Release Notes for mongosync 1.21

New Features

• Adds the lag object to the /progress API response. The lag object reports synchronization lag as overallLagSeconds, crudLagSeconds, and ddlLagSeconds. The lagTimeSeconds field is deprecated in favor of lag.overallLagSeconds. See progress for more details.

Fixed Issues

• Fixes an issue where create, read, update, and delete (CRUD) events applied during Change Event Application (CEA) were sometimes double-counted in metrics and trace-level log messages.

• Fixes an issue where the embedded verifier could get stuck, causing some collections to never enter the initial hashing phase and preventing commit.

• Fixes an issue where mongosync incorrectly calculated remaining oplog time for sharded clusters, which resulted in an incorrect estimatedOplogTimeRemaining field or spurious warning messages in the /progress response.

• Fixes an issue where calling /resume very quickly after mongosync starts could cause mongosync to crash. Calling /resume before mongosync reaches the PAUSED state now returns an error.

Other Changes

• canCommit is false when mongosync or the embedded verifier reports more than 30 seconds of lag. Calling /commit when canCommit is false returns an error. See commit and progress for more details.

• Updates the behavior of estimatedTotalBytes and estimatedCopiedBytes in the /progress API response. If estimatedCopiedBytes exceeds estimatedTotalBytes during collection copy, mongosync raises estimatedTotalBytes to equal estimatedCopiedBytes. After collection copy, both values are equal. See progress for more details.

• When resuming a migration, mongosync now verifies that the --cluster0 and --cluster1 connection strings have not changed since the migration started. This check compares hostnames and ports to prevent potential data loss from accidentally swapping source and destination clusters.

Live Upgrades

Live upgrades to mongosync 1.21 are not supported.