From 1091643978 at qq.com  Wed Sep 25 10:36:32 2019
From: 1091643978 at qq.com (=?gb18030?B?wfWyqA==?=)
Date: Wed, 25 Sep 2019 18:36:32 +0800
Subject: [jmm-dev] official docs about metaspace
Message-ID: <tencent_2932209E5CBA5201C3F7B97C3980B146CB07@qq.com>

hi, 
where's the office documents about metaspace ?


openjdk website search "metaspace" got lots of messages, does anyone know the official docs about metaspace, or any docs about it?


thanks

From 1091643978 at qq.com  Wed Sep 25 10:47:56 2019
From: 1091643978 at qq.com (=?utf-8?B?5YiY5rOi?=)
Date: Wed, 25 Sep 2019 18:47:56 +0800
Subject: [jmm-dev] official docs about metaspace
Message-ID: <tencent_979BCA0A78F2E8A20534DE39F2EF00DC1A09@qq.com>

hi, 
where's the office documents about metaspace ?


I want to know what's metaspace? what's it stores? how it's working? where can I find docs about metaspace?


openjdk website search "metaspace" got lots of messages, does anyone know the official docs about metaspace, or any docs about it?
 
I search all the jdk 8 documentation: none of there files talk about metaspace
 
grep -rnw ./* -e "Metaspace" --col                                                               ? 18:43:54 
 
./technotes/tools/unix/jstat.html:210:<p><code dir="ltr">MC</code>: Metaspace capacity (kB).</p>
 
./technotes/tools/unix/jstat.html:235:<p><code dir="ltr">MC</code>: Metaspace capacity (kB).</p>
 
./technotes/tools/unix/jstat.html:281:<p><code dir="ltr">MC</code>: Metaspace capacity (kB).</p>
 
./technotes/tools/unix/jstat.html:282:<p><code dir="ltr">MU</code>: Metaspace utilization (kB).</p>
 
./technotes/tools/unix/jstat.html:306:<p>Metaspace size statistics.</p>
 
./technotes/tools/unix/jstat.html:309:<p><code dir="ltr">MC</code>: Metaspace capacity (kB).</p>
 
./technotes/tools/unix/jstat.html:324:<p><code dir="ltr">M</code>: Metaspace utilization as a percentage of the space's current capacity.</p>
 
./technotes/tools/windows/jstat.html:210:<p><code dir="ltr">MC</code>: Metaspace capacity (kB).</p>
 
./technotes/tools/windows/jstat.html:235:<p><code dir="ltr">MC</code>: Metaspace capacity (kB).</p>
 
./technotes/tools/windows/jstat.html:281:<p><code dir="ltr">MC</code>: Metaspace capacity (kB).</p>
 
./technotes/tools/windows/jstat.html:282:<p><code dir="ltr">MU</code>: Metaspace utilization (kB).</p>
 
./technotes/tools/windows/jstat.html:306:<p>Metaspace size statistics.</p>
 
./technotes/tools/windows/jstat.html:309:<p><code dir="ltr">MC</code>: Metaspace capacity (kB).</p>
 
./technotes/tools/windows/jstat.html:324:<p><code dir="ltr">M</code>: Metaspace utilization as a percentage of the space's current capacity.</p>
 
./technotes/guides/troubleshoot/memleaks002.html:98:<dt><span><a id="sthref42" name="sthref42"/>Exception in thread <span>thread_name</span>: java.lang.OutOfMemoryError: Metaspace</span> </dt>
 
./technotes/guides/troubleshoot/memleaks002.html:132:<p><b>Note:</b> There is more than one kind of class metadata - <code dir="ltr">klass</code> metadata and other metadata. Only <code dir="ltr">klass</code> metadata is stored in the space bounded by <code dir="ltr">CompressedClassSpaceSize</code>. The other metadata is stored in <code dir="ltr">Metaspace</code>.</p>
 
./technotes/guides/vm/gctuning/considerations.html:97:  Metaspace       used 2425K, capacity 4498K, committed 4864K, reserved 1056768K
 
./technotes/guides/vm/gctuning/considerations.html:100:<p>In the line beginning with <code dir="ltr">Metaspace</code>, the <code dir="ltr">used</code> value is the amount of space used for loaded classes. The <code dir="ltr">capacity</code> value is the space available for metadata in currently allocated chunks. The <code dir="ltr">committed</code> value is the amount of space available for chunks. The <code dir="ltr">reserved</code> value is the amount of space reserved (but not necessarily committed) for metadata. The line beginning with <code dir="ltr">class space</code> line contains the corresponding values for the metadata for compressed class pointers.</p>

From aph at redhat.com  Wed Sep 25 16:52:44 2019
From: aph at redhat.com (Andrew Haley)
Date: Wed, 25 Sep 2019 17:52:44 +0100
Subject: [jmm-dev] official docs about metaspace
In-Reply-To: <tencent_979BCA0A78F2E8A20534DE39F2EF00DC1A09@qq.com>
References: <tencent_979BCA0A78F2E8A20534DE39F2EF00DC1A09@qq.com>
Message-ID: <bd81cdc3-63a3-c11c-037f-cb0a76a1d22a@redhat.com>

On 9/25/19 11:47 AM, ?? wrote:
> 
> I want to know what's metaspace? what's it stores? how it's working? where can I find docs about metaspace?
> 
> openjdk website search "metaspace" got lots of messages, does anyone know the official docs about metaspace, or any docs about it?

Not really. It's an internal detail of the virtual machine.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671

From adinn at redhat.com  Thu Sep 26 08:58:24 2019
From: adinn at redhat.com (Andrew Dinn)
Date: Thu, 26 Sep 2019 09:58:24 +0100
Subject: [jmm-dev] official docs about metaspace
In-Reply-To: <bd81cdc3-63a3-c11c-037f-cb0a76a1d22a@redhat.com>
References: <tencent_979BCA0A78F2E8A20534DE39F2EF00DC1A09@qq.com>
 <bd81cdc3-63a3-c11c-037f-cb0a76a1d22a@redhat.com>
Message-ID: <a90f55e6-0e53-d1fd-3107-197d6f8d57b3@redhat.com>

On 25/09/2019 17:52, Andrew Haley wrote:
> On 9/25/19 11:47 AM, ?? wrote:
>>
>> I want to know what's metaspace? what's it stores? how it's working? where can I find docs about metaspace?
>>
>> openjdk website search "metaspace" got lots of messages, does anyone know the official docs about metaspace, or any docs about it?
> 
> Not really. It's an internal detail of the virtual machine.

Briefly, Metaspace is the area of memory where the JVM stores 
information that tracks the internal state of the loaded class base and 
related interpreter and JIT compiler information.

I am not aware of any official OpenJDK project documentation that 
explains what Metaspace is and how it is managed. I gave a talk at 
FOSDEM 2018 that gives some details of what information is stored in 
metaspace and how you can use tools like jcmd to measure the amount of 
storage used:

   https://www.youtube.com/watch?v=jsJtZdYhQuE

The talk is based on 4 articles that provide a more full explanation. 
PDFs of those articles are available from my github space:

   https://github.com/adinn/fosdem2018

regards,

Andrew Dinn
-----------
Senior Principal Software Engineer
Red Hat UK Ltd
Registered in England and Wales under Company Registration No. 03798903
Directors: Michael Cunningham, Michael ("Mike") O'Neill, Eric Shander