Patent Publication Number: US-11030044-B2

Title: Dynamic blockchain data storage based on error correction code

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT Application No. PCT/CN2019/118180, filed on Nov. 13, 2019, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This specification relates to blockchain data storage based on error correction code. 
     BACKGROUND 
     Distributed ledger systems (DLSs), which can also be referred to as consensus networks, and/or blockchain networks, enable participating entities to securely and immutably store data. DLSs are commonly referred to as blockchain networks without referencing any particular user case. Examples of types of blockchain networks can include public blockchain networks, private blockchain networks, and consortium blockchain networks. A consortium blockchain network is provided for a select group of entities, which control the consensus process, and includes an access control layer. 
     Blockchain-based programs can be executed by a distributed computing platform. For example, the distributed computing platform can include a virtual machine that provides the runtime environment for executing smart contracts. A blockchain computing platform can be viewed as a transaction-based state machine. State data in the platform can be assembled to a global shared-state referred to as a world state. The world state includes a mapping between account addresses and account states. The world state can be stored in data structures such as the Merkle Patricia tree (MPT). 
     Besides state data, blockchain networks can also store other types of data such as block data and index data. Block data can include block header and block body. The block header can include identity information of a particular block and the block body can include transactions that are confirmed with the block. As transactions are increasingly entered into the blockchain, state data and block data can grow very large in size. In some DLSs, every node stores an entire copy of the blockchain, which can take large amount of storage space. This is because all block data and state data are stored going back to the first transaction recorded to the blockchain. In some DLSs, a few shared nodes store the entire copy of the blockchain and share blockchain data with other blockchain nodes which can create “data inequality.” That is, when data are unevenly distributed across different nodes, the risk of data security can be high when nodes that store majority of data are at fault. 
     Accordingly, it would be desirable to enable such storage in a manner that maintains data equality and data processing efficiency. It would also be desirable to enable storage of data on nodes in the DLS in a manner that reduces consumption of computational resources or memory, while being able to recover and retrieve the original data when needed. In some cases, when new blockchain nodes are added to a blockchain network, it would be desirable to enable the new blockchain nodes to share the data storage burden; hence reducing storage consumption of existing blockchain nodes. 
     SUMMARY 
     Described embodiments of the subject matter can include one or more features, alone or in combination. 
     For example, in one embodiment, a computer-implemented method for blockchain data storage performed by a blockchain node is disclosed. The blockchain node can receive a request for performing error correction coding (ECC) to one or more blocks of a blockchain, obtain the one or more blocks based on blockchain data received from at least one blockchain node of the blockchain network, and perform ECC of the one or more blocks to generate one or more encoded blocks, wherein a code rate of the one or more encoded blocks equals a minimum number of honest blockchain nodes required by the blockchain network and a total number of blockchain nodes of the blockchain network. 
     In some embodiments, these general and specific aspects may be implemented using a system, a method, or a computer program, or any combination of systems, methods, and computer programs. The foregoing and other described embodiments can each, optionally, include one or more of the following features: 
     In some embodiments, the blockchain data received from the at least one blockchain node are a plurality of datasets divided from an ECC encoded version of the one or more blocks, and the obtaining the one or more blocks further comprises, identifying one or more datasets divided from the ECC encoded version of the one or more blocks that are stored locally in the blockchain node, and decoding the one or more blocks based on the one or more datasets that are stored locally and the plurality of datasets received from the at least one blockchain node. 
     In some embodiments, the at least one blockchain node is at least one full blockchain node, and wherein the obtaining the one or more blocks further comprises retrieving the one or more blocks from the at least one full blockchain node. 
     In some embodiments, the one or more blocks are first one or more blocks, and retrieving the first one or more blocks further comprises: sending hash values of the first one or more blocks to the at least one full blockchain node, receiving second one or more blocks from the at least one full blockchain node, and determining the second one or more blocks are authentic if hash values of the second one or more blocks are same as hash values of the first one or more blocks. 
