
Why ETL and Change Data Capture Break at Mainframe Scale — and What Replaces Them
VirtualZ Computing Executive Chairman Marc Sokol and CTO Vince Re break down how a Fortune 500 retailer moved a 60-million-record VSAM file from z/OS to PostgreSQL in the cloud at a sustained 56,000 records per second — with no staging database, no change data capture, and zero lines of custom code. The same file on their previous solution ran for two days. VSAM (Virtual Storage Access Method) is the mainframe's core file structure, and getting it into a relational database has traditionally meant one of three things: hand-built ETL scripts that break whenever a copybook changes, a change data capture deployment that demands VSAM logging and RLS, or a staged gateway architecture that reads and writes the same data four times. Vince Re explains why all three break down at enterprise scale — including one customer who spent two years on a CDC approach and never got it working. In this episode of Skyward Data, the podcast from VirtualZ Computing: The real benchmark environment — a mid-sized z/OS system, 4K+ record sizes, a shared 10 Gb link, and GCP-hosted PostgreSQL, using no more than 3–5% of available bandwidth Why single-pass processing beats staged architectures that touch the data four times How COBOL copybook metadata drives field-level transformation declaratively — packed decimal, binary, floating point, and EBCDIC into relational columns with no code Why JDBC bulk operations, large batches, and deferred commits outperform per-record HTTP and web services approaches What VSAM logging actually costs in I/O, journal storage, batch window, and deadlock risk How the multiplexer processes thousands of files in parallel instead of serially Running PropelZ on z/OS, on Linux, or anywhere with a Java environment Licensing that is per platform — not per LPAR, not per MIPS, not by data volume PropelZ is VirtualZ Computing's no-code tool for extracting and transforming IBM Z mainframe data to any target. It's part of a four-product portfolio alongside Lozen (real-time read-write access to live mainframe data without moving it), FlowZ (mainframe files to cloud object storage), and Zaac (cloud and SAN presented as native z/OS disk and tape). Topics: VSAM to PostgreSQL migration, mainframe data migration, IBM Z, z/OS, change data capture alternatives, no-code ETL, COBOL copybook transformation, EBCDIC conversion, zIIP offload, VSAM to Db2, mainframe modernization, hybrid cloud data integration, AI data pipelines, Snowflake, Databricks. Listen to more Skyward Data episodes: https://virtualzcomputing.com/podcasts/














