restvm.blogg.se - Lag vs dsync

LAG VS DSYNC FULL

Replication is also largely non-blocking on the replica side.This means that the master will continue to handle queries when one or more replicas perform the initial synchronization or a partial resynchronization. Redis replication is non-blocking on the master side.Since Redis 4.0, all the sub-replicas will receive exactly the same replication stream from the master. Aside from connecting a number of replicas to the same master, replicas can also be connected to other replicas in a cascading-like structure. Replicas are able to accept connections from other replicas.Redis uses asynchronous replication, with asynchronous replica-to-master acknowledges of the amount of data processed.The rest of this document mainly describes the basic characteristics of Redis basic replication.

You can check the Redis Sentinel or Redis Cluster documentation for more informationĪbout high availability and failover. However with WAIT the probability of losing a writeĪfter a failure event is greatly reduced to certain hard to trigger failure Writes can still be lost during a failover, depending on the exact configuration Turn a set of Redis instances into a CP system with strong consistency: acknowledged Specified number of acknowledged copies in the other Redis instances, it does not However WAIT is only able to ensure there are the Synchronous replication of certain data can be requested by the clients using This allows having optional synchronous replication. So the master does not wait every timeįor a command to be processed by the replicas, however it knows, if needed, what They received periodically with the master. However, Redis replicas asynchronously acknowledge the amount of data High performance, is the natural replication mode for the vast majority of Redis Redis uses by default asynchronous replication, which being low latency and This will involve a more complex process in which the master needs to create a snapshot of all its data, send it to the replica, and then continue sending the stream of commands as the dataset changes.

LAG VS DSYNC FULL

When a partial resynchronization is not possible, the replica will ask for a full resynchronization.

When the link between the master and the replica breaks, for network issues or because a timeout is sensed in the master or the replica, the replica reconnects and attempts to proceed with a partial resynchronization: it means that it will try to just obtain the part of the stream of commands it missed during the disconnection.

When a master and a replica instances are well-connected, the master keeps the replica updated by sending a stream of commands to the replica to replicate the effects on the dataset happening in the master side due to: client writes, keys expired or evicted, any other action changing the master dataset.

This system works using three main mechanisms: The replica will automatically reconnect to the master every time the link breaks, and will attempt to be an exact copy of it regardless of what happens to the master. It allows replica Redis instances to be exact copies of master instances. How Redis supports high availability and failover with replicationĪt the base of Redis replication (excluding the high availability features provided as an additional layer by Redis Cluster or Redis Sentinel) there is a leader follower (master-replica) replication that is simple to use and configure.