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EPICS Fall Collaboration Meeting: Directory Service Development and Implementation Overview

This document outlines the key motivations and objectives for developing a generic Directory Service for EPICS. It emphasizes the need for a user-friendly system that allows clients to query channel data without prior knowledge of names. The service is designed to use standard protocols and provide RESTful web services, ensuring efficient performance. With an initial performance test showcasing retrieval times and a robust architecture relying on MySQL and LDAP for data management, the project is on track for version 1 release. Collaboration acknowledgments highlight contributions from various experts in the field.

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EPICS Fall Collaboration Meeting: Directory Service Development and Implementation Overview

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  1. ChannelFinderDirectory Service Ralph Lange EPICS Fall Collaboration Meeting, October 2010 BNL

  2. Motivation and Objectives • A flat name space restricts seriously: • Clients need to know all channel names beforehand • Portable generic clients must be simple • Apps need full configuration or framework supplied service • Develop a Directory Service • Generic • No dependency on installation and local conventions • Simple and fast (enough) • Use standards wherever possible • Provides “query-by-functionality”

  3. Directory Data • Set of Channels (unique names) • Each Channel has an arbitrary number ofProperties (name/value pairs) andTags (names) • Each Channel, Property, or Tag has an Owner (group) to allow basic access control • All names and values are strings

  4. Typical Middle-Tier Design • REST style web service • URI specifies the data element to operate on • HTTP method specifies the operation • Payload (XML, JSON) contains object representation • Application Server • RDB • Contains directory data • Use LDAP to query user-group relations

  5. Implementation REST Glassfish V3 MySQL LDAP Mercurial SourceForge Java EE 5 Netbeans 6.8 JDBC PyUnit XML JAX-RS Jersey JNDI Hudson JSON Maven 2 JAXB

  6. Directory Data Sources • IRMIS or other RDB systems Geographical, hierarchical, engineering, physics data • DB file parser (PV names, attributes) Requires a good naming convention • Control room applications ”Joe’s favorite channels”

  7. Targeted Applications • Waterfall Plots • Scripts • Generic applications • Table-style panels • Archive clients

  8. First Performance Estimates • Test database contains 150k channels, with 7 properties each • Performance of getting channels with properties by property wildcard match: 1st call subsequent calls 1 ch (500B data) 0.47s 0.009s 2k ch (700kB data) 0.6s 0.13s 4k ch (1.5MB data) 1.4s 0.9s (regular desktop machine, no optimization whatsoever)

  9. Status • Stabilizing, releasing v1 • Performance test suite in preparation • First generic applications developed • Acknowledgements / related work: • Gabriele Carcassi (App/Build Servers, IRMIS) • Don Dohan (IRMIS) • KunalShroff (Client Library and Applications) • Supported by Helmholtz-Zentrum Berlin / BESSY II

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