     In some embodiments, the request includes the code rate and instructions to divide each encoded block of the one or more encoded blocks to a plurality of datasets and to assign the plurality of datasets to the blockchain nodes of the blockchain network. 
     In some embodiments, for each encoded block of the one or more encoded blocks, the blockchain node can further divide the encoded block into the plurality of datasets according to the instructions, and store at least one of the plurality of datasets assigned to the blockchain node according to the instructions. 
     In some embodiments, the blockchain node can further hash a remainder of the plurality of datasets other than the at least one of the plurality of datasets assigned to the blockchain node to generate hash values corresponding to the remainder of the plurality of datasets, store the hash values, and delete the one or more blocks and the remainder of the plurality of datasets. 
     In some embodiments, the request is a first request and the one or more encoded blocks are first one or more encoded blocks, the blockchain node can further receive a second request for performing ECC to the one or more blocks of a blockchain in response to a new blockchain node storing the one or more blocks being added to the blockchain network, retrieve the one or more blocks from the new blockchain node, and perform ECC of the one or more blocks to generate second one or more encoded blocks, wherein a code rate of the second one or more encoded blocks equals a minimum number of honest blockchain nodes required by the blockchain network and a total number of blockchain nodes after the new blockchain node is added. 
     In some embodiments, the new blockchain nodes are full nodes that store a copy of the blockchain. 
     In some embodiments, the ECC is performed when utilization rate of computational resource of the blockchain node is less than or equal to a predetermined value. 
     In some embodiments, the ECC is erasure coding performed by adding redundant bits to the one or more blocks. 
     It is appreciated that methods in accordance with this specification may include any combination of the aspects and features described herein. That is, methods in accordance with this specification are not limited to the combinations of aspects and features specifically described herein, but also include any combination of the aspects and features provided. 
     The details of one or more embodiments of this specification are set forth in the accompanying drawings and the description below. Other features and advantages of this specification will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an example of an environment that can be used to execute embodiments of this specification. 
         FIG. 2  depicts an example of an architecture in accordance with embodiments of this specification. 
         FIG. 3  depicts an example of a block data encoding and hashing process in accordance with embodiments of this specification. 
         FIG. 4  depicts an example of a data storage scheme in accordance with embodiments of this specification. 
         FIG. 5  depicts another example of a block data encoding and hashing process in accordance with embodiments of this specification. 
         FIG. 6  depicts an example of adding blockchain nodes to a blockchain network in accordance with embodiments of this specification. 
         FIG. 7  depicts an example of a process that can be executed in accordance with embodiments of this specification. 
         FIG. 8  depicts examples of modules of an apparatus in accordance with embodiments of this specification. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     This specification describes technologies for processing blockchain data for storage based on error correction code (ECC). These technologies generally involve receiving a request for performing error correction coding (ECC) to one or more blocks of a blockchain, obtaining the one or more blocks based on blockchain data received from at least one blockchain node of the blockchain network, and performing ECC of the one or more blocks to generate one or more encoded blocks, wherein a code rate of the one or more encoded blocks equals a minimum number of honest blockchain nodes required by the blockchain network and a total number of blockchain nodes of the blockchain network. 
     As described herein, blockchain networks can store different types of data such as state data, block data, and index data. Block data includes all transactions in the blockchain network, which can take a large amount of storage space as new blocks are constantly adding to the blockchain. It can be inefficient for the blockchain nodes to each store all the block data, especially for data of infrequently accessed blocks (e.g., blocks added to the blockchain long time ago). Accordingly, embodiments of this specification provide that each blockchain node stores a portion of infrequently accessed blocks and retrieves the rest of the block data from other blockchain nodes when needed, to reduce storage consumption. However, if faulty nodes or unreliable nodes exist in the blockchain network, the retrieved data cannot be trusted and data loss may occur. 
