Question

A data engineer runs a Fabric pipeline whose single Copy activity loads data from an on-premises SQL Server (via an on-premises data gateway) into a lakehouse Delta table. The activity succeeds but takes far longer than expected. In the Copy activity's monitoring detail view, the engineer sees that 'Duration' is dominated by a large value under 'Time to first byte' and 'Queue' time, while 'Throughput' and 'Data read/written' rates are low. What is the MOST likely cause of the slow performance?

Accepted Answer

The source query and gateway are the bottleneck — the gateway machine is under-resourced or the source query is slow, delaying data before the copy engine can transfer it

Answer

The lakehouse Delta table needs OPTIMIZE and Z-ORDER to reduce the number of small files being written

Answer

The pipeline schedule is triggering during a capacity throttling window, so the activity is being smoothed

Answer

Incremental refresh is not enabled on the destination table, forcing a full reload each run