diff --git a/src/main/assemblies/files/fess.in.bat b/src/main/assemblies/files/fess.in.bat
index 6766d593b..79f4c47ee 100644
--- a/src/main/assemblies/files/fess.in.bat
+++ b/src/main/assemblies/files/fess.in.bat
@@ -55,10 +55,9 @@ set JAVA_OPTS=%JAVA_OPTS% -Djava.net.preferIPv4Stack=true
 
 set JAVA_OPTS=%JAVA_OPTS% -Djna.nosys=true
 set JAVA_OPTS=%JAVA_OPTS% -Djdk.io.permissionsUseCanonicalPath=true
-set JAVA_OPTS=%JAVA_OPTS% -XX:+UseConcMarkSweepGC
 
-set JAVA_OPTS=%JAVA_OPTS% -XX:CMSInitiatingOccupancyFraction=75
-set JAVA_OPTS=%JAVA_OPTS% -XX:+UseCMSInitiatingOccupancyOnly
+set JAVA_OPTS=%JAVA_OPTS% -XX:+UseG1GC
+set JAVA_OPTS=%JAVA_OPTS% -XX:InitiatingHeapOccupancyPercent=75
 
 set JAVA_OPTS=%JAVA_OPTS% -Dio.netty.noUnsafe=true
 set JAVA_OPTS=%JAVA_OPTS% -Dio.netty.noKeySetOptimization=true
diff --git a/src/main/assemblies/files/fess.in.sh b/src/main/assemblies/files/fess.in.sh
index 40ec701d4..e69177e3b 100755
--- a/src/main/assemblies/files/fess.in.sh
+++ b/src/main/assemblies/files/fess.in.sh
@@ -47,10 +47,8 @@ fi
 JAVA_OPTS="$JAVA_OPTS -Djna.nosys=true"
 JAVA_OPTS="$JAVA_OPTS -Djdk.io.permissionsUseCanonicalPath=true"
 
-JAVA_OPTS="$JAVA_OPTS -XX:+UseConcMarkSweepGC"
-
-JAVA_OPTS="$JAVA_OPTS -XX:CMSInitiatingOccupancyFraction=75"
-JAVA_OPTS="$JAVA_OPTS -XX:+UseCMSInitiatingOccupancyOnly"
+JAVA_OPTS="$JAVA_OPTS -XX:+UseG1GC"
+JAVA_OPTS="$JAVA_OPTS -XX:InitiatingHeapOccupancyPercent=75"
 
 JAVA_OPTS="$JAVA_OPTS -Dio.netty.noUnsafe=true"
 JAVA_OPTS="$JAVA_OPTS -Dio.netty.noKeySetOptimization=true"
diff --git a/src/main/java/org/codelibs/fess/mylasta/direction/FessConfig.java b/src/main/java/org/codelibs/fess/mylasta/direction/FessConfig.java
index 2807dfdf8..e02f810e1 100644
--- a/src/main/java/org/codelibs/fess/mylasta/direction/FessConfig.java
+++ b/src/main/java/org/codelibs/fess/mylasta/direction/FessConfig.java
@@ -47,13 +47,12 @@ public interface FessConfig extends FessEnv, org.codelibs.fess.mylasta.direction
     -XX:MaxMetaspaceSize=128m
     -XX:CompressedClassSpaceSize=32m
     -XX:-UseGCOverheadLimit
-    -XX:+UseConcMarkSweepGC
-    -XX:CMSInitiatingOccupancyFraction=75
-    -XX:+UseCMSInitiatingOccupancyOnly
     -XX:+UseTLAB
     -XX:+DisableExplicitGC
     -XX:+HeapDumpOnOutOfMemoryError
     -XX:-OmitStackTraceInFastThrow
+    -XX:+UseG1GC
+    -XX:InitiatingHeapOccupancyPercent=75
     -Djcifs.smb.client.responseTimeout=30000
     -Djcifs.smb.client.soTimeout=35000
     -Djcifs.smb.client.connTimeout=60000
@@ -82,12 +81,11 @@ public interface FessConfig extends FessEnv, org.codelibs.fess.mylasta.direction
     -XX:MaxMetaspaceSize=128m
     -XX:CompressedClassSpaceSize=32m
     -XX:-UseGCOverheadLimit
-    -XX:+UseConcMarkSweepGC
