Francesc Daniel Munoz-Escoi

Besides cryptocurrencies, DLTs may be also exploited in enterprise systems operated by a consortium of organizations. Their interaction takes usually place on a permissioned blockchain network that holds a set of data to be queried frequently. In this scope, the main problem of DLTs is their unsuitability for a fast service of complex queries on those data. In order to solve this issue, many proposals dump the ledger contents onto databases that, because of their own goals and design, are already optimized for the execution of those queries. Unfortunately, many of those proposals assume that the data to be queried consist in only a block or (cryptocurrency‐related) transaction history. However, those organization consortiums commonly store other structured business‐related information in the DLT, and there is an evident lack of support for querying that other kind of structured data. To remedy those problems, DELTA synchronizes, with minimal overhead, the DLT state into a database, providing (1) a modular architecture with event‐based handling of DLT updates that supports different DLTs and databases, (2) a transparent management, since DLT end users do not need to learn or use any new API in order to handle that synchronization (i.e., those users still rely on the original interface provided by their chosen DLT), (3) the efficient execution of complex queries on those structured data. Thus, DELTA reduces query times up to five orders of magnitude, depending on the DLT and the database, compared to queries directed to the ledger nodes.

Besides cryptocurrencies, DLTs may be also exploited in enterprise systems operated by a consortium of organizations. Their interaction takes usually place on a permissioned blockchain network that holds a set of data to be queried frequently. In this scope, the main problem of DLTs is their unsuitability for a fast service of complex queries on those data. In order to solve this issue, many proposals dump the ledger contents onto databases that, because of their own goals and design, are already optimized for the execution of those queries. Unfortunately, many of those proposals assume that the data to be queried consist in only a block or (cryptocurrency-related) transaction history. However, those organization consortiums commonly store other structured business-related information in the DLT, and there is an evident lack of support for querying that other kind of structured data. To remedy those problems, DELTA synchronizes, with minimal overhead, the DLT state into a database, providing: (1) a modular architecture with event-based handling of DLT updates that supports different DLTs and databases, (2) a transparent management, since DLT end users do not need to learn or use any new API in order to handle that synchronization (i.e., those users still rely on the original interface provided by their chosen DLT), (3) the efficient execution of complex queries on those structured data. Thus, DELTA reduces query times up to five orders of magnitude, depending on the DLT and the database, compared to queries directed to the ledger nodes.

Many modern distributed services are deployed in dynamic systems. Cloud services are an example. They are expected to provide service to a potentially huge amount of users and may require a wide geographical deployment in multiple data centres. Their service processes vary in volume in accordance with workload variations, showing an adaptive behaviour in order to minimise economical costs. Dynamic distributed systems may be classifed considering two axes: (a) the number of processes that compose the system, and (b) the diameter of the networking graph that interconnects those processes. Other important features of dynamic systems can be derived from these two characteristics, e.g., their attainable synchrony. We analyse the level of synchrony that may be achieved in each dynamic system class and revise the existing techniques for transforming an initially asynchronous large dynamic system into another one with a higher synchrony level. With this, a larger set of problems may be handled in dynamic distributed systems. This facilitates the implementation and provision of additional services in those systems.