     In some embodiments, the blockchain nodes can perform ECC, such as erasure coding, to encode the infrequently accessed blocks. The ECC encoded blocks can then be divided into a plurality of datasets. The plurality of datasets can be indexed and assigned to different blockchain nodes to store based on a data storage scheme. When data from an infrequently accessed block is needed by a blockchain node to execute a smart contract, the blockchain node can retrieve corresponding datasets from other blockchain nodes based on the index to form the ECC encoded block and recover the original block. By sharing ECC encoded blocks, even if unauthentic data exists or data loss occurs, the original block data can be recovered as long as the percentage of honest blockchain nodes is greater than or equal to the code rate of the ECC. 
     In some embodiments, new blockchain nodes are added as full nodes to a blockchain network. The newly added full nodes store additional copies of blocks that are not shared by other nodes. The additional copies of blocks can add redundancy to the blockchain network in terms of storage. Embodiments of this specification provide techniques to reperform ECC to the blocks and share the encoded blocks with other blockchain nodes to reduce storage consumption. The ECC can also be reperformed by the blockchain node when the CPU usage is low so as better utilize the computational resources. 
     The techniques described in this specification produce several technical effects. For example, embodiments of the subject matter reduce the burden on storage resources of blockchain networks, while maintaining computational efficiency and data equality of the blockchain nodes. For infrequently accessed blocks (e.g., older blocks), storage resources of blockchain nodes can be conserved by saving only a portion of error correction coding (ECC) encoded blocks (also referred to herein as encoded blocks) on each blockchain node and retrieving the remainder of the encoded blocks from other blockchain nodes when needed. 
     In some embodiments, an ECC encoded block can be divided to a plurality of datasets. A blockchain node can store a selected portion of the plurality of datasets and hash values corresponding to the remainder of the datasets. The selection can be based on a data storage scheme agreed to by blockchain nodes of the blockchain network. The plurality of datasets and the hash values can be indexed by a block ID associated with the ECC encoded block. When data from the block needs to be accessed by the blockchain node, it can retrieve the remainder of the datasets from other blockchain nodes. The blockchain node can send corresponding hash values to the other blockchain nodes to retrieve the remainder of the datasets. Since hash values are irreversible, the blockchain node can verify whether the received data are authentic by hashing the received data and comparing the hashed values with hash values that are locally stored. As such, data security can be ensured and faulty nodes can be identified. Even if the blockchain node receives unauthentic data from faulty blockchain nodes, the corresponding block can be recovered as long as the percentage of the unauthentic data is less than or equal to the maximum fraction of erroneous or missing bits allowed by the ECC. 
     In some cases, new blockchain nodes are added as full nodes to a blockchain network. The newly added full nodes store additional copies of blocks that are not shared by other nodes. The additional copies of blocks add redundancy to the blockchain network in terms of storage. In such cases, ECC can be reperformed to the blocks with higher code rate to reduce redundancy and storage consumption. Reperforming ECC can be executed when the CPU usage is low so as better utilize the computational resources. 
     To provide further context for embodiments of this specification, and as introduced above, distributed ledger systems (DLSs), which can also be referred to as consensus networks (e.g., made up of peer-to-peer nodes), and blockchain networks, enable participating entities to securely, and immutably conduct transactions, and store data. Although the term blockchain is generally associated with particular networks, and/or use cases, blockchain is used herein to generally refer to a DLS without reference to any particular use case. 
     A blockchain is a data structure that stores transactions in a way that the transactions are immutable. Thus, transactions recorded on a blockchain are reliable and trustworthy. A blockchain includes one or more blocks. Each block in the chain is linked to a previous block immediately before it in the chain by including a cryptographic hash of the previous block. Each block also includes a timestamp, its own cryptographic hash, and one or more transactions. The transactions, which have already been verified by the nodes of the blockchain network, are hashed and encoded into a Merkle tree. A Merkle tree is a data structure in which data at the leaf nodes of the tree is hashed, and all hashes in each branch of the tree are concatenated at the root of the branch. This process continues up the tree to the root of the entire tree, which stores a hash that is representative of all data in the tree. A hash purporting to be of a transaction stored in the tree can be quickly verified by determining whether it is consistent with the structure of the tree. 
