Why is garbage collection log Metaspace value different from provided flag?

I am running a server app on Java 8 with the below flags:

-XX:GCLogFileSize=2097152 -XX:InitialBootClassLoaderMetaspaceSize=33554432 -XX:InitialHeapSize=1610612736 -XX:MaxHeapSize=1610612736 -XX:MaxMetaspaceSize=1073741824 -XX:MetaspaceSize=536870912 -XX:NumberOfGCLogFiles=5 -XX:+PrintGC -XX:+PrintGCApplicationConcurrentTime -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseGCLogFileRotation -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC

The metaspace start value is 512m and max value is 1gb.

In the GC logs I see different metaspace values than the above flag values. My log sample is below:

{Heap before GC invocations=1 (full 0):

 PSYoungGen      total 458752K, used 393216K [0x00000000e0000000, 0x0000000100000000, 0x0000000100000000)

  eden space 393216K, 100% used [0x00000000e0000000,0x00000000f8000000,0x00000000f8000000)

  from space 65536K, 0% used [0x00000000fc000000,0x00000000fc000000,0x0000000100000000)

  to   space 65536K, 0% used [0x00000000f8000000,0x00000000f8000000,0x00000000fc000000)

 ParOldGen       total 1048576K, used 0K [0x00000000a0000000, 0x00000000e0000000, 0x00000000e0000000)

  object space 1048576K, 0% used [0x00000000a0000000,0x00000000a00003a0,0x00000000e0000000)

 Metaspace       used 26975K, capacity 54120K, committed 54400K, reserved 1114112K

  class space    used 3346K, capacity 4426K, committed 4480K, reserved 1048576K

2016-12-21T16:41:10.569+0300: 1.423: [GC (GCLocker Initiated GC) [PSYoungGen: 393216K->29645K(458752K)] 393216K->29734K(1507328K), 0.0241803 secs] [Times: user=0.11 sys=0.00, real=0.02 secs] 

Heap after GC invocations=1 (full 0):

 PSYoungGen      total 458752K, used 29645K [0x00000000e0000000, 0x0000000100000000, 0x0000000100000000)

  eden space 393216K, 0% used [0x00000000e0000000,0x00000000e0000000,0x00000000f8000000)

  from space 65536K, 45% used [0x00000000f8000000,0x00000000f9cf3460,0x00000000fc000000)

  to   space 65536K, 0% used [0x00000000fc000000,0x00000000fc000000,0x0000000100000000)

 ParOldGen       total 1048576K, used 88K [0x00000000a0000000, 0x00000000e0000000, 0x00000000e0000000)

  object space 1048576K, 0% used [0x00000000a0000000,0x00000000a00163b0,0x00000000e0000000)

 Metaspace       used 26975K, capacity 54120K, committed 54400K, reserved 1114112K

  class space    used 3346K, capacity 4426K, committed 4480K, reserved 1048576K

}

So my question is: why don't I see the 512m and 1gb values for metaspace in the GC logs? Are the log values not directly related to flags?

edited Jan 2 at 10:29

DaveyDaveDave

3,81783758

asked Dec 21 '16 at 14:14

oguz karakus

48129

1

I generally recommend developers to remove all options they don’t understand. The JVM has reasonable defaults and it makes no sense to assume to know a better value than the JVM, without even understanding the actual meaning of the option.

– Holger
Dec 21 '16 at 17:05

The problem is, if i don't set the metaspace flags, server goes for many full gc in the startup. And i believe it is because metaspace becomes full, since it is something like 21mb as default for 64bit server. When i set the flag, full gc does not happen. My problem is solved. But i still want to understand the log and flag inconsistency.

– oguz karakus
Dec 22 '16 at 7:15

1

The -XX:MetaspaceSize doesn’t specify an initial size, but the threshold at which a gc should be triggered. So as long as the actual metaspace size is smaller than that, it won’t trigger a gc. But this threshold isn’t constant. During the runtime, the JVM may choose new values based on the actual usage. But anyway, why is the startup time of a server so important? Wouldn’t it make more sense to tune the parameters for the long time performance?

– Holger
Dec 22 '16 at 8:53

You are right about server start up time, it isn't that important, i was just tuning and wanted to get rid of full gc s at the start up and got curious at that point. Your last comment explains my misunderstanding of the flag, thank you for that. I can accept it if you can add it as answer.