-    -XX:CMSInitiatingOccupancyFraction=75
-    -XX:+UseCMSInitiatingOccupancyOnly
     -XX:+UseTLAB
     -XX:+DisableExplicitGC
     -XX:+HeapDumpOnOutOfMemoryError
+    -XX:+UseG1GC
+    -XX:InitiatingHeapOccupancyPercent=75
     -Dgroovy.use.classvalue=true
     -Dio.netty.noUnsafe=true
     -Dio.netty.noKeySetOptimization=true
@@ -107,13 +105,12 @@ public interface FessConfig extends FessEnv, org.codelibs.fess.mylasta.direction
     -XX:MaxMetaspaceSize=128m
     -XX:CompressedClassSpaceSize=32m
     -XX:-UseGCOverheadLimit
-    -XX:+UseConcMarkSweepGC
-    -XX:CMSInitiatingOccupancyFraction=75
-    -XX:+UseCMSInitiatingOccupancyOnly
     -XX:+UseTLAB
     -XX:+DisableExplicitGC
     -XX:+HeapDumpOnOutOfMemoryError
     -XX:-OmitStackTraceInFastThrow
+    -XX:+UseG1GC
+    -XX:InitiatingHeapOccupancyPercent=75
     -Djcifs.smb.client.responseTimeout=30000
     -Djcifs.smb.client.soTimeout=35000
     -Djcifs.smb.client.connTimeout=60000
@@ -1484,13 +1481,12 @@ public interface FessConfig extends FessEnv, org.codelibs.fess.mylasta.direction
     -XX:MaxMetaspaceSize=128m
     -XX:CompressedClassSpaceSize=32m
     -XX:-UseGCOverheadLimit
-    -XX:+UseConcMarkSweepGC
-    -XX:CMSInitiatingOccupancyFraction=75
-    -XX:+UseCMSInitiatingOccupancyOnly
     -XX:+UseTLAB
     -XX:+DisableExplicitGC
     -XX:+HeapDumpOnOutOfMemoryError
     -XX:-OmitStackTraceInFastThrow
+    -XX:+UseG1GC
+    -XX:InitiatingHeapOccupancyPercent=75
     -Djcifs.smb.client.responseTimeout=30000
     -Djcifs.smb.client.soTimeout=35000
     -Djcifs.smb.client.connTimeout=60000
@@ -1524,12 +1520,11 @@ public interface FessConfig extends FessEnv, org.codelibs.fess.mylasta.direction
     -XX:MaxMetaspaceSize=128m
     -XX:CompressedClassSpaceSize=32m
     -XX:-UseGCOverheadLimit
-    -XX:+UseConcMarkSweepGC
-    -XX:CMSInitiatingOccupancyFraction=75
-    -XX:+UseCMSInitiatingOccupancyOnly
     -XX:+UseTLAB
     -XX:+DisableExplicitGC
     -XX:+HeapDumpOnOutOfMemoryError
+    -XX:+UseG1GC
+    -XX:InitiatingHeapOccupancyPercent=75
     -Dgroovy.use.classvalue=true
     -Dio.netty.noUnsafe=true
     -Dio.netty.noKeySetOptimization=true
@@ -1553,13 +1548,12 @@ public interface FessConfig extends FessEnv, org.codelibs.fess.mylasta.direction
     -XX:MaxMetaspaceSize=128m
     -XX:CompressedClassSpaceSize=32m
     -XX:-UseGCOverheadLimit
-    -XX:+UseConcMarkSweepGC
-    -XX:CMSInitiatingOccupancyFraction=75
-    -XX:+UseCMSInitiatingOccupancyOnly
     -XX:+UseTLAB
     -XX:+DisableExplicitGC
     -XX:+HeapDumpOnOutOfMemoryError
     -XX:-OmitStackTraceInFastThrow
+    -XX:+UseG1GC
+    -XX:InitiatingHeapOccupancyPercent=75
     -Djcifs.smb.client.responseTimeout=30000
