Add -XX+AlwaysPreTouch JVM flag

Enables the touching of all memory pages used by the JVM heap spaces
during initialization of the HotSpot VM, which commits all memory pages
at initialization time. By default, pages are committed only as they are
needed.

Author: dakrone

distribution/src/main/resources/bin/elasticsearch.in.bat

@@ -85,6 +85,10 @@ REM JAVA_OPTS=%JAVA_OPTS% -XX:HeapDumpPath=$ES_HOME/logs/heapdump.hprof
 REM Disables explicit GC
 set JAVA_OPTS=%JAVA_OPTS% -XX:+DisableExplicitGC
 
+REM Enable pre-touching of memory pages used by the JVM during hotspot
+REM initialization
+set JAVA_OPTS=%JAVA_OPTS% -XX:+AlwaysPreTouch
+
 REM Ensure UTF-8 encoding by default (e.g. filenames)
 set JAVA_OPTS=%JAVA_OPTS% -Dfile.encoding=UTF-8
 

distribution/src/main/resources/bin/elasticsearch.in.sh

@@ -81,6 +81,10 @@ JAVA_OPTS="$JAVA_OPTS -XX:+HeapDumpOnOutOfMemoryError"
 # Disables explicit GC
 JAVA_OPTS="$JAVA_OPTS -XX:+DisableExplicitGC"
 
+# Enable pre-touching of memory pages used by the JVM during hotspot
+# initialization
+JAVA_OPTS="$JAVA_OPTS -XX:+AlwaysPreTouch"
+
 # Ensure UTF-8 encoding by default (e.g. filenames)
 JAVA_OPTS="$JAVA_OPTS -Dfile.encoding=UTF-8"
 

docs/reference/migration/migrate_5_0.asciidoc

@@ -808,6 +808,15 @@ changed to now route standard output to the journal and standard error
 to inherit this setting (these are the defaults for systemd). These
 settings can be modified by editing the elasticsearch.service file.
 
+==== Longer startup times
+
+In Elasticsearch 5.0.0 the `-XX:+AlwaysPreTouch` flag has been added to the JVM
+startup options. This option touches all memory pages used by the JVM heap
+during initialization of the HotSpot VM to reduce the chance of having to commit
+a memory page during GC time. This will increase the startup time of
+Elasticsearch as well as increasing the initial resident memory usage of the
+Java process.
+
 [[breaking_50_scripting]]
 === Scripting