– oguz karakus
Dec 22 '16 at 9:33

add a comment |

I am running a server app on Java 8 with the below flags:

-XX:GCLogFileSize=2097152 -XX:InitialBootClassLoaderMetaspaceSize=33554432 -XX:InitialHeapSize=1610612736 -XX:MaxHeapSize=1610612736 -XX:MaxMetaspaceSize=1073741824 -XX:MetaspaceSize=536870912 -XX:NumberOfGCLogFiles=5 -XX:+PrintGC -XX:+PrintGCApplicationConcurrentTime -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseGCLogFileRotation -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC

The metaspace start value is 512m and max value is 1gb.

In the GC logs I see different metaspace values than the above flag values. My log sample is below:

{Heap before GC invocations=1 (full 0):

 PSYoungGen      total 458752K, used 393216K [0x00000000e0000000, 0x0000000100000000, 0x0000000100000000)

  eden space 393216K, 100% used [0x00000000e0000000,0x00000000f8000000,0x00000000f8000000)

  from space 65536K, 0% used [0x00000000fc000000,0x00000000fc000000,0x0000000100000000)

  to   space 65536K, 0% used [0x00000000f8000000,0x00000000f8000000,0x00000000fc000000)

 ParOldGen       total 1048576K, used 0K [0x00000000a0000000, 0x00000000e0000000, 0x00000000e0000000)

  object space 1048576K, 0% used [0x00000000a0000000,0x00000000a00003a0,0x00000000e0000000)

 Metaspace       used 26975K, capacity 54120K, committed 54400K, reserved 1114112K

  class space    used 3346K, capacity 4426K, committed 4480K, reserved 1048576K

2016-12-21T16:41:10.569+0300: 1.423: [GC (GCLocker Initiated GC) [PSYoungGen: 393216K->29645K(458752K)] 393216K->29734K(1507328K), 0.0241803 secs] [Times: user=0.11 sys=0.00, real=0.02 secs] 

Heap after GC invocations=1 (full 0):

 PSYoungGen      total 458752K, used 29645K [0x00000000e0000000, 0x0000000100000000, 0x0000000100000000)

  eden space 393216K, 0% used [0x00000000e0000000,0x00000000e0000000,0x00000000f8000000)

  from space 65536K, 45% used [0x00000000f8000000,0x00000000f9cf3460,0x00000000fc000000)

  to   space 65536K, 0% used [0x00000000fc000000,0x00000000fc000000,0x0000000100000000)

 ParOldGen       total 1048576K, used 88K [0x00000000a0000000, 0x00000000e0000000, 0x00000000e0000000)

  object space 1048576K, 0% used [0x00000000a0000000,0x00000000a00163b0,0x00000000e0000000)

 Metaspace       used 26975K, capacity 54120K, committed 54400K, reserved 1114112K

  class space    used 3346K, capacity 4426K, committed 4480K, reserved 1048576K

}

So my question is: why don't I see the 512m and 1gb values for metaspace in the GC logs? Are the log values not directly related to flags?

edited Jan 2 at 10:29

DaveyDaveDave

3,81783758

asked Dec 21 '16 at 14:14

oguz karakus

48129

1

I generally recommend developers to remove all options they don’t understand. The JVM has reasonable defaults and it makes no sense to assume to know a better value than the JVM, without even understanding the actual meaning of the option.

– Holger
Dec 21 '16 at 17:05

The problem is, if i don't set the metaspace flags, server goes for many full gc in the startup. And i believe it is because metaspace becomes full, since it is something like 21mb as default for 64bit server. When i set the flag, full gc does not happen. My problem is solved. But i still want to understand the log and flag inconsistency.

– oguz karakus
Dec 22 '16 at 7:15

1

The -XX:MetaspaceSize doesn’t specify an initial size, but the threshold at which a gc should be triggered. So as long as the actual metaspace size is smaller than that, it won’t trigger a gc. But this threshold isn’t constant. During the runtime, the JVM may choose new values based on the actual usage. But anyway, why is the startup time of a server so important? Wouldn’t it make more sense to tune the parameters for the long time performance?

– Holger
Dec 22 '16 at 8:53

You are right about server start up time, it isn't that important, i was just tuning and wanted to get rid of full gc s at the start up and got curious at that point. Your last comment explains my misunderstanding of the flag, thank you for that. I can accept it if you can add it as answer.

