[ozone] branch HDDS-3630 updated: HDDS-6790: Add document for Merge RocksDB in datanode feature. (#3451)

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The following commit(s) were added to refs/heads/HDDS-3630 by this push:
     new a6b5174fbb HDDS-6790: Add document for Merge RocksDB in datanode feature. (#3451)
a6b5174fbb is described below

commit a6b5174fbbc9282a59b2765433666d4c13399f2e
Author: Sammi Chen <sa...@apache.org>
AuthorDate: Thu May 26 10:38:25 2022 +0800

    HDDS-6790: Add document for Merge RocksDB in datanode feature. (#3451)
---
 .../docs/content/design/dn-merge-rocksdb.md        | 29 +++++++++
 .../docs/content/feature/dn-merge-rocksdb.md       | 70 ++++++++++++++++++++++
 2 files changed, 99 insertions(+)

diff --git a/hadoop-hdds/docs/content/design/dn-merge-rocksdb.md b/hadoop-hdds/docs/content/design/dn-merge-rocksdb.md
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+---
+title: Merge Container RocksDB in DN 
+summary: Use one RocksDB to hold all container metadata on a DN data volume
+date: 2022-05-24
+jira: HDDS-3630
+status: implemented
+
+---
+<!--
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License. See accompanying LICENSE file.
+-->
+
+# Abstract
+
+ Use one single RocksDB to hold all container metadata on a DN data volume, replacing the current one RocksDB for each container mode. 
+  
+# Link
+
+https://issues.apache.org/jira/secure/attachment/13044057/Merge%20rocksdb%20in%20datanode%20V5.pdf
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diff --git a/hadoop-hdds/docs/content/feature/dn-merge-rocksdb.md b/hadoop-hdds/docs/content/feature/dn-merge-rocksdb.md
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+++ b/hadoop-hdds/docs/content/feature/dn-merge-rocksdb.md
@@ -0,0 +1,70 @@
+---
+title: "Merge Container RocksDB in DN"
+weight: 2
+menu:
+   main:
+      parent: Features
+summary: Introduction to Ozone Datanode Container Schema V3
+---
+<!---
+  Licensed to the Apache Software Foundation (ASF) under one or more
+  contributor license agreements.  See the NOTICE file distributed with
+  this work for additional information regarding copyright ownership.
+  The ASF licenses this file to You under the Apache License, Version 2.0
+  (the "License"); you may not use this file except in compliance with
+  the License.  You may obtain a copy of the License at
+
+      http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+-->
+
+In Ozone, user data are separated into blocks and stored in HDDS Containers. Containers are the fundamental replication unit of Ozone/HDDS. Each Container has its metadata and data. Data are saved as files on disk. Metadata is saved in RocksDB.
+
+Currently there will be one RocksDB for each Container on datanode. With user data continously grow, there will be hundreds of thousands of RocksDB instances on one datanode. It's a big challenge to manage this amount of RocksDB instances in one JVM. 
+
+Unlike the current approach, this "Merge Container RocksDB in DN" feature will use only one RocksDB for each data volume, holding all metadata of Containers in this RocksDB. 
+  
+## Configuration
+
+This is mainly a DN feature, which doesn't require much configuration.
+
+Here is a configuration which disable this feature if the current one RocksDB for each container mode is more preferred. Please be noted that once the feature is enabled, it's strongly suggested not to disable it in later. 
+  
+```XML
+<property>
+   <name>hdds.datanode.container.schema.v3.enabled</name>
+   <value>false</value>
+   <description>Disable or enable this feature.</description>
+</property>
+```
+ 
+Without any specific configuration, the single RocksDB will be created under the data volume configured in "hdds.datanode.dir". 
+
+For some advanced cluster admins who have the high performance requirement, he/she can leverage quick storages to save RocksDB. In this case, configure these two properties.  
+
+```XML
+<property>
+   <name>hdds.datanode.container.db.dir</name>
+   <value/>
+   <description>This setting is optional. Specify where the per-disk rocksdb instances will be stored.</description>
+</property>
+<property>
+   <name>hdds.datanode.failed.db.volumes.tolerated</name>
+   <value>-1</value>
+   <description>The number of db volumes that are allowed to fail before a datanode stops offering service.
+   Default -1 means unlimited, but we should have at least one good volume left.</description>
+</property>
+```
+
+### Backward compatibility 
+
+Existing containers each has one RocksDB for them will be still accessible after this feature is enabled. All container data will co-exist in an existing Ozone cluster.
+
+## References
+
+ * [Design doc]({{< ref "design/dn-merge-rocksdb.md">}})
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