1. A DAPT IST-2001-37126 JBora Reliable Group Communication Middleware Alberto Bartoli Etienne Antoniutti Di Muro Milan Prica Università degli Studi di Trieste, Italy

2. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) What is JBora? JBora is the user application interface towards a replication layer Built on top of Spread Group Communication tool JBora is a shared object amongst all application threads within the same VM Programmer Code Spread JBora JMiramare Group Communication Layer } Replication Algorithm } 2 / 16 JBora

3. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) What Can You Do With JBora ? Usual things… –Join a group –Multicast message and receive events –Leave a group Inter-thread communication (useful when interacting with external channel, e.g. HTTP) –localCall() and localRespond() novel primitives Share application level information, among replicas, i.e. load information, sensor data –WhiteBoard object shared among group members 3 / 16

4. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) JBora: Reliability Guarantees  Total Order + Uniform Delivery In Partitionable Systems Without Transitional Views Not going to discuss this in detail… 4 / 16

5. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) JBora: Group Communication Performance No Free Lunch –GC: powerful but costly –Likely to be a key bottleneck Objective –Can we shift the GC-induced bottleneck up to higher throughput values ? 5 / 16 YES! Use message packing!

6. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) Methodology: Message Packing (I) APPLICATION Replication middleware GC middleware operation multicast “Traditional” (“Standard”) use of Group Communication 6 / 16

7. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) Methodology: Message Packing (II) operation Message Packing (Friedman, Van Renesse 1996) buffered (fixed) packing interval 7 / 16 APPLICATION Replication middleware GC middleware

8. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) JBora Key Feature: Adaptive Message Packing Message buffer is transmitted when sending conditions have been satisfied: –packing interval has elapsed –packing degree has been reached –packing dimension has been reached Each parameter may be kept constant or varied at runtime 8 / 16

9. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) JBora Key Feature: Adaptive Message Packing We have seen that with suitable values we can have very good performance The problem is how to tune this once and for all ? Idea!: Enable the system to tune itself automatically and adaptively 9 / 16

10. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) What is a Policy? A policy is a pluggable module that enables to obtain adaptive behaviour Run-time access to performance related sensors Modifies packing parameters accordingly Throughput Latency CPU usage SENSORS PackingDegree PackingInterval ACTUATORS Packing Layer Replication Middleware GC Middleware POLICY 10 / 16

11. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) JBora Adaptive Message Packing Performance Throughput vs. clients test application - 3 replicas 10% 11 / 16

12. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) Policy Implementation Notes interface DynamicPacking { void applyPolicy(PackingConfiguration,int[][]); } PackingConfiguration : class that handles message packing parameters int[][]: table of sensor measurements, one row per sensor 12 / 16

13. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) Policy Examples Constant policy: “Dummy Policy”. Keeps message packing parameters constant, as defined at configuration time. Max Throughput policy: Accesses throughput sensor measurements, and adjusts message packing degree in order to increase message throughput. CPU policy: Accesses CPU sensor measurements, and adjusts message packing degree in order to decrease CPU usage 13 / 16

14. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) Open Issues Latency issues 14 / 16 Packing Degree = 1 Packing Degree = 10 replicated application w/o message packing Latency vs. clients test application - 3 replicas Tailoring policies to the application Developing new sensors: is it worthy ? +27% +40%

15. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) JBora Configuration JBora adaptability parameters –packing interval –packing degree –packing dimension –policy module class name Where to put the configuration file ? Who handles configuration parameters DOM ? 15 / 16

16. A DAPT 4th ADAPT Workshop, 11-12 December 2003, Bologna (Italy) Questions ? 16 / 16