added store level throttling setting to data import

best practice

docs/best_practice/data_import.txt

@@ -159,6 +159,27 @@ a reasonable value (time in ms)::
   - :ref:`refresh_data`
   - :ref:`sql_ref_refresh_interval`
 
+Store Level Throttling
+.......................
+
+If you do not need to query your data during import, which is the case
+most of the time, you can change the storage policy of how Lucene indices
+are merged. Since merging may affect IO performance, turning merging off
+by setting the ``indices.store.throttle.type`` to ``none`` can help
+to improve indexing performance.
+
+::
+
+  cr> SET GLOBAL TRANSIENT indices.store.throttle.type = 'none';
+  SET OK (... sec)
+
+However if you want to keep merging turned on during import you can
+throttle the merge operation by decreasing the maximum bytes per second
+(default ``20mb``)::
+
+  cr> SET GLOBAL TRANSIENT indices.store.throttle.max_bytes_per_sec = '5mb';
+  SET OK (... sec)
+
 
 Importing Data Using COPY FROM
 ------------------------------