Index: lucene/CHANGES.txt
===================================================================
--- lucene/CHANGES.txt	(revision 1063734)
+++ lucene/CHANGES.txt	(working copy)
@@ -371,6 +371,9 @@
 * LUCENE-1846: DateTools now uses the US locale everywhere, so DateTools.round()
   is safe also in strange locales.  (Uwe Schindler)
 
+* LUCENE-2891: IndexWriterConfig did not accept -1 in setReaderTermIndexDivisor,
+  which can be used to prevent loading the term infos into memory. (Shai Erera)
+
 New features
 
 * LUCENE-2128: Parallelized fetching document frequencies during weight
Index: lucene/src/test/org/apache/lucene/index/RandomIndexWriter.java
===================================================================
--- lucene/src/test/org/apache/lucene/index/RandomIndexWriter.java	(revision 1063734)
+++ lucene/src/test/org/apache/lucene/index/RandomIndexWriter.java	(working copy)
@@ -148,7 +148,9 @@
         System.out.println("RIW.getReader: open new reader");
       }
       w.commit();
-      return IndexReader.open(w.getDirectory(), new KeepOnlyLastCommitDeletionPolicy(), r.nextBoolean(), _TestUtil.nextInt(r, 1, 10));
+      int termIndexDivisor = _TestUtil.nextInt(r, 0, 10);
+      if (termIndexDivisor == 0) termIndexDivisor = -1; // disable loading term infos
+      return IndexReader.open(w.getDirectory(), new KeepOnlyLastCommitDeletionPolicy(), r.nextBoolean(), termIndexDivisor);
     }
   }
 
Index: lucene/src/test/org/apache/lucene/index/TestIndexWriterConfig.java
===================================================================
--- lucene/src/test/org/apache/lucene/index/TestIndexWriterConfig.java	(revision 1063734)
+++ lucene/src/test/org/apache/lucene/index/TestIndexWriterConfig.java	(working copy)
@@ -230,6 +230,23 @@
       // this is expected
     }
 
+    // Test setReaderTermInfosDivisor
+    try {
+      conf.setReaderTermsIndexDivisor(0);
+      fail("should not have succeeded to set termInfosDivisor to 0");
+    } catch (IllegalArgumentException e) {
+      // this is expected
+    }
+    
+    // Setting to -1 is ok
+    conf.setReaderTermsIndexDivisor(-1);
+    try {
+      conf.setReaderTermsIndexDivisor(-2);
+      fail("should not have succeeded to set termInfosDivisor to < -1");
+    } catch (IllegalArgumentException e) {
+      // this is expected
+    }
+    
     assertEquals(IndexWriterConfig.DEFAULT_MAX_THREAD_STATES, conf.getMaxThreadStates());
     conf.setMaxThreadStates(5);
     assertEquals(5, conf.getMaxThreadStates());
Index: lucene/src/test/org/apache/lucene/util/LuceneTestCase.java
===================================================================
--- lucene/src/test/org/apache/lucene/util/LuceneTestCase.java	(revision 1063734)
+++ lucene/src/test/org/apache/lucene/util/LuceneTestCase.java	(working copy)
@@ -641,7 +641,9 @@
     }
     
     c.setReaderPooling(r.nextBoolean());
-    c.setReaderTermsIndexDivisor(_TestUtil.nextInt(r, 1, 4));
+    int termIndexDivisor = _TestUtil.nextInt(r, 0, 4);
+    if (termIndexDivisor == 0) termIndexDivisor = -1; // disable loading term infos
+    c.setReaderTermsIndexDivisor(termIndexDivisor);
     return c;
   }
 
Index: lucene/src/java/org/apache/lucene/index/IndexWriterConfig.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/IndexWriterConfig.java	(revision 1063734)
+++ lucene/src/java/org/apache/lucene/index/IndexWriterConfig.java	(working copy)
@@ -539,10 +539,11 @@
   /** Sets the term index divisor passed to any readers that
    *  IndexWriter opens, for example when apply deletes or
    *  creating a near-real-time reader in {@link
-   *  IndexWriter#getReader}. */
+   *  IndexWriter#getReader}. If you pass -1, the term infos 
+   *  won't be loaded by the readers. */
   public IndexWriterConfig setReaderTermsIndexDivisor(int divisor) {
-    if (divisor <= 0) {
-      throw new IllegalArgumentException("divisor must be >= 1 (got " + divisor + ")");
+    if (divisor <= 0 && divisor != -1) {
+      throw new IllegalArgumentException("divisor must be >= 1, or -1 (got " + divisor + ")");
     }
     readerTermsIndexDivisor = divisor;
     return this;