[Solr Wiki] Update of "SolrPerformanceFactors" by YonikSeeley

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The following page has been changed by YonikSeeley:
http://wiki.apache.org/solr/SolrPerformanceFactors

The comment on the change is:
correct description of mergeFactor

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  The mergeFactor roughly determines the number of segments.
   
- The mergeFactor value tells Lucene how many documents to store in memory before writing them to disk, as well as how often to merge multiple segments. With the default value of 10, Lucene will store 10 documents in memory before writing them to a single segment on the disk. 
+ The mergeFactor value tells Lucene how many segments of equal size to build before merging them into a single segment.  It can be thought of as the base of a number system.
  
- For example, if you set mergeFactor to 10, a new segment will be created on the disk for every 10 documents added to the index. When the 10th segment of size 10 is added, all 10 will be merged into a single segment of size 100. When 10 such segments of size 100 have been added, they will be merged into a single segment containing 1000 documents, and so on. Therefore, at any time, there will be no more than 9 segments in each  index size.
+ For example, if you set mergeFactor to 10, a new segment will be created on the disk for every 1000 (or maxBufferedDocs) documents added to the index. When the 10th segment of size 1000 is added, all 10 will be merged into a single segment of size 10,000. When 10 such segments of size 10,000 have been added, they will be merged into a single segment containing 100,000 documents, and so on. Therefore, at any time, there will be no more than 9 segments in each  index size.
   
  These values are set in the *mainIndex* section of solrconfig.xml (disregard the indexDefaults section):   
  
@@ -32, +32 @@

     * Con: Less frequent merges, resulting in a collection with more index files which may slow searching
  
  Low value merge factor (e.g., 2):
-    * Pro: Smaller number of index files, which speeds up searching. Index more-up-to-date 
+    * Pro: Smaller number of index files, which speeds up searching.
     * Con: More segment merges slow down indexing.
  
  === HashDocSet Max Size Considerations ===