Speaker
Description
The XRootD redirector plays a key Role in CMS Experiment's global data access infrastructure, determining where clients are sent to retrieve data across a heterogeneous, worldwide set of storage endpoints. The redirector has traditionally emphasised simplicity and performance; Its decisions tend to be opaque and based on limited inputs. This can lead to erroneous redirections, such as sending clients to distant sites even when nearby replicas are available. Operators also lack sufficient observability to understand and diagnose redirector behaviour.
We present a set of enhancements to improve both the transparency and the effectiveness of redirector decisions for CMS. First, we introduce a new framework for redirector performance metrics, tracing and decision-making metadata. This instrumentation provides operators and clients with clear insights into how and why a particular redirection was chosen. Further, we investigate mechanisms to increase the reliability of redirections. Having made redirector decisions more reliable and reduced the need for client retries, we establish a foundation for incorporating more intelligent redirection logic that is both configurable and potentially pluggable. Examples include implementing custom plugins that use GeoIP information and other metrics to guide clients toward topologically favourable data sources.
Together, these improvements represent an important step in enhancing the robustness of CMS data access and analysis, and we hope to address long-standing pain points experienced by CMS physicists.