MongoDB is a cross-platform database program that leverages JSON-like documents with optional schemas. This document-focused, NoSQL database program supplies support for search, transactional, mobile, and analytical use cases. MongoDB can provide these functionalities while leveraging a comprehensive data model and a common query interface loved by developers.
With MongoDB, you can easily protect data integrity and ensure high availability to propel business growth. MongoDB also ensures that your mission-critical workloads meet the compliance and security standards before moving forward. MongoDB provides you the ability to run confidently in production with indexing, sharding, pre-built replication, performance tools, and much more.
How does Replication Function in MongoDB?
MongoDB Replica set is a primary purpose is to offer high availability and data redundancy. MongoDB can maintain the durability of user data by keeping various replicas or copies of that data on physically isolated servers. Creating redundant data to safeguard and streamline data durability and availability is the definition of replication.
If your data is stored in a single database, untoward incidents like server crashes and hardware failures can make accessing your data impossible. But owing to replication, your applications can stay online in the event of database server failure. At the same time, MongoDB Replication also provides backup and disaster recovery options. Replication in MongoDB can be attained using a replica set. Here, writer operations are sent to the primary server (node) which can then apply the operations across secondary servers, replicating the data.
In case the primary fails or goes down due to an error, one of the secondary servers can take over to become the new primary node through an election. If the primary server comes back online, it becomes a secondary node once it fully recovers and supports the newly elected primary node.
The replica sets, typically a three-member system, ensures enough redundency for the system to tackle a majority of systems failuires or network partitions. Plus, replica sets should always have an odd number of members since this aids in a smooth election process.
Flow Control and Replication Lag
Replication Lag is symbolic of the average time it takes to replicate a complete write operation from your Primary to the secondary one. A small delay period might be acceptable, but as replication lag grows, considerable problems might erupt such as increased cache pressure on the primary node.
Starting from MongoDB 4.2, administrators can control the rate at which the primary node executes its write operations. This helps ensure the majority committed-based lag is always less than the programmable maximum value, typically present in the parameter: “flowControlTargetLagSeconds’. MongoDB enables flow control by default for efficient operations.
As the MongoDB Replication Lag grows closer to the ‘flowControlTargetLagSeconds’, Write operations on the primary node must acquire tickets before supplying locks to the Write operations. The flow control mechanism helps control the number of tickets that get issues every second. This in turn ensures that the lag due to replication is kept under the target parameter.
Replication Lag might be caused due to the following reasons:
- Concurrency: Since long-running applications on the primary node can impede replications, you need to set up your Write Concern so that the Write Operations don’t turn back if the replications are unable to tackle the load.
- Network Latency: You should check your traceroute and ping to assess if the issue encountered is due to packet loss or a network routing issue.
- Appropriate Write Concern: If the primary node requires a large number of write operations, the secondary nodes might not be able to bear the changes on the MongoDB oplog.
- Disk Throughput: Sometimes a secondary server can’t keep up with the rate at which the data is flushed with respect to the primary node. This is a common occurrence for multi-tenant systems, specifically if the disk devices are accessed by the system over an IP network.
What are the Benefits of MongoDB Replication?
You can reap various benefits from MongoDB Replication such as increased data reliability and availability. MongoDB ensures this because it stores multiple live copies of your data. Replication can also come in handy for an event like a server crash or hardware failure. Therefore, instead of letting you suffer downtime or complete loss of your data, MongoDB Replication ensures that your data is safely protected across various servers. In case you work with distributed analytics teams, you can efficiently collaborate on Business Intelligence Projects by leveraging MongoDB Replication.
This blog discusses the important aspects of a MongoDB Replica set briefly. This includes the benefits of MongoDB Replication and its working. It also helps you understand Replication Lag and Flow Control in MongoDB.
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