What methods are used to coordinate data between two databases during migration?

When migrating data between two databases, the following methods are usually used for data reconciliation:

• Checksum comparison: calculating hashes for records or tables in both databases and comparing them to identify differences.

• Key-based synchronization: comparing records by unique keys (e.g., ID) and identifying missing or modified records.

• Using timestamps: if records contain a last modified date field, you can compare and update only the changed data.

• Two-way sync: if both databases can change, conflict resolution and data merging algorithms are applied.

• Change Data Capture (CDC): tracking changes in the source database and applying them to the target.

• Migration and ETL tools: using specialized tools that support data verification and reconciliation.

Example in Go for key-based data comparison:

// Assume there are two maps with data from different databases
sourceData := map[int]string{1: "A", 2: "B", 3: "C"}
destData := map[int]string{1: "A", 2: "X"}

for id, val := range sourceData {
    if destVal, ok := destData[id]; !ok {
        fmt.Printf("Record with ID %d is missing in the target database\n", id)
    } else if destVal != val {
        fmt.Printf("Record with ID %d differs: source='%s', dest='%s'\n", id, val, destVal)
    }
}

Thus, for data reconciliation, it is important to define unique keys, use checksums or timestamps, and apply appropriate comparison and update algorithms.