 CMS data challenges. The nature of the problem.  What is GMA ?  And what is R-GMA ?  Performance test description  Performance test results  Conclusions

 As part of the preparations for data taking CMS is performing DATA CHALLENGES.  Large number of simulated events to optimise detectors and prepare software  Enormous processing requirements BUT each event is independent of all the others each event can be generated on a machine without any interaction with any other

Work split between farms. How to handle the book-keeping ? a data-base automatically updated Implemented via a job wrapper BOSS Output to and is intercepted and the information is recorded in a mySQL production database. Event generation and job accounting decoupled

Database Machine Submission Machine UI Worker Node (WN) WN

Database Machine Submission Machine UI

Producer Consumer Registry (Directory services) register producer locate producer address of producer data Ask for data

Developed for E(uropean) D(ata) G(rid) Extends the GMA in two important ways 1.Introduces a time stamp on the data. 2.A relational implementation 3.Hides the registry behind the API Can be used for information and monitoring Each V irtual O rganisation appears to have one RDBMS

The user interface to R-GMA is via SQL statements (not all SQL statements and structures are supported) Information is advertised via a table create Information is published via insert Information is read via select … from table The first read request registers the consumer as interested in this data. Relational queries are supported NOTE : sql is the interface – it should not be supposed an actual database lies behind it.

R-GMA can be dropped into the framework with very little disruption 1. Set up calls for mySQL are replaced by those for R-GMA producers 2. An archiver (joint consumer/producer) runs on a single machine which collects the data from all the running jobs and writes it to a local database (and possible republishes it). The data can then be queried either by direct mySQL calls or via R-GMA consumer (a distributed database has been created)

Database BOSS LAN Connection R-GMA WAN Connection

 The architecture of GMA clearly provides a putative solution to the wide area monitoring problem. BUT Does a specific implementation provide a practical solution Before entrusting CMS production to R-GMA, we must be confident that it will perform. What load will it fail at and why ?

35 chars.

Multi-threaded job each thread produces messages. Length 35 chars, suitable distribution. Threads starting time distribution can be altered. One machine delivers the R-GMA load of a farm. R-GMA servlet R-GMA consumer

One machine per grid cluster providing loads of greater than the cluster R-GMA consumer R-GMA servlet R-GMA servlet R-GMA servlet R-GMA servlet

R-GMA can survive loads of around 20% of the current CMS requirements and does provides a grid method for monitoring. An overload of a factor 2 jobs causes problems after about five minutes running. We believe these instabilities are soluble. When production starts in earnest we will compare reality with our model.