MongoDB security improvement mainly relies on three aspects: authentication, authorization and encryption. 1. Enable the authentication mechanism, configure --auth at startup or set security.authorization:enabled, and create a user with a strong password to prohibit anonymous access. 2. Implement fine-grained authorization, assign minimum necessary permissions based on roles, avoid abuse of root roles, review permissions regularly, and create custom roles. 3. Enable encryption, encrypt communication using TLS/SSL, configure PEM certificates and CA files, and combine storage encryption and application-level encryption to protect data privacy. The production environment should use trusted certificates and update policies regularly to build a complete security line.

MongoDBAtlas' free hierarchy has many limitations in performance, availability, usage restrictions and storage, and is not suitable for production environments. First, the M0 cluster shared CPU resources it provides, with only 512MB of memory and up to 2GB of storage, making it difficult to support real-time performance or data growth; secondly, the lack of high-availability architectures such as multi-node replica sets and automatic failover, which may lead to service interruption during maintenance or failure; further, hourly read and write operations are limited, the number of connections and bandwidth are also limited, and the current limit can be triggered; finally, the backup function is limited, and the storage limit is easily exhausted due to indexing or file storage, so it is only suitable for demonstration or small personal projects.

The main difference between updateOne(), updateMany() and replaceOne() in MongoDB is the update scope and method. ① updateOne() only updates part of the fields of the first matching document, which is suitable for scenes where only one record is modified; ② updateMany() updates part of all matching documents, which is suitable for scenes where multiple records are updated in batches; ③ replaceOne() completely replaces the first matching document, which is suitable for scenes where the overall content of the document is required without retaining the original structure. The three are applicable to different data operation requirements and are selected according to the update range and operation granularity.

Use deleteOne() to delete a single document, which is suitable for deleting the first document that matches the criteria; use deleteMany() to delete all matching documents. When you need to remove a specific document, deleteOne() should be used, especially if you determine that there is only one match or you want to delete only one document. To delete multiple documents that meet the criteria, such as cleaning old logs, test data, etc., deleteMany() should be used. Both will permanently delete data (unless there is a backup) and may affect performance, so it should be operated during off-peak hours and ensure that the filtering conditions are accurate to avoid mis-deletion. Additionally, deleting documents does not immediately reduce disk file size, and the index still takes up space until compression.

TTLindexesautomaticallydeleteoutdateddataafterasettime.Theyworkondatefields,usingabackgroundprocesstoremoveexpireddocuments,idealforsessions,logs,andcaches.Tosetoneup,createanindexonatimestampfieldwithexpireAfterSeconds.Limitationsincludeimprecisedel

MongoDBhandlestimeseriesdataeffectivelythroughtimeseriescollectionsintroducedinversion5.0.1.Timeseriescollectionsgrouptimestampeddataintobucketsbasedontimeintervals,reducingindexsizeandimprovingqueryefficiency.2.Theyofferefficientcompressionbystoring

MongoDB's RBAC manages database access through role assignment permissions. Its core mechanism is to assign the role of a predefined set of permissions to the user, thereby determining the operations and scope it can perform. Roles are like positions, such as "read-only" or "administrator", built-in roles meet common needs, and custom roles can also be created. Permissions are composed of operations (such as insert, find) and resources (such as collections, databases), such as allowing queries to be executed on a specific collection. Commonly used built-in roles include read, readWrite, dbAdmin, userAdmin and clusterAdmin. When creating a user, you need to specify the role and its scope of action. For example, Jane can have read and write rights in the sales library, and inve

Migrating relational databases to MongoDB requires focusing on data model design, consistency control and performance optimization. First, convert the table structure into a nested or referenced document structure according to the query pattern, and use nesting to reduce association operations are preferred; second, appropriate redundant data is appropriate to improve query efficiency, and judge whether to use transaction or application layer compensation mechanisms based on business needs; finally, reasonably create indexes, plan sharding strategies, and select appropriate tools to migrate in stages to ensure data consistency and system stability.