Bulk Update (BU) Lock in SQL Server

 A Bulk Update Lock, or BU Lock, is a specialized table-level lock used by SQL Server during bulk loading operations such as BULK INSERT, bcp imports, OPENROWSET(BULK), and certain large-scale insert operations performed with TABLOCK. The primary objective of the BU Lock is to maximize bulk load throughput while reducing lock management overhead and enabling minimal logging when recovery model and table conditions permit. Unlike Exclusive Locks, BU Locks are designed specifically for bulk operations and have unique compatibility characteristics that can allow multiple bulk-loading sessions to coexist. During ETL and data warehouse loads involving millions of rows, BU Locks significantly improve performance by avoiding excessive row-level locking and reducing transaction log activity. They are commonly observed in staging tables, landing zones, and fact-table loading processes. Understanding BU Locks is important for designing high-performance ETL architectures, troubleshooting bulk load bottlenecks, and explaining how SQL Server balances concurrency and throughput during large-scale data ingestion.

BU Lock is a specialized table lock designed to maximize bulk load throughput.

A Bulk Update (BU) Lock is a special table-level lock used by SQL Server during bulk data load operations such as BULK INSERT, bcp, OPENROWSET(BULK...), and certain INSERT...SELECT WITH (TABLOCK) operations. The purpose of a BU lock is to improve bulk load performance while allowing multiple bulk loaders to work concurrently under specific conditions. It is less restrictive than an Exclusive (X) lock but more restrictive than a Shared (S) lock.