[GitHub] [ozone] guihecheng commented on a diff in pull request #3451: HDDS-6790: Add document for Merge RocksDB in datanode feature.

[GitBox <gi...@apache.org>]

guihecheng commented on code in PR #3451:
URL: https://github.com/apache/ozone/pull/3451#discussion_r880268871


##########
hadoop-hdds/docs/content/feature/dn-merge-rocksdb.md:
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@@ -0,0 +1,87 @@
+---
+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>

Review Comment:
   Seems to be a misformat.



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