– oguz karakus
Dec 22 '16 at 9:33

add a comment |

I am running a server app on Java 8 with the below flags:

-XX:GCLogFileSize=2097152 -XX:InitialBootClassLoaderMetaspaceSize=33554432 -XX:InitialHeapSize=1610612736 -XX:MaxHeapSize=1610612736 -XX:MaxMetaspaceSize=1073741824 -XX:MetaspaceSize=536870912 -XX:NumberOfGCLogFiles=5 -XX:+PrintGC -XX:+PrintGCApplicationConcurrentTime -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseGCLogFileRotation -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC

The metaspace start value is 512m and max value is 1gb.

In the GC logs I see different metaspace values than the above flag values. My log sample is below:

{Heap before GC invocations=1 (full 0):

 PSYoungGen      total 458752K, used 393216K [0x00000000e0000000, 0x0000000100000000, 0x0000000100000000)

  eden space 393216K, 100% used [0x00000000e0000000,0x00000000f8000000,0x00000000f8000000)

  from space 65536K, 0% used [0x00000000fc000000,0x00000000fc000000,0x0000000100000000)

  to   space 65536K, 0% used [0x00000000f8000000,0x00000000f8000000,0x00000000fc000000)

 ParOldGen       total 1048576K, used 0K [0x00000000a0000000, 0x00000000e0000000, 0x00000000e0000000)

  object space 1048576K, 0% used [0x00000000a0000000,0x00000000a00003a0,0x00000000e0000000)

 Metaspace       used 26975K, capacity 54120K, committed 54400K, reserved 1114112K

  class space    used 3346K, capacity 4426K, committed 4480K, reserved 1048576K

2016-12-21T16:41:10.569+0300: 1.423: [GC (GCLocker Initiated GC) [PSYoungGen: 393216K->29645K(458752K)] 393216K->29734K(1507328K), 0.0241803 secs] [Times: user=0.11 sys=0.00, real=0.02 secs] 

Heap after GC invocations=1 (full 0):

 PSYoungGen      total 458752K, used 29645K [0x00000000e0000000, 0x0000000100000000, 0x0000000100000000)

  eden space 393216K, 0% used [0x00000000e0000000,0x00000000e0000000,0x00000000f8000000)

  from space 65536K, 45% used [0x00000000f8000000,0x00000000f9cf3460,0x00000000fc000000)

  to   space 65536K, 0% used [0x00000000fc000000,0x00000000fc000000,0x0000000100000000)

 ParOldGen       total 1048576K, used 88K [0x00000000a0000000, 0x00000000e0000000, 0x00000000e0000000)

  object space 1048576K, 0% used [0x00000000a0000000,0x00000000a00163b0,0x00000000e0000000)

 Metaspace       used 26975K, capacity 54120K, committed 54400K, reserved 1114112K

  class space    used 3346K, capacity 4426K, committed 4480K, reserved 1048576K

}

So my question is: why don't I see the 512m and 1gb values for metaspace in the GC logs? Are the log values not directly related to flags?

edited Jan 2 at 10:29

DaveyDaveDave

3,81783758

asked Dec 21 '16 at 14:14

oguz karakus

48129

I am running a server app on Java 8 with the below flags:

-XX:GCLogFileSize=2097152 -XX:InitialBootClassLoaderMetaspaceSize=33554432 -XX:InitialHeapSize=1610612736 -XX:MaxHeapSize=1610612736 -XX:MaxMetaspaceSize=1073741824 -XX:MetaspaceSize=536870912 -XX:NumberOfGCLogFiles=5 -XX:+PrintGC -XX:+PrintGCApplicationConcurrentTime -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseGCLogFileRotation -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC

The metaspace start value is 512m and max value is 1gb.

In the GC logs I see different metaspace values than the above flag values. My log sample is below:

{Heap before GC invocations=1 (full 0):

 PSYoungGen      total 458752K, used 393216K [0x00000000e0000000, 0x0000000100000000, 0x0000000100000000)

  eden space 393216K, 100% used [0x00000000e0000000,0x00000000f8000000,0x00000000f8000000)

  from space 65536K, 0% used [0x00000000fc000000,0x00000000fc000000,0x0000000100000000)

  to   space 65536K, 0% used [0x00000000f8000000,0x00000000f8000000,0x00000000fc000000)

 ParOldGen       total 1048576K, used 0K [0x00000000a0000000, 0x00000000e0000000, 0x00000000e0000000)

  object space 1048576K, 0% used [0x00000000a0000000,0x00000000a00003a0,0x00000000e0000000)

