solr performance settings

the target of these performance settings is the reduction of IO in
general and during search in particual.
- reduced mergeFactor to 4. This will increase the IO during indexing,
but will reduce IO during search. It will also greatly reduce the number
of open files which should make it possible to have overall larger
indexes until the number of open files in an OS is reached.
- increased ramBufferSizeMB to 256mb. This will reduce the number of
commits. This change may compensate the reduction of the mergeFactor.
- disabled updateLog. This is a real-time search feature which is
available in YaCy anyway because a commit is forced if index.html is
called. The updateLog feature causes a lot of IO during indexing and
search and produced a lot of files in SEGMENTS/solr_40/data/tlog

defaults/solr/solrconfig.xml

@@ -149,7 +149,7 @@
          before flushing.
          If both ramBufferSizeMB and maxBufferedDocs is set, then
          Lucene will flush based on whichever limit is hit first.  -->
-        <!-- <ramBufferSizeMB>32</ramBufferSizeMB> -->
+        <!-- <ramBufferSizeMB>256</ramBufferSizeMB> -->
         <!-- <maxBufferedDocs>1000</maxBufferedDocs> -->
         
         <!-- Expert: Merge Policy
@@ -174,7 +174,7 @@
          Default is 10 for both merge policies.
          -->
         <!--
-         <mergeFactor>10</mergeFactor>
+         <mergeFactor>4</mergeFactor>
          -->
         
         <!-- Expert: Merge Scheduler
@@ -368,10 +368,11 @@
         <!-- Enables a transaction log, currently used for real-time get.
          "dir" - the target directory for transaction logs, defaults to the
          solr data directory.  -->
+        <!--
         <updateLog>
             <str name="dir">${solr.data.dir:}</str>
         </updateLog>
-        
+        -->
         
     </updateHandler>