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

BUTeach 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 automaticallyupdated

Implemented via a job wrapper BOSSOutput to <stdout> and <stderr> is intercepted and the information is recorded in a mySQL production database.Event generation and job accounting decoupled

DatabaseMachine

SubmissionMachine

UI

WorkerNode (WN) WN

WN

WN

WNWN

WN

WN

WN

DatabaseMachine

SubmissionMachine

UI

Producer

Consumer

Registry (Directory services)

register producer

locate producer

address of producer

data

data

data

data

Ask fordata

data

data

data

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 Virtual Organisation 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 createInformation is published via insertInformation 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)

DatabaseBOSS

LAN Connection

R-GMAR-GMAR-GMAR-GMAR-GMAR-GMAR-GMAR-GMA

WAN Connection

The architecture of GMA clearly provides a putative solution to the wide area monitoring problem.

BUTDoes 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 ?

<Message length> 35 chars.

Multi-threaded jobeach 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-GMAconsumer

One machine per grid cluster providing loads of greater than the cluster

R-GMAconsumer

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.