![]() Operations in the MongoDB oplog are idempotent, so no matter how many times the operations are applied, they result in the same end state.Īs the MongoDB connector processes changes, it periodically records the position in the oplog where the event originated. When all the data is copied, the connector then starts streaming changes from the position it read earlier from the oplog. And, when the connector sees a replica set for the first time, it looks at the oplog to get the last recorded transaction and then performs a snapshot of the primary’s databases and collections. Just like MongoDB secondaries, however, the connector always reads the oplog of the replica set’s primary. ![]() The MongoDB connector uses this same replication mechanism, though it does not actually become a member of the replica set. This new server becomes a secondary (and able to handle queries) when it catches up to the tail of the primary’s oplog. ![]() When a new server is added to a replica set, that server first performs an snapshot of all of the databases and collections on the primary, and then reads the primary’s oplog to apply all changes that might have been made since it began the snapshot. MongoDB replication works by having the primary record the changes in its oplog (or operation log), and then each of the secondaries reads the primary’s oplog and applies in order all of the operations to their own documents. MongoDB connector captures the changes in a replica set or sharded cluster.Ī MongoDB replica set consists of a set of servers that all have copies of the same data, and replication ensures that all changes made by clients to documents on the replica set’s primary are correctly applied to the other replica set’s servers, called secondaries. MongoDB’s replication mechanism provides redundancy and high availability, and is the preferred way to run MongoDB in production.
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