 Metaspace       used 26975K, capacity 54120K, committed 54400K, reserved 1114112K

  class space    used 3346K, capacity 4426K, committed 4480K, reserved 1048576K

2016-12-21T16:41:10.569+0300: 1.423: [GC (GCLocker Initiated GC) [PSYoungGen: 393216K->29645K(458752K)] 393216K->29734K(1507328K), 0.0241803 secs] [Times: user=0.11 sys=0.00, real=0.02 secs] 

Heap after GC invocations=1 (full 0):

 PSYoungGen      total 458752K, used 29645K [0x00000000e0000000, 0x0000000100000000, 0x0000000100000000)

  eden space 393216K, 0% used [0x00000000e0000000,0x00000000e0000000,0x00000000f8000000)

  from space 65536K, 45% used [0x00000000f8000000,0x00000000f9cf3460,0x00000000fc000000)

  to   space 65536K, 0% used [0x00000000fc000000,0x00000000fc000000,0x0000000100000000)

 ParOldGen       total 1048576K, used 88K [0x00000000a0000000, 0x00000000e0000000, 0x00000000e0000000)

  object space 1048576K, 0% used [0x00000000a0000000,0x00000000a00163b0,0x00000000e0000000)

 Metaspace       used 26975K, capacity 54120K, committed 54400K, reserved 1114112K

  class space    used 3346K, capacity 4426K, committed 4480K, reserved 1048576K

}

So my question is: why don't I see the 512m and 1gb values for metaspace in the GC logs? Are the log values not directly related to flags?

java garbage-collection java-8 metaspace

edited Jan 2 at 10:29

DaveyDaveDave

3,81783758

asked Dec 21 '16 at 14:14

oguz karakus

48129

edited Jan 2 at 10:29

DaveyDaveDave

3,81783758

asked Dec 21 '16 at 14:14

oguz karakus

48129

edited Jan 2 at 10:29

DaveyDaveDave

3,81783758

edited Jan 2 at 10:29

DaveyDaveDave

3,81783758

edited Jan 2 at 10:29

DaveyDaveDave

3,81783758

asked Dec 21 '16 at 14:14

oguz karakus

48129

asked Dec 21 '16 at 14:14

oguz karakus

48129

asked Dec 21 '16 at 14:14

oguz karakus

48129

1

I generally recommend developers to remove all options they don’t understand. The JVM has reasonable defaults and it makes no sense to assume to know a better value than the JVM, without even understanding the actual meaning of the option.

– Holger
Dec 21 '16 at 17:05

The problem is, if i don't set the metaspace flags, server goes for many full gc in the startup. And i believe it is because metaspace becomes full, since it is something like 21mb as default for 64bit server. When i set the flag, full gc does not happen. My problem is solved. But i still want to understand the log and flag inconsistency.

– oguz karakus
Dec 22 '16 at 7:15

1

The -XX:MetaspaceSize doesn’t specify an initial size, but the threshold at which a gc should be triggered. So as long as the actual metaspace size is smaller than that, it won’t trigger a gc. But this threshold isn’t constant. During the runtime, the JVM may choose new values based on the actual usage. But anyway, why is the startup time of a server so important? Wouldn’t it make more sense to tune the parameters for the long time performance?

– Holger
Dec 22 '16 at 8:53

You are right about server start up time, it isn't that important, i was just tuning and wanted to get rid of full gc s at the start up and got curious at that point. Your last comment explains my misunderstanding of the flag, thank you for that. I can accept it if you can add it as answer.

– oguz karakus
Dec 22 '16 at 9:33

add a comment |

1

I generally recommend developers to remove all options they don’t understand. The JVM has reasonable defaults and it makes no sense to assume to know a better value than the JVM, without even understanding the actual meaning of the option.

– Holger
Dec 21 '16 at 17:05

The problem is, if i don't set the metaspace flags, server goes for many full gc in the startup. And i believe it is because metaspace becomes full, since it is something like 21mb as default for 64bit server. When i set the flag, full gc does not happen. My problem is solved. But i still want to understand the log and flag inconsistency.

– oguz karakus
Dec 22 '16 at 7:15

1

The -XX:MetaspaceSize doesn’t specify an initial size, but the threshold at which a gc should be triggered. So as long as the actual metaspace size is smaller than that, it won’t trigger a gc. But this threshold isn’t constant. During the runtime, the JVM may choose new values based on the actual usage. But anyway, why is the startup time of a server so important? Wouldn’t it make more sense to tune the parameters for the long time performance?

