# Finisky Garden

Easy doesn't enter into grown-up life.

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Change stream是什么？官方文档:

Change streams allow applications to access real-time data changes without the complexity and risk of tailing the oplog. Applications can use change streams to subscribe to all data changes on a single collection, a database, or an entire deployment, and immediately react to them. Because change streams use the aggregation framework, applications can also filter for specific changes or transform the notifications at will.

• TLS验证有些问题，通过修改源码解决了
• all同步模式下，只能通过oplog进行了全量复制，在用change stream进行增量复制时不停抛错，无法正常运行

By the official manual:

Change streams allow applications to access real-time data changes without the complexity and risk of tailing the oplog. Applications can use change streams to subscribe to all data changes on a single collection, a database, or an entire deployment, and immediately react to them. Because change streams use the aggregation framework, applications can also filter for specific changes or transform the notifications at will.

Here we leverage change stream to replicate data from one MongoDB to another in realtime.

There is some existing tools such as MongoShake do the same thing. However, MongoShake is a little bit complicated to use. We encoutered two issues:

• Modify the source code to use TLS authentication
• Cannot perform increment sync in all sync_mode

Since our goal is realtime replication, we choose a more straightforward and controllable way: MongoDB Ops Manager cluster restore and change stream to apply realtime changes.

MongoDB change stream is a nice feature. It allows applications to access real-time data changes without the complexity and risk of tailing the oplog.

Recently, when we use change stream to replicate data from one sharded cluster to another, it immediately made the cluster unstable (broke down several nodes and triggered the primary change). Then the read/write operations latency significantly increased.

《天道》，丁元英