Support for persistent global (non-partitioned) indexes on partitioned tables in Db2 Data Gate for Db2 for z/OS to Db2 LUW topologies

In Db2 Data Gate topologies that replicate data from Db2 for z/OS to Db2 for Linux, UNIX, and Windows (LUW), there is currently a functional limitation in which global (non-partitioned) indexes on partitioned tables are not supported, as documented by IBM. Because of this restriction, any custom index defined as non-partitioned is either not allowed or not preserved during Data Gate Load Operations, requiring customers to rely exclusively on partitioned indexes.

This limitation creates a significant challenge for specific yet highly realistic workloads in which global indexes are essential for effective query optimization and where partitioned index equivalents do not provide the same access path benefits. The issue becomes critical in scenarios involving relatively small tables that are frequently refreshed through LOAD REPLACE operations multiple times per day, while still supporting ongoing online DML activity. In the described use case, the Db2 advisor consistently indicated performance benefits from using global indexes; however, the corresponding partitioned index alternatives failed to produce effective access paths, resulting in table scans and excessive CPU consumption. In contrast, defining the same index as a global (non-partitioned) index immediately enabled index-based access, significantly reduced query cost, and allowed the target Db2 LUW system to sustain the required transaction volume.

We are requesting that IBM consider adding support for persistent global (non-partitioned) indexes on partitioned tables in Db2 Data Gate topologies between Db2 for z/OS and Db2 LUW. This support could be implemented as:

• An optional configuration, allowing customers to opt in;
• A documentation stating that such indexes may impact replication performance or to ensure customers understand the trade-offs

The intent is not to replace partitioned indexes by default, but to allow customers to make the choice when global indexes are demonstrably required for workload performance.