– Holger
Dec 22 '16 at 8:53

You are right about server start up time, it isn't that important, i was just tuning and wanted to get rid of full gc s at the start up and got curious at that point. Your last comment explains my misunderstanding of the flag, thank you for that. I can accept it if you can add it as answer.

– oguz karakus
Dec 22 '16 at 9:33

I generally recommend developers to remove all options they don’t understand. The JVM has reasonable defaults and it makes no sense to assume to know a better value than the JVM, without even understanding the actual meaning of the option.

– Holger
Dec 21 '16 at 17:05

The problem is, if i don't set the metaspace flags, server goes for many full gc in the startup. And i believe it is because metaspace becomes full, since it is something like 21mb as default for 64bit server. When i set the flag, full gc does not happen. My problem is solved. But i still want to understand the log and flag inconsistency.

– oguz karakus
Dec 22 '16 at 7:15

The -XX:MetaspaceSize doesn’t specify an initial size, but the threshold at which a gc should be triggered. So as long as the actual metaspace size is smaller than that, it won’t trigger a gc. But this threshold isn’t constant. During the runtime, the JVM may choose new values based on the actual usage. But anyway, why is the startup time of a server so important? Wouldn’t it make more sense to tune the parameters for the long time performance?

– Holger
Dec 22 '16 at 8:53

You are right about server start up time, it isn't that important, i was just tuning and wanted to get rid of full gc s at the start up and got curious at that point. Your last comment explains my misunderstanding of the flag, thank you for that. I can accept it if you can add it as answer.

– oguz karakus
Dec 22 '16 at 9:33

add a comment |

1 Answer
1

active

oldest

votes

As explained in “Advanced Garbage Collection Options”:

-XX:MetaspaceSize=size

Sets the size of the allocated class metadata space that will trigger a garbage collection the first time it is exceeded. This threshold for a garbage collection is increased or decreased depending on the amount of metadata used. The default size depends on the platform.

In other words, it doesn’t specify an initial size, but a first time gc threshold, so it matches your observed behavior of not having a full gc while the actual metaspace size is smaller than the specified size.

Once the threshold has been exceeded the first time, the JVM may choose a new threshold, based on the actual usage.

answered Dec 22 '16 at 10:01

Holger

170k23241459

add a comment |

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As explained in “Advanced Garbage Collection Options”:

-XX:MetaspaceSize=size

Sets the size of the allocated class metadata space that will trigger a garbage collection the first time it is exceeded. This threshold for a garbage collection is increased or decreased depending on the amount of metadata used. The default size depends on the platform.

Once the threshold has been exceeded the first time, the JVM may choose a new threshold, based on the actual usage.

answered Dec 22 '16 at 10:01

Holger

170k23241459

add a comment |

As explained in “Advanced Garbage Collection Options”:

-XX:MetaspaceSize=size

Sets the size of the allocated class metadata space that will trigger a garbage collection the first time it is exceeded. This threshold for a garbage collection is increased or decreased depending on the amount of metadata used. The default size depends on the platform.

Once the threshold has been exceeded the first time, the JVM may choose a new threshold, based on the actual usage.

answered Dec 22 '16 at 10:01

Holger

170k23241459

add a comment |

As explained in “Advanced Garbage Collection Options”:

-XX:MetaspaceSize=size

Sets the size of the allocated class metadata space that will trigger a garbage collection the first time it is exceeded. This threshold for a garbage collection is increased or decreased depending on the amount of metadata used. The default size depends on the platform.

Once the threshold has been exceeded the first time, the JVM may choose a new threshold, based on the actual usage.

answered Dec 22 '16 at 10:01

Holger

170k23241459

As explained in “Advanced Garbage Collection Options”:

-XX:MetaspaceSize=size

Sets the size of the allocated class metadata space that will trigger a garbage collection the first time it is exceeded. This threshold for a garbage collection is increased or decreased depending on the amount of metadata used. The default size depends on the platform.

Once the threshold has been exceeded the first time, the JVM may choose a new threshold, based on the actual usage.

answered Dec 22 '16 at 10:01

Holger

170k23241459

answered Dec 22 '16 at 10:01

Holger

170k23241459

answered Dec 22 '16 at 10:01

Holger

170k23241459

answered Dec 22 '16 at 10:01

Holger

170k23241459

add a comment |

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