tencent cloud



Last updated: 2022-04-08 14:37:58

    How do I view instance details in MongoDB?

    You can click an instance ID in the instance list to enter the details page and view the details.

    How do I access a MongoDB instance?

    TencentDB for MongoDB can be connected by using a variety of programming languages, such as Shell, PHP, Node.js, Java, and Python.
    For more information, see Connection Sample.

    The time required for upgrading an instance depends on its used capacity. Primary-secondary switch will occur once during the upgrade, and the instance will be temporarily inaccessible for about ten seconds.

    How do I create an instance in MongoDB?

    On the purchase page, you can specify the specification and usage period and click Buy Now to create an instance.

    How do I find an instance with assigned projects in MongoDB?

    To find an instance with assigned projects, call the DescribeDBInstances API to query the list of instances.

    What is the number of connections in MongoDB? Can I increase the number?

    See Use Limits. The number of connections depends on instance specifications. You can increase the number by upgrading instance specifications.

    How do I view the slow logs of a TencentDB for MongoDB instance?

    You can log in to the console and select Database Management > Slow Query Management on the instance management page to query slow logs.

    How do I query the instance specifications supported by MongoDB?

    You can call the DescribeSpecInfo API to query the supported instance specifications.

    How do I choose between a replica set instance and sharded cluster instance?

    • A replica set instance consists of one primary node and one or more secondary nodes. You can select a replica set instance in the following business scenarios:

      • The data volume does not exceed the total instance capacity.
        You can check whether the capacity specification of the replica set instance selected during instance creation meets your requirements to select an appropriate instance.
      • The write traffic is low while the read traffic is high.
        You can scale out secondary nodes to solve the performance bottleneck of excessive read traffic. For detailed directions, see Adjusting Instance Specification.
      • There are a large number of database collections, but the document data volume in each collection is low.
      • In scenarios where multiple randomly combined fields are queried, if a sharded cluster instance is used and it is hard to select an appropriate shardkey index, we recommend you use a replica set instance.
    • Compared with a replica set instance, a sharded cluster instance breaks through the bottlenecks of data capacity and write traffic and has a complete horizontal scalability. Select a sharded cluster instance in the following scenarios:

      • The estimated data volume exceeds the capacity limit of a replica set instance.
        You can view the capacity limit of a replica set instance during instance creation to select an appropriate instance.
      • The write traffic exceeds the write traffic limit of a replica set instance.

    How do I set the priority for database read operations?

    If your business does not require a high data consistency, you can configure read/write separation to reduce the request pressure on the primary node and improve the read performance. By default, TencentDB for MongoDB reads the primary node first. If you want to specify access to secondary nodes, set the Read Preference parameter on the client to configure the read policy. The values of Read Preference are as detailed below:

    Value Description Default
    primary Reads the primary node only. Yes
    primaryPreferred Reads the primary node first. If it is not available, a secondary node will be read. No
    secondary Reads a secondary node only. If it is not available, an error will be reported. No
    secondaryPreferred Reads a secondary node first. If it is not available, the primary node will be read. No
    nearest Reads the nearest node with the lowest network latency. No

    To read a secondary node first, you can configure the URI as follows:


    How do I solve the problem of reduced write performance when the majority of nodes are written?

    For data writes, you can select different write concern policies based on your requirements for business data reliability. For more information, see Write Concern.

    Option Description Scenario
    {w: 0} No acknowledgment messages are required for data writes by the client The data integrity is not concerned.
    {w: 1} An acknowledgment message will be sent to the client after data is written to the primary node. This is the default write concern option. A balance between the performance and data reliability is required.
    {w: majority} An acknowledgment message will be sent to the client after data is written to the majority of nodes in the replica set. A high data integrity is required in order to avoid data rollbacks.

    If you requires a high data reliability, you can set the write concern option w to majority and use the {j: true} option to ensure that the acknowledgment message will be returned only after the journal log is persisted during data write. This can avoid data rollbacks but significantly decreases the write performance.

    How to optimize
    You can optimize the write performance by disabling the chain replication feature. If there are three nodes A, B, and C, among which node B syncs data from node A and node C syncs data from node B, then a chain sync structure (A > B > C) is formed as shown below:

    1. TencentDB for MongoDB multi-node replica set instances support chain replication. Run the following command to check whether the current replica set supports chain replication:

      1.    cmgo-xx:SECONDARY> rs.conf().settings.chainingAllowed  
      2.    true  
      3.    cmgo-xx:SECONDARY> 
    2. Check whether chain replication exists in the current replica set nodes. You can view the sync source of each node. If a sync source is a secondary node, there is chain replication in the replica set. Below is the sample code:

      1.    cmgo-xx:SECONDARY> rs.status().syncSourceHost  
      2.    xx.xx.xx.xx:7021  
      3.    cmgo-xx:SECONDARY> 
    3. Run the following command to disable chain replication:

      1.    cfg = rs.config()  
      2.    cfg.settings.chainingAllowed = false
      3.    rs.reconfig(cfg) 
    Contact Us

    Contact our sales team or business advisors to help your business.

    Technical Support

    Open a ticket if you're looking for further assistance. Our Ticket is 7x24 avaliable.

    7x24 Phone Support