     -Djcifs.smb.client.soTimeout=35000
     -Djcifs.smb.client.connTimeout=60000
@@ -8310,13 +8304,13 @@ public interface FessConfig extends FessEnv, org.codelibs.fess.mylasta.direction
             defaultMap.put(FessConfig.APP_DIGEST_ALGORISM, "sha256");
             defaultMap
                     .put(FessConfig.JVM_CRAWLER_OPTIONS,
-                            "-Djava.awt.headless=true\n-Dfile.encoding=UTF-8\n-Djna.nosys=true\n-Djdk.io.permissionsUseCanonicalPath=true\n-Dhttp.maxConnections=20\n-server\n-Xmx512m\n-XX:MaxMetaspaceSize=128m\n-XX:CompressedClassSpaceSize=32m\n-XX:-UseGCOverheadLimit\n-XX:+UseConcMarkSweepGC\n-XX:CMSInitiatingOccupancyFraction=75\n-XX:+UseCMSInitiatingOccupancyOnly\n-XX:+UseTLAB\n-XX:+DisableExplicitGC\n-XX:+HeapDumpOnOutOfMemoryError\n-XX:-OmitStackTraceInFastThrow\n-Djcifs.smb.client.responseTimeout=30000\n-Djcifs.smb.client.soTimeout=35000\n-Djcifs.smb.client.connTimeout=60000\n-Djcifs.smb.client.sessionTimeout=60000\n-Djcifs.smb1.smb.client.connTimeout=60000\n-Djcifs.smb1.smb.client.soTimeout=35000\n-Djcifs.smb1.smb.client.responseTimeout=30000\n-Dgroovy.use.classvalue=true\n-Dio.netty.noUnsafe=true\n-Dio.netty.noKeySetOptimization=true\n-Dio.netty.recycler.maxCapacityPerThread=0\n-Dlog4j.shutdownHookEnabled=false\n-Dlog4j2.disable.jmx=true\n-Dlog4j.skipJansi=true\n-Dsun.java2d.cmm=sun.java2d.cmm.kcms.KcmsServiceProvider\n-Dorg.apache.pdfbox.rendering.UsePureJavaCMYKConversion=true\n");
+                            "-Djava.awt.headless=true\n-Dfile.encoding=UTF-8\n-Djna.nosys=true\n-Djdk.io.permissionsUseCanonicalPath=true\n-Dhttp.maxConnections=20\n-server\n-Xmx512m\n-XX:MaxMetaspaceSize=128m\n-XX:CompressedClassSpaceSize=32m\n-XX:-UseGCOverheadLimit\n-XX:+UseTLAB\n-XX:+DisableExplicitGC\n-XX:+HeapDumpOnOutOfMemoryError\n-XX:-OmitStackTraceInFastThrow\n-XX:+UseG1GC\n-XX:InitiatingHeapOccupancyPercent=75\n-Djcifs.smb.client.responseTimeout=30000\n-Djcifs.smb.client.soTimeout=35000\n-Djcifs.smb.client.connTimeout=60000\n-Djcifs.smb.client.sessionTimeout=60000\n-Djcifs.smb1.smb.client.connTimeout=60000\n-Djcifs.smb1.smb.client.soTimeout=35000\n-Djcifs.smb1.smb.client.responseTimeout=30000\n-Dgroovy.use.classvalue=true\n-Dio.netty.noUnsafe=true\n-Dio.netty.noKeySetOptimization=true\n-Dio.netty.recycler.maxCapacityPerThread=0\n-Dlog4j.shutdownHookEnabled=false\n-Dlog4j2.disable.jmx=true\n-Dlog4j.skipJansi=true\n-Dsun.java2d.cmm=sun.java2d.cmm.kcms.KcmsServiceProvider\n-Dorg.apache.pdfbox.rendering.UsePureJavaCMYKConversion=true\n");
             defaultMap
                     .put(FessConfig.JVM_SUGGEST_OPTIONS,
