From 9f973b6988e82d1afe3c963879022cbd3c843e3f Mon Sep 17 00:00:00 2001
From: Michael McCandless <mikemccand@apache.org>
Date: Wed, 19 May 2010 18:37:21 +0000
Subject: [PATCH] add comment

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@946330 13f79535-47bb-0310-9956-ffa450edef68
---
 lucene/src/java/org/apache/lucene/index/IndexWriter.java | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lucene/src/java/org/apache/lucene/index/IndexWriter.java b/lucene/src/java/org/apache/lucene/index/IndexWriter.java
index a3baa2e2b37..2833f6533df 100644
--- a/lucene/src/java/org/apache/lucene/index/IndexWriter.java
+++ b/lucene/src/java/org/apache/lucene/index/IndexWriter.java
@@ -4401,6 +4401,15 @@ public class IndexWriter implements Closeable {
       if (mergeDocStores && !merge.mergeDocStores) {
         merge.mergeDocStores = true;
         synchronized(this) {
+
+          // If 1) we must now merge doc stores, and 2) at
+          // least one of the segments we are merging uses
+          // the doc store we are now writing to, we must at
+          // this point force this doc store closed (by
+          // calling flush).  If we didn't do this then the
+          // readers will attempt to open an IndexInput
+          // on files that have still-open IndexOutputs
+          // against them:
           if (dss.contains(docWriter.getDocStoreSegment())) {
             if (infoStream != null)
               message("now flush at mergeMiddle");