Consensus method for a distributed database

1. A computer-implemented consensus method for obtaining a valid global state for a distributed database, wherein the distributed database comprises main nodes, each main node storing a complete dataset, and a plurality of subsets of nodes, each subset configured to store a part of the dataset, the method comprising:

a. receiving a request for providing the valid global state of the distributed database;

b. determining by each subset of nodes a first local state for each subset based on status information of nodes of the respective subset regarding the respective part of the dataset;

c. combining the first local state of all subsets to a first combined state;

d. determining a global state by the main nodes based on status information of the main nodes regarding the stored dataset;

e. verifying the first combined state by matching the first combined state with the global state generating a verification result;

and

f. outputting the first combined state as the valid global state for the distributed database depending on the previously generated verification result.

2. The computer-implemented method according to claim 1 , wherein the first local state for each subset is determined by:

randomly selecting a node from the respective subset of nodes;

receiving node-specific status information of the selected node by the remaining nodes of the subset;

verifying the node-specific status information of the selected node through matching the status information with respective status information of the remaining nodes and generating a verification result;

and

outputting the status information of the selected node as the first local state depending on the previously generated verification result.

3. The computer-implemented method according to claim 1 , wherein verifying the first combined state is performed by all main nodes or by one randomly selected main node.

4. The computer-implemented method according to claim 1 , further comprising:

providing a second local state for each subset of nodes, wherein the second local state is determined based on status information of a randomly selected node from a subset other than the node selected for determining the first local state;

determining a second combined state by combining the second local states of all subsets;

verifying the second combined state by matching the second combined state with the global state and/or with the first combined state and generating a verification result;

and

outputting the second combined state as the valid global state depending on the previously generated verification result.

5. The computer-implemented method according to claim 1 , wherein in case of a mismatch between the first combined state and the global state a new first combined state is determined and verified until consensus is reached.

6. The computer-implemented method according to claim 1 , wherein in case of a mismatch between the second combined state and the global state a new second combined state is determined and verified until consensus is reached.

7. The computer-implemented method according to claim 1 , wherein in case of a mismatch between the first combined state and the global state and/or between the second combined state and the global state different main nodes are selected to determine a new global state.

8. The computer-implemented method according to claim 1 , wherein in case of a mismatch between the first combined state and the global state and/or between the second combined state and the global state the subset according to the mismatch is identified and at least one transaction is rolled back for that subset.

9. The computer-implemented method according to claim 1 , wherein the distributed database is a blockchain.

10. A computer program product, comprising a computer readable hardware storage device having computer readable program code stored therein, said program code executable by a processor of a computer system to implement a method according to claim 1 when the computer program product is run on a computer.

11. A distributed database comprising main nodes, each main node storing a dataset, and a plurality of subsets of nodes, each subset storing a part of the dataset, configured to perform a consensus method according to claim 1 for obtaining a valid global state of the distributed database.