     Whereas a blockchain is a decentralized or at least partially decentralized data structure for storing transactions, a blockchain network is a network of computing nodes that manage, update, and maintain one or more blockchains by broadcasting, verifying and validating transactions, etc. As introduced above, a blockchain network can be provided as a public blockchain network, a private blockchain network, or a consortium blockchain network. Embodiments of this specification are described in further detail herein with reference to a consortium blockchain network. It is contemplated, however, that embodiments of this specification can be realized in any appropriate type of blockchain network. 
     In general, a consortium blockchain network is private among the participating entities. In a consortium blockchain network, the consensus process is controlled by an authorized set of nodes, which can be referred to as consensus nodes, one or more consensus nodes being operated by a respective entity (e.g., a financial institution, insurance company). For example, a consortium of ten (10) entities (e.g., financial institutions, insurance companies) can operate a consortium blockchain network, each of which operates at least one node in the consortium blockchain network. 
     In some examples, within a consortium blockchain network, a global blockchain is provided as a blockchain that is replicated across all nodes. That is, all consensus nodes are in perfect state consensus with respect to the global blockchain. To achieve consensus (e.g., agreement to the addition of a block to a blockchain), a consensus protocol is implemented within the consortium blockchain network. For example, the consortium blockchain network can implement a practical Byzantine fault tolerance (PBFT) consensus, described in further detail below. 
       FIG. 1  is a diagram illustrating an example of an environment  100  that can be used to execute embodiments of this specification. In some examples, the environment  100  enables entities to participate in a consortium blockchain network  102 . The environment  100  includes computing devices  106 ,  108 , and a network  110 . In some examples, the network  110  includes a local area network (LAN), wide area network (WAN), the Internet, or a combination thereof, and connects web sites, user devices (e.g., computing devices), and back-end systems. In some examples, the network  110  can be accessed over a wired and/or a wireless communications link. In some examples, the network  110  enables communication with, and within the consortium blockchain network  102 . In general, the network  110  represents one or more communication networks. In some cases, the computing devices  106 ,  108  can be nodes of a cloud computing system (not shown), or each computing device  106 ,  108  can be a separate cloud computing system including a number of computers interconnected by a network and functioning as a distributed processing system. 
     In the depicted example, the computing systems  106 ,  108  can each include any appropriate computing system that enables participation as a node in the consortium blockchain network  102 . Examples of computing devices include, without limitation, a server, a desktop computer, a laptop computer, a tablet computing device, and a smartphone. In some examples, the computing systems  106 ,  108  host one or more computer-implemented services for interacting with the consortium blockchain network  102 . For example, the computing system  106  can host computer-implemented services of a first entity (e.g., user A), such as a transaction management system that the first entity uses to manage its transactions with one or more other entities (e.g., other users). The computing system  108  can host computer-implemented services of a second entity (e.g., user B), such as a transaction management system that the second entity uses to manage its transactions with one or more other entities (e.g., other users). In the example of  FIG. 1 , the consortium blockchain network  102  is represented as a peer-to-peer network of nodes, and the computing systems  106 ,  108  provide nodes of the first entity, and second entity respectively, which participate in the consortium blockchain network  102 . 
       FIG. 2  depicts an example of an architecture  200  in accordance with embodiments of this specification. The example conceptual architecture  200  includes participant systems  202 ,  204 ,  206  that correspond to Participant A, Participant B, and Participant C, respectively. Each participant (e.g., user, enterprise) participates in a blockchain network  212  provided as a peer-to-peer network including a plurality of nodes  214 , at least some of which immutably record information in a blockchain  216 . Although a single blockchain  216  is schematically depicted within the blockchain network  212 , multiple copies of the blockchain  216  are provided, and are maintained across the blockchain network  212 , as described in further detail herein. 