-                            "-Djava.awt.headless=true\n-Dfile.encoding=UTF-8\n-Djna.nosys=true\n-Djdk.io.permissionsUseCanonicalPath=true\n-server\n-Xmx256m\n-XX:MaxMetaspaceSize=128m\n-XX:CompressedClassSpaceSize=32m\n-XX:-UseGCOverheadLimit\n-XX:+UseConcMarkSweepGC\n-XX:CMSInitiatingOccupancyFraction=75\n-XX:+UseCMSInitiatingOccupancyOnly\n-XX:+UseTLAB\n-XX:+DisableExplicitGC\n-XX:+HeapDumpOnOutOfMemoryError\n-Dgroovy.use.classvalue=true\n-Dio.netty.noUnsafe=true\n-Dio.netty.noKeySetOptimization=true\n-Dio.netty.recycler.maxCapacityPerThread=0\n-Dlog4j.shutdownHookEnabled=false\n-Dlog4j2.disable.jmx=true\n-Dlog4j.skipJansi=true\n");
+                            "-Djava.awt.headless=true\n-Dfile.encoding=UTF-8\n-Djna.nosys=true\n-Djdk.io.permissionsUseCanonicalPath=true\n-server\n-Xmx256m\n-XX:MaxMetaspaceSize=128m\n-XX:CompressedClassSpaceSize=32m\n-XX:-UseGCOverheadLimit\n-XX:+UseTLAB\n-XX:+DisableExplicitGC\n-XX:+HeapDumpOnOutOfMemoryError\n-XX:+UseG1GC\n-XX:InitiatingHeapOccupancyPercent=75\n-Dgroovy.use.classvalue=true\n-Dio.netty.noUnsafe=true\n-Dio.netty.noKeySetOptimization=true\n-Dio.netty.recycler.maxCapacityPerThread=0\n-Dlog4j.shutdownHookEnabled=false\n-Dlog4j2.disable.jmx=true\n-Dlog4j.skipJansi=true\n");
             defaultMap
                     .put(FessConfig.JVM_THUMBNAIL_OPTIONS,
-                            "-Djava.awt.headless=true\n-Dfile.encoding=UTF-8\n-Djna.nosys=true\n-Djdk.io.permissionsUseCanonicalPath=true\n-server\n-Xmx128m\n-XX:MaxMetaspaceSize=128m\n-XX:CompressedClassSpaceSize=32m\n-XX:-UseGCOverheadLimit\n-XX:+UseConcMarkSweepGC\n-XX:CMSInitiatingOccupancyFraction=75\n-XX:+UseCMSInitiatingOccupancyOnly\n-XX:+UseTLAB\n-XX:+DisableExplicitGC\n-XX:+HeapDumpOnOutOfMemoryError\n-XX:-OmitStackTraceInFastThrow\n-Djcifs.smb.client.responseTimeout=30000\n-Djcifs.smb.client.soTimeout=35000\n-Djcifs.smb.client.connTimeout=60000\n-Djcifs.smb.client.sessionTimeout=60000\n-Djcifs.smb1.smb.client.connTimeout=60000\n-Djcifs.smb1.smb.client.soTimeout=35000\n-Djcifs.smb1.smb.client.responseTimeout=30000\n-Dgroovy.use.classvalue=true\n-Dio.netty.noUnsafe=true\n-Dio.netty.noKeySetOptimization=true\n-Dio.netty.recycler.maxCapacityPerThread=0\n-Dlog4j.shutdownHookEnabled=false\n-Dlog4j2.disable.jmx=true\n-Dlog4j.skipJansi=true\n-Dsun.java2d.cmm=sun.java2d.cmm.kcms.KcmsServiceProvider\n-Dorg.apache.pdfbox.rendering.UsePureJavaCMYKConversion=true\n");
