"David Stein, Principal AI Engineer at ServiceTitan, presented Moving Mountains: Migrating Legacy Code in Weeks instead of Years at the very first QCon AI New York 2025. Stein kicked off his presentation describing how large-scale migrations are synonymous to "moving mountains." Major architectural changes have historically required a time measured in quarters-of-a-year to years along with an inherent risk in rewriting tremendous amounts of code."
"He presented an internal case study related to ServiceTitan having migrated their legacy reporting datasets to their new metric platform based on DBT Labs MetricFlow. This included: a reliance on production SQL databases; hundreds of metrics calculated in a monolith application using object-relational mapping; and thousands of lines of C# and complex SQL code. The timeline was quarters-of-a-year to years."
"Stein introduced the term, "false summit," a concept related to hazards that may occur during a migration that may lead to failure. The hard parts of the migration may sometimes stall and those benefits are never realized. Developers are left to ask, " Wait, are we building the right thing?" The Principle of Acceleration, a concept involving techniques to boost performance by optimizing data flow."
Large-scale migrations commonly require quarters-to-years and carry high risk from rewriting large amounts of code. ServiceTitan migrated legacy reporting datasets onto a new metric platform built on DBT Labs MetricFlow. The legacy system relied on production SQL databases, hundreds of metrics computed in a monolith via object-relational mapping, and thousands of lines of C# plus complex SQL. Migrations can stall on hard problems, producing a "false summit" where expected benefits never materialize. The Principle of Acceleration emphasizes optimizing data flow and adding a pre-migration validation step with standardized tools. An Assembly Line Pattern applies a sequential, automated CI/CD-style process for decomposing, building, testing, and deploying migrations.
#legacy-migration #dbt-labs-metricflow #assembly-line-pattern #principle-of-acceleration #false-summit
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