samperson1997 commented on a change in pull request #1384:
URL: https://github.com/apache/incubator-iotdb/pull/1384#discussion_r443362901
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File path: docs/SystemDesign/SchemaManager/SchemaManager.md
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@@ -175,6 +175,16 @@ The root node exists by default. Creating storage groups,
deleting storage group
* Deleting a storage group is similar to deleting a time series. That is, the
storage group or time series node is deleted in its parent node. The time
series node also needs to delete its alias in the parent node; if in the
deletion process, a node is found not to have any child node, needs to be
deleted recursively.
+## MTree checkpoint
+
+To speed up restarting of IoTDB, we set checkpoint for MTree. Every several
minutes, background thread checks the last modified time of MTree. If users
haven’t modified MTree for more than 1 hour (which means `mlog.txt` hasn’t been
updated for more than 1 hour), and `mlog.txt` has reached the threshold line
number of user configuration, MTree snapshot is created. In this way, we could
avoid reading mlog.txt and executing the commands line by line.
+
+The serialization of MTree is depth-first from children to parent. Information
of nodes are converted into String according to different node types, which is
convenient for deserialization.
+
+* Common MNode: 0,name,children size
Review comment:
Fixed
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