1. ATLAS Distributed Computing Tutorial Tags: What, Why, When, Where and How? Mike Kenyon University of Glasgow

2. Tags • What are tags? • Why have them? • When are they produced? • Where are they? • How can they be used?

3. What are Event Tags? • Event-level metadata: summary information about events, with a “pointer” to the corresponding AOD/ESD/RDO format • Useful for selecting events for physics analysis • Should be no bigger than 1KB per event (~ 1% AOD size)

4. Why have Event Tags? • To make Physicist’s life easier and analysis faster • Allows you to exclude uninteresting events from data sample used for analysis without searching through AOD/ESD files • Samples of specific interest to an analysis can be extracted into a smaller set of files for repeated running • Provides a global view of the data, useful for data mining • Not to do analysis on directly

5. Tag Use Cases • Some Physicist use cases: • Using official Tags with query in job options • Using local Tag “database” for preliminary analysis • Using global Tag database to look for events • Using global Tag database to build input list for Athena jobs

6. What do they look like? • The LCG POOL infrastructure is used to store Tags • Hence use of “collection” terminology • They exist in 2 forms: • ROOT files • Relational database (MySQL and Oracle) • Why keep 2 forms? • ROOT files useful for local work • DB useful for queries, global view of data • Tag content: collection information + event information

7. Tag Content • Collection Information • Collection ID, AOD/ESD/RDO references • Global Event Quantities • Event no., run no., no. of tracks, missing ET etc • Trigger Decisions • Electrons, Photons, Muons • Number, PT, h, f, etc • Jets, Taus • Number, PT, h, f, etc

8. When are Tags produced? • Written to ROOT files at Tier 0 during AOD production – “Explicit collections” • Data then imported into central relational database (Oracle at CERN) • Database replicated to Tier 1 and lower • Oracle where available; MySQL otherwise • Users can create their own tag files

10. Sample Queries • General Collection Information • How many events in collection A? • What are the names and types of Tag attributes? • What production task(s) produced these Tags? • Content Queries • Give me all events with at least 2 electrons and missing ET > 10 GeV which are ‘good for physics’ • Summary Queries • Give me the number of events for some content query • Give me sum of the luminosity for some content query

11. How can Tags be used? • Collection tools • Athena • Tag Navigator Tool (TNT)

12. Collection Tools • To use Tags in Athena, you need to know what the attributes are • POOL Collection tools can be used for this • Can copy collections, append collections, print list of files used, etc • Allows queries on the input collections • See Tutorial Exercises, part 1

13. Tags in Athena • Both ROOT and Relational Tags can be read directly from Athena • Need file catalogue to find the AOD files, and Athena version which matches that used by the Tags • One can also produce private ROOT Tags from AOD • Focus here is on reading, rather than building, Tags

14. Local Tag Files with Athena • jobOptions for event selection look like:

15. Remote Tag Database with Athena • Not many Tags available in central database yet • This constrains the exercises somewhat, but we can at least illustrate the principles • jobOptions must include lines like: EventSelector.InputCollections = ['rome_4312_merge_H12_140_gamgam_AOD_tags’] EventSelector.Connection = 'oracle://atlas_tags/atlas_tags_rome’ EventSelector.CollectionType = 'ExplicitRAL'

16. Tag Navigator Tool (TNT) • A utility which aims to allow ATLAS physicists to use the Tag database for analysis • Runs a query on the database and outputs a local ROOT collection • Divides this into a number of sub-collections • Submits user jobs to LCG, one per sub-collection • Output files can be registered as new DQ2 dataset

17. What’s there now? • There is still a lot of work to be done to get an efficient Tag system running • Currently running performance / scalability tests on central database • Need Tags to be produced and loaded into database as a matter of course • Tag database from Rome workshop is still there, now awaiting Tags from Streaming Tests

18. And finally… • Tags will become ever more useful as real data appears • Infrastructure is still being developed • Wednesday’s exercises aimed at familiarisation with ideas and methods