What are hashed shard keys versus ranged shard keys, and their respective use cases?

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.

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

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.

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

MongoDB's read preference determines how to route the application's read operations to the replica set members. All read operations are sent to the master node by default, but different read preferences can be configured according to requirements to optimize performance and data consistency. The main modes include primary (only read the master node, ensuring the latest data), primaryPreferred (priority master node, use secondary node when not available), secondary (secondary node only, suitable for offloading the primary node load), secondaryPreferred (priority secondary node, use primary node when there is no secondary), and nearest (select the node with the lowest network latency, regardless of primary or secondary). These patterns affect query routing methods, and are driven

MongoDBAtlas is more suitable for small teams or organizations lacking DBA resources because it provides fully automatic management, rapid deployment and built-in security; 2. Atlas is transparent and easy to budget in the early stage, but it may be higher than self-hosting after large usage. Although the infrastructure fee is low, it needs to be included in the labor and risk costs; 3. In terms of security and compliance, Atlas defaults to enterprise-level configuration and automatically updates, and self-hosting needs to be implemented manually and is prone to errors; 4. Select from hosting when it requires strong control, customization needs or data sovereignty restrictions, otherwise most teams should choose Atlas first to focus on product development rather than operation and maintenance. This choice is the most time-saving and reliable and supports flexible adjustments in the future.

MongoDBintroducedmulti-documenttransactionsinversion4.0,enablingatomicoperationsacrosscollectionsforstrongconsistency.Transactionsallowmultipleread/writeoperationstobegroupedasasingleunit,eitherallsucceedingorfailingtogether.Theyaresupportedinreplica