     In the depicted example, each participant system  202 ,  204 ,  206  is provided by, or on behalf of Participant A, Participant B, and Participant C, respectively, and functions as a respective node  214  within the blockchain network. As used herein, a node generally refers to an individual system (e.g., computer, server) that is connected to the blockchain network  212 , and enables a respective participant to participate in the blockchain network. In the example of  FIG. 2 , a participant corresponds to each node  214 . It is contemplated, however, that a participant can operate multiple nodes  214  within the blockchain network  212 , and/or multiple participants can share a node  214 . In some examples, the participant systems  202 ,  204 ,  206  communicate with, or through the blockchain network  212  using a protocol (e.g., hypertext transfer protocol secure (HTTPS)), and/or using remote procedure calls (RPCs). 
     Nodes  214  can have varying degrees of participation within the blockchain network  212 . For example, some nodes  214  can participate in the consensus process (e.g., as miner nodes that add blocks to the blockchain  216 ), while other nodes  214  do not participate in the consensus process. As another example, some nodes  214  store a complete copy of the blockchain  216 , while other nodes  214  only store copies of portions of the blockchain  216 . For example, data access privileges can limit the blockchain data that a respective participant stores within its respective system. In the example of  FIG. 2 , the participant systems  202 ,  204 , and  206  store respective, complete copies  216 ′,  216 ″, and  216 ′″ of the blockchain  216 . 
     A blockchain (e.g., the blockchain  216  of  FIG. 2 ) is made up of a chain of blocks, each block storing data. Examples of data include transaction data representative of a transaction between two or more participants. While transactions are used herein by way of non-limiting example, it is contemplated that any appropriate data can be stored in a blockchain (e.g., documents, images, videos, audio). Examples of a transaction can include, without limitation, exchanges of something of value (e.g., assets, products, services, currency). The transaction data is immutably stored within the blockchain. That is, the transaction data cannot be changed. 
     Before storing in a block, the transaction data is hashed. Hashing is a process of transforming the transaction data (provided as string data) into a fixed-length hash value (also provided as string data). It is not possible to un-hash the hash value to obtain the transaction data. Hashing ensures that even a slight change in the transaction data results in a completely different hash value. Further, and as noted above, the hash value is of fixed length. That is, no matter the size of the transaction data the length of the hash value is fixed. Hashing includes processing the transaction data through a hash function to generate the hash value. An example of a hash function includes, without limitation, the secure hash algorithm (SHA)-256, which outputs 256-bit hash values. 
     Transaction data of multiple transactions are hashed and stored in a block. For example, hash values of two transactions are provided, and are themselves hashed to provide another hash. This process is repeated until, for all transactions to be stored in a block, a single hash value is provided. This hash value is referred to as a Merkle root hash, and is stored in a header of the block. A change in any of the transactions will result in change in its hash value, and ultimately, a change in the Merkle root hash. 
     Blocks are added to the blockchain through a consensus protocol. Multiple nodes within the blockchain network participate in the consensus protocol, and perform work to have a block added to the blockchain. Such nodes are referred to as consensus nodes. PBFT, introduced above, is used as a non-limiting example of a consensus protocol. The consensus nodes execute the consensus protocol to add transactions to the blockchain, and update the overall state of the blockchain network. 
     In further detail, the consensus node generates a block header, hashes all of the transactions in the block, and combines the hash value in pairs to generate further hash values until a single hash value is provided for all transactions in the block (the Merkle root hash). This hash is added to the block header. The consensus node also determines the hash value of the most recent block in the blockchain (i.e., the last block added to the blockchain). The consensus node also adds a nonce value, and a timestamp to the block header. 
