控制merge index segments的頻率。其默認(rèn)值是10，即存滿(mǎn)10個(gè)
documents后就必須寫(xiě)入硬盤(pán)，而且如果segment的數(shù)量達(dá)到10的級(jí)數(shù)的時(shí)候會(huì)merge成一個(gè)segment，當(dāng)然maxMergeDocs限制了每個(gè)
segment最大能夠保存的document數(shù)量。mergeFactor越大的話(huà)就越能利用RAM，提高index的效率，但是mergeFactor越高也就意味著
merge的頻率就越低，會(huì)可能導(dǎo)致segments的數(shù)量很大（因?yàn)闆](méi)有merge），這樣search的時(shí)候就需要打開(kāi)更多的segment文件，也就
降低了search的效率。minMergeDocs is another IndexWriter instance variable that affects indexing performance. Its
value controls how many Documents have to be buffered before they’re merged to a segment.也即是說(shuō)minMergeDocs也具有
mergeFactor控制緩存document數(shù)量的功能。

5.RAMDirectory幫助利用RAM，也可以采用集群或者多線程的方式充分利用硬件和軟件資源，提高index的效率。

6.有時(shí)候?qū)τ诿總€(gè)field可能希望控制其大小，比如只對(duì)前1000個(gè)term做index，這個(gè)時(shí)候就需要使用maxFieldLength來(lái)控制。

7.IndexWriter’s optimize()方法就是將segments進(jìn)行merge，降低segments的數(shù)量從而減少search的時(shí)候讀取index的時(shí)間。

8.注意多線程環(huán)境下的工作：an index-modifying IndexReader operation can’t be executed
while an index-modifying IndexWriter operation is in progress.為了防止誤用，Lucene在使用某些API時(shí)會(huì)給
index上鎖。