SOLR-7319: Workaround for the "Four Month Bug" GC pause problem

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1669731 13f79535-47bb-0310-9956-ffa450edef68

solr/CHANGES.txt

@@ -91,6 +91,15 @@ Upgrading from Solr 5.0
   contain some LGPL-only code. Until that's resolved by Tika, you can download the
   .jar yourself and place it under contrib/extraction/lib.  
 
+* A twitter engineer discovered a JVM bug that causes GC pause problems.  The
+  workaround for those problems makes certain functionality impossible, such as
+  running the jstat program on your Solr instance.  That workaround has been
+  implemented in the bin/solr start scripts.  If you need the missing java
+  functionality, delete the "-XX:+PerfDisableSharedMem" parameter from
+  bin/solr.in.sh or bin/solr.in.cmd.
+
+  http://www.evanjones.ca/jvm-mmap-pause.html
+
 Detailed Change List
 ----------------------
 
@@ -341,6 +350,12 @@ Bug Fixes
 * SOLR-7309: Make bin/solr, bin/post work when Solr installation directory contains spaces
   (Ramkumar Aiyengar, Martijn Koster)
 
+* SOLR-7319: Workaround for the "Four Month Bug" GC pause problem discovered
+  by a twitter software engineer.  This causes GC pauses when JVM statistics
+  are left enabled and there is heavy MMAP write activity.
+  http://www.evanjones.ca/jvm-mmap-pause.html
+  (Shawn Heisey)
+
 Optimizations
 ----------------------
 

solr/bin/solr.in.cmd

@@ -40,6 +40,7 @@ set GC_TUNE=-XX:NewRatio=3 ^
  -XX:+UseCMSInitiatingOccupancyOnly ^
  -XX:CMSInitiatingOccupancyFraction=50 ^
  -XX:CMSMaxAbortablePrecleanTime=6000 ^
+ -XX:+PerfDisableSharedMem ^
  -XX:+CMSParallelRemarkEnabled ^
  -XX:+ParallelRefProcEnabled
 

solr/bin/solr.in.sh

@@ -37,6 +37,7 @@ GC_TUNE="-XX:NewRatio=3 \
 -XX:PretenureSizeThreshold=64m \
 -XX:+UseCMSInitiatingOccupancyOnly \
 -XX:CMSInitiatingOccupancyFraction=50 \
+-XX:+PerfDisableSharedMem \
 -XX:CMSMaxAbortablePrecleanTime=6000 \
 -XX:+CMSParallelRemarkEnabled \
 -XX:+ParallelRefProcEnabled"