How does Resumable Initial Sync work?

I want to know how “Resumable Initial Sync” works.

Fault Tolerance
Starting in MongoDB 4.4, a secondary performing initial sync can attempt to resume the sync process if interrupted by a transient (i.e. temporary) network error, collection drop, or collection rename. The sync source must also run MongoDB 4.4 to support resumable initial sync. If the sync source runs MongoDB 4.2 or earlier, the secondary must restart the initial sync process as if it encountered a non-transient network error.
By default, the secondary tries to resume initial sync for 24 hours. MongoDB 4.4 adds the initialSyncTransientErrorRetryPeriodSeconds server parameter for controlling the amount of time the secondary attempts to resume initial sync. If the secondary cannot successfully resume the initial sync process during the configured time period, it selects a new healthy source from the replica set and restarts the initial synchronization process from the beginning.
The secondary attempts to restart the initial sync up to 10 times before returning a fatal error.

Is there a special log or data that stores the status?

How does this work successfully?

Hi @Kim_Hakseon
You can find some more technical details in the Data Cloning section of the Replication Internals documentation and should answer your question.


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Thank you :smiley: :smiley:

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Hi @Kim_Hakseon,

One of our Technical Services engineers (@Nuno_Costa) wrote an article with more details on the new Resumable Initial Sync in MongoDB 4.4.

There’s a new forum topic for any questions or discussions on this: Would you like to know more about the new MongoDB v4.4 "Resumable Initial Sync" feature?.


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