I'm trying to get real-time updates from MongoDB. I used the changes stream API (from here ). This is my code:
collection.watch().forEach(do_somthing);
But it just throws this error:
The $changeStream stage is only supported on replica sets
What is the meaning of replica sets
? How can I manage to fix this problem?
This is the first time I'm using MongoDB...
Thanks.
A replica set is a group of MongoDB processes that maintain the data set. Replica Sets replicate data by creating a special collection called the oplog which records all modifications to the data.
Change streams work by reading the oplog, so they require that your deployment are configured as a replica set.
See https://docs.mongodb.com/manual/tutorial/deploy-replica-set/ for a guide on deployment a replica set.
对于简单的本地测试,您可以像这样运行mongodb
mongod --dbpath=d:\data --oplogSize 50 --replSet rs0
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