SSIS – An In-memory Pipeline
SSIS is an in-memory pipeline, so ensure that all transformations occur in memory.
The purpose of having Integration Services within SQL Server features is to provide a flexible, robust pipeline that can efficiently perform row-by-row calculations and parse data all in memory.
There are times where using Transact-SQL will be faster than processing the data in SSIS. As a general rule, any and all set-based operations will perform faster in Transact-SQL because the problem can be transformed into a relational (domain and tuple) algebra formulation that SQL Server is optimized to resolve. Set-based operations are far more efficient than row-by-row OLE DB calls.