     In general, PBFT provides a practical Byzantine state machine replication that tolerates Byzantine faults (e.g., malfunctioning nodes, malicious nodes). This is achieved in PBFT by assuming that faults will occur (e.g., assuming the existence of independent node failures, and/or manipulated messages sent by consensus nodes). In PBFT, the consensus nodes are provided in a sequence that includes a primary consensus node, and backup consensus nodes. The primary consensus node is periodically changed. Transactions are added to the blockchain by all consensus nodes within the blockchain network reaching an agreement as to the world state of the blockchain network. In this process, messages are transmitted between consensus nodes, and each consensus nodes proves that a message is received from a specified peer node, and verifies that the message was not modified during transmission. 
     In PBFT, the consensus protocol is provided in multiple phases with all consensus nodes beginning in the same state. To begin, a client sends a request to the primary consensus node to invoke a service operation (e.g., execute a transaction within the blockchain network). In response to receiving the request, the primary consensus node multicasts the request to the backup consensus nodes. The backup consensus nodes execute the request, and each sends a reply to the client. The client waits until a threshold number of replies are received. In some examples, the client waits for f+1 replies to be received, where f is the maximum number of faulty consensus nodes that can be tolerated within the blockchain network. In PBFT, the maximum number of faulty consensus nodes needs to be less than 1/3 of the total number of consensus nodes. The final result is that a sufficient number of consensus nodes come to an agreement on the order of the record that is to be added to the blockchain, and the record is either accepted, or rejected. 
     In some blockchain networks, cryptography is implemented to maintain privacy of transactions. For example, if two nodes want to keep a transaction private, such that other nodes in the blockchain network cannot discern details of the transaction, the nodes can encrypt the transaction data. An example of cryptography includes, without limitation, symmetric encryption, and asymmetric encryption. Symmetric encryption refers to an encryption process that uses a single key for both encryption (generating ciphertext from plaintext), and decryption (generating plaintext from ciphertext). In symmetric encryption, the same key is available to multiple nodes, so each node can en-/de-crypt transaction data. 
     Asymmetric encryption uses keys pairs that each include a private key, and a public key, the private key being known only to a respective node, and the public key being known to any or all other nodes in the blockchain network. A node can use the public key of another node to encrypt data, and the encrypted data can be decrypted using other node&#39;s private key. For example, and referring again to  FIG. 2 , Participant A can use Participant B&#39;s public key to encrypt data, and send the encrypted data to Participant B. Participant B can use its private key to decrypt the encrypted data (ciphertext) and extract the original data (plaintext). Messages encrypted with a node&#39;s public key can only be decrypted using the node&#39;s private key. 
     Asymmetric encryption is used to provide digital signatures, which enables participants in a transaction to confirm other participants in the transaction, as well as the validity of the transaction. For example, a node can digitally sign a message, and another node can confirm that the message was sent by the node based on the digital signature of Participant A. Digital signatures can also be used to ensure that messages are not tampered with in transit. For example, and again referencing  FIG. 2 , Participant A is to send a message to Participant B. Participant A generates a hash of the message, and then, using its private key, encrypts the hash to provide a digital signature as the encrypted hash. Participant A appends the digital signature to the message, and sends the message with digital signature to Participant B. Participant B decrypts the digital signature using the public key of Participant A, and extracts the hash. Participant B hashes the message and compares the hashes. If the hashes are same, Participant B can confirm that the message was indeed from Participant A, and was not tampered with. 
       FIG. 3  depicts an example of a block data encoding and hashing process  300  in accordance with embodiments of this specification. In this example, a blockchain network of four blockchain nodes is depicted, which are blockchain nodes  302 ,  304 ,  306 , and  308 . Using blockchain node  302  as an example to illustrate the encoding and hashing process  300 , the blockchain node  302  can store block data of the blockchain network to block body of a block  312 . In the illustrated example, the block data is stored in block  100 . Afterwards, the blockchain node  302  can engage in a consensus process with other blockchain nodes  304 ,  306 , and  308 . During the consensus process, the blockchain node  302  can perform a consensus algorithm, such as proof of work (PoW) or proof of stake (PoS) to create a corresponding block on the blockchain. 
