Replikationslags

Replikationslags, often translated as replication lag or replication delay, refers to a phenomenon in distributed database systems and other replicated data architectures where there is a time difference between when a change is made to a primary data source and when that change is fully reflected in its replicas. This delay can arise due to various factors, including network latency, the amount of data being transferred, the processing power of the replica servers, and the synchronization method employed.

In a master-replica (or primary-secondary) setup, the primary database receives all write operations. These operations are then propagated to one or more replica databases. Replication lag occurs if the replicas do not receive and apply these updates instantaneously. The degree of lag is a critical performance metric, as it directly impacts the consistency of the data across the distributed system. Applications that read from replicas might therefore encounter stale data if replication lag is significant.

Different replication strategies, such as synchronous, asynchronous, and semi-synchronous replication, have varying impacts on replication lag. Synchronous replication aims to minimize lag by ensuring an update is confirmed by all replicas before it is considered complete, but this can increase write latency. Asynchronous replication offers lower write latency but can lead to higher replication lag. Semi-synchronous replication strikes a balance between the two. Monitoring and managing replication lag is essential for maintaining data integrity and ensuring application performance in distributed environments.