Separate "data sets" from the current database and some things live on for years

An application I helped with in 1999 loaded Corporate ledger data from 1989 through 1999 for a web based retrieval application function. Large amounts of ledger detail was stored in a SQL Server data warehouse. The data definition was flexible enough to support transition to a new ledger sources and integration of other ledger sources as the corporate world evolved. The size is just short of 2 TB.

The data structure and extract methodologies were well thought out, creating a single view of multiple ledgers with low level detail. This is unheard of in the world of ledger detail. As the company evolved/merged/reorganized more ledger data was summarized the history, and each new system lost it's historic detail. in 2011 the ledger feed was terminated with the thought the application would go away.

Years later this Ledger data warehouse is the sole historic repository of leger data still used in contract closeout and recon, Rate determination, and audit projects. The original Application containing the feature is long gone, but the Actuals data warehouse remains a standalone application no one can afford to delete, despite corporate pressure to eliminate old applications.

Lesson learned, transaction databases can age away, but their history may live on.