MetaParticles
The MetaParticles are always broadcasted to every bolt/instance of bolt within topology.
At this moment there are 2 types implemented: Timer MetaParticle and GracefulShutdown MetaParticle
###Timer MetaParticle Sometimes there is a need in a specific timer for data processing instead of using the only available real-time timer from Apache Storm. it could be needed for replaying the specific dataset processing, a special simulation, etc.
Timer MetaParticle is the particle that sets the timer spread out through the whole SensorStorm topology. It contains the timer which every bolt can use for every operation on data. For the details of implementation see Figure 1.
Figure1. Timer MetaParticle
Timer MetaParticle contains the timer which the TimerMetaParticleHandler uses in executing of every operation on coming data. By using TimeControllerInterface handler first registers the needed type of operation to use this exact timer in its execution, and after that these operations use the timer in question.
###GracefulShutdown MetaParticle From time to time it is required to stop the data processing by specific Storm topology (i.e., in case of starting new changed version of topology, upgrading the topology, complete stopping of topology which is not needed, etc.). The meaning of Graceful Shutdown MetaParticle is to be able to stop data processing gracefully, with the processing of all Particles which are already within the topology till the end. The bolts are shutting down one by one from the start of topology till the end. Every bolt is being shutting down only when it has processed all the available for it Particles, and pushed them to the next Bolt. Every instance of Bolt should be guaranteed to shut down after the processing, that is why the GracefulShutdown MetaParticle is broadcasted to every instance of any type of Bolt within the topology. The details of the current implementation of Graceful Shutdown MetaParticle are demonstrated at Fig. 2.
Figure1. Graceful Shutdown MetaParticle
At this moment this type of MetaParticle is in progress of implementation.