+                            "-Djava.awt.headless=true\n-Dfile.encoding=UTF-8\n-Djna.nosys=true\n-Djdk.io.permissionsUseCanonicalPath=true\n-server\n-Xmx128m\n-XX:MaxMetaspaceSize=128m\n-XX:CompressedClassSpaceSize=32m\n-XX:-UseGCOverheadLimit\n-XX:+UseTLAB\n-XX:+DisableExplicitGC\n-XX:+HeapDumpOnOutOfMemoryError\n-XX:-OmitStackTraceInFastThrow\n-XX:+UseG1GC\n-XX:InitiatingHeapOccupancyPercent=75\n-Djcifs.smb.client.responseTimeout=30000\n-Djcifs.smb.client.soTimeout=35000\n-Djcifs.smb.client.connTimeout=60000\n-Djcifs.smb.client.sessionTimeout=60000\n-Djcifs.smb1.smb.client.connTimeout=60000\n-Djcifs.smb1.smb.client.soTimeout=35000\n-Djcifs.smb1.smb.client.responseTimeout=30000\n-Dgroovy.use.classvalue=true\n-Dio.netty.noUnsafe=true\n-Dio.netty.noKeySetOptimization=true\n-Dio.netty.recycler.maxCapacityPerThread=0\n-Dlog4j.shutdownHookEnabled=false\n-Dlog4j2.disable.jmx=true\n-Dlog4j.skipJansi=true\n-Dsun.java2d.cmm=sun.java2d.cmm.kcms.KcmsServiceProvider\n-Dorg.apache.pdfbox.rendering.UsePureJavaCMYKConversion=true\n");
             defaultMap.put(FessConfig.JOB_SYSTEM_JOB_IDS, "default_crawler");
             defaultMap.put(FessConfig.JOB_TEMPLATE_TITLE_WEB, "Web Crawler - {0}");
             defaultMap.put(FessConfig.JOB_TEMPLATE_TITLE_FILE, "File Crawler - {0}");
diff --git a/src/main/resources/fess_config.properties b/src/main/resources/fess_config.properties
index 5be14d77a..cb7a60281 100644
--- a/src/main/resources/fess_config.properties
+++ b/src/main/resources/fess_config.properties
@@ -28,13 +28,12 @@ jvm.crawler.options=\
 -XX:MaxMetaspaceSize=128m\n\
 -XX:CompressedClassSpaceSize=32m\n\
 -XX:-UseGCOverheadLimit\n\
--XX:+UseConcMarkSweepGC\n\
--XX:CMSInitiatingOccupancyFraction=75\n\
--XX:+UseCMSInitiatingOccupancyOnly\n\
 -XX:+UseTLAB\n\
 -XX:+DisableExplicitGC\n\
 -XX:+HeapDumpOnOutOfMemoryError\n\
 -XX:-OmitStackTraceInFastThrow\n\
+-XX:+UseG1GC\n\
+-XX:InitiatingHeapOccupancyPercent=75\n\
 -Djcifs.smb.client.responseTimeout=30000\n\
 -Djcifs.smb.client.soTimeout=35000\n\
 -Djcifs.smb.client.connTimeout=60000\n\
@@ -63,12 +62,11 @@ jvm.suggest.options=\
 -XX:MaxMetaspaceSize=128m\n\
 -XX:CompressedClassSpaceSize=32m\n\
 -XX:-UseGCOverheadLimit\n\
--XX:+UseConcMarkSweepGC\n\
--XX:CMSInitiatingOccupancyFraction=75\n\
--XX:+UseCMSInitiatingOccupancyOnly\n\
 -XX:+UseTLAB\n\
 -XX:+DisableExplicitGC\n\
 -XX:+HeapDumpOnOutOfMemoryError\n\
+-XX:+UseG1GC\n\
+-XX:InitiatingHeapOccupancyPercent=75\n\
 -Dgroovy.use.classvalue=true\n\
 -Dio.netty.noUnsafe=true\n\
 -Dio.netty.noKeySetOptimization=true\n\
@@ -88,13 +86,12 @@ jvm.thumbnail.options=\
 -XX:MaxMetaspaceSize=128m\n\
 -XX:CompressedClassSpaceSize=32m\n\
 -XX:-UseGCOverheadLimit\n\
--XX:+UseConcMarkSweepGC\n\
--XX:CMSInitiatingOccupancyFraction=75\n\
--XX:+UseCMSInitiatingOccupancyOnly\n\
 -XX:+UseTLAB\n\
 -XX:+DisableExplicitGC\n\
 -XX:+HeapDumpOnOutOfMemoryError\n\
 -XX:-OmitStackTraceInFastThrow\n\
+-XX:+UseG1GC\n\
+-XX:InitiatingHeapOccupancyPercent=75\n\
 -Djcifs.smb.client.responseTimeout=30000\n\
 -Djcifs.smb.client.soTimeout=35000\n\
 -Djcifs.smb.client.connTimeout=60000\n\