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Tdengine biweekly selection of community issues | phase III
2022-07-06 08:46:00 【Tdengine】
Hi, Hello everyone , To prevent too many common problems from bothering users , Easy for users to learn 、 Absorb experience , We will select the common problems encountered by users in the community recently 、 Summary , Share with you in the form of a column . This is the third issue of this column , The content shared is as follows :
Content preview
- Why do I write data in batches , Timestamp use NOW Function splicing will result in data loss ?
- How to smoothly expand the capacity of a cluster ?
- After cluster expansion ,DNode Status as Offline How to investigate ?
- How to smoothly shrink a cluster ?
- Novice benefits : Quick start TDengine modeling .
1. Why do I write data in batches , Timestamp use NOW Function splicing will result in data loss ?
To answer this question, we first need to emphasize a concept ,TDengine As a Time series database (Time-Series Database), The first timestamp field acts as a primary key , Construction of memory index 、 The storage of disk data is closely related to it , There must be no duplicate timestamp .
NOW function ( as well as NOW keyword ) Return the current time of the client . When performing batch writes , If the values given by the timestamp in the first column are NOW, It is indistinguishable under the time level of milliseconds by default in the database , Repeated timestamps written later will be lost or updated , The specific logic for handling repeated timestamps is provided in TDengine China Construction Library (Database) At the time of the Update Parameter determination .
2. How to smoothly expand the capacity of a cluster ?
To expand the cluster, you need to add nodes manually . The specific operation steps are as follows :
- After the first node is successfully deployed , Install nodes to be added in sequence TDengine Server program , edit /etc/hosts, Add the domain name resolution of all nodes in the cluster ( If deployed DNS server, There is no need to edit ).
- The configuration file of the first node taos.cfg Copy to the node to be added , Will be one of the fqdn The parameter is changed to the node itself fqdn (hostname).
- Start the node to be added taosd service , Then enter taos The command line executes the following statement to add the node to be added into the cluster :CREATE DNode ‘Node2:6030’ .
- perform SHOW DNodes Check whether the status of the data node is Ready. by Ready On behalf of successful cluster expansion .
3. After cluster expansion ,DNode Status as Offline How to investigate ?
After the new node joins the cluster normally , The data node list will show that the node is in Ready state . If the node status is Offline, Check according to the following contents :
- View the node taosd Started or not 、 Whether the firewall is closed ;
- Confirm whether the data folder of the node to be added is empty ;
- Check all nodes /etc/hosts Whether the domain name resolution is complete 、 It works ( All nodes need to be resolved , Include arbitrator);
- The node firstEP、fqdn Whether the parameters are configured correctly .
4. How to smoothly shrink a cluster ?
Cluster capacity reduction is achieved through DROP DNode Delete nodes to achieve , Stop specifying directly DNode Of taosd The process will only let this node Offline, But it cannot complete the effect of volume reduction . The specific operation steps are as follows :
- Get into taos Command line , perform SHOW DNodes Check the status of the node to be deleted , if ready Then proceed to the next step ;
- Delete the specified node from the current cluster DROP DNode ‘Node2:6030’ perhaps DROP DNode <DNodeId>.
- perform SHOW DNodes View the cluster node information , Finally, confirm that the information of the node to be deleted has disappeared from the list .
Be careful : Before deleting nodes , The cluster will DNode Data is migrated to other nodes , The completion speed depends on the bandwidth of the network 、 On disk IO, Never stop the node to be deleted before it is completed taosd service .
5. Novice benefits : Quick start TDengine modeling .
In the process of community support , You can find many novice partners deploying TDengine I don't know how to further experience , Our suggestion is to run the sentences in the official website documents , But there are many documents , In order to facilitate community partners to get started quickly , We condense the example model of the official website document 、 I summed it up , Let users know as soon as possible TDengine Modeling methods :[ Introduction to modeling ]
complimentary close
Thank you for reading the selected questions in this issue , I hope the above is helpful to you . You are using TDengine This kind of TIme-Series Database In the process of , If you encounter a difficult problem or have a problem with TDengine There are suggestions for improvement , Welcome to the GitHub Let's talk about Issue , The more detailed the content, the better ~ Last , Thank you for using TDengine!
Want to know more TDengine Database Specific details of , Welcome to GitHub View the relevant source code on .
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