     In some embodiments, the blockchain node  302  can identify one or more infrequently accessed blocks. In practice, the longer a block has been created, the less likely the corresponding block data is needed for operations such as executing smart contracts. The blockchain node  302  can determine that locally stored blocks are infrequently accessed when they are historical blocks that have been created on the blockchain for a predetermined amount of time. For example, the predetermined amount of time can be one or two times of the average time a block is created. In some examples, a block can also be determined as infrequently accessed when no block data in the block is retrieved for the predetermined amount of time to execute smart contracts. 
     After identifying infrequently accessed blocks, the blockchain node  302  can perform ECC  314  of block data in the block body of each of the infrequently accessed blocks. ECC can be used for controlling errors or losses of data over unreliable transmissions by adding redundant bits (also referred to as redundancy) to the data. Redundant bits can be a complex function of many original information bits. The redundancy can allow errors or losses of data to be corrected without retransmission of the data. The original information may or may not appear literally in the encoded output. ECC codes that include the unmodified original information in the encoded output are referred to as systematic ECC codes, while those that do not are referred to as non-systematic ECC codes. The maximum fractions of errors or of missing bits that can be corrected by ECC is determined by the design of the ECC code. Therefore, different error correction codes are suitable for different conditions. In general, a stronger ECC code induces more redundancy, which increases storage consumption of the code and reduces communication efficiency if the encoded information is to be transmitted. 
     One example ECC can be the erasure coding. Using the erasure coding, a message of k symbols can be encoded to a codeword with n symbols, where k and n are natural numbers, and k&lt;n. The message can be recovered from a subset of the n-symbol codeword. The fraction r=k/n is the code rate of the erasure code. 
     By using ECC, each of the blockchain nodes can store a portion of the encoded block data and retrieve the rest of the encoded block data from other blockchain nodes when needed. In some embodiments, the ECC can be performed when utilization rate of computational resource of the blockchain node  302  is lower than a predetermined value (e.g., 40%). As such, the interference with other computational operations on the blockchain node  302  can be reduced. In some embodiments, ECC can be performed when the usage of storage space of the blockchain node  302  is greater than or equal to a predetermined percentage, such that after ECC, some portions of the encoded block data can be deleted to free up storage space. 
     Again, using block  100  as an example, assuming that the blockchain node  302  determines the block  100  as an infrequently accessed block and performs ECC  314 , the ECC encoded data can be divided into a plurality of datasets based on a data storage scheme. A data storage scheme can be provided as a set of computer-executable instructions that define where and/or how data is to be stored within the blockchain network. In some examples, the data storage scheme can be provided by a trusted node with proof of authority and agreed to by the blockchain nodes. In some examples, the data storage scheme can be agreed to by the blockchain nodes through consensus. Generally, the data storage scheme can include one or more predetermined rules for dividing the encoded data to a plurality of datasets based on the number of blockchain nodes in a blockchain network. The data storage scheme can also include assignments of one or more datasets of the plurality of datasets to be stored or hashed by each of the blockchain nodes. To ensure data equality, the data storage scheme can include an assignment of at least one dataset to be stored by each blockchain node of the blockchain network. 
     In the example shown in  FIG. 3 , the encoded block data of block  100  is divided into four datasets, which are Data 1 , Data 2 , Data 3 , and Vdata 1 , each to be stored by one of the blockchain nodes  302 ,  304 ,  306 , and  308 . Vdata 1  can represent the redundant bits of the ECC for error correction. Data 1  is selected to be stored by the blockchain node  302  according to the data storage scheme. Data 2 , Data 3 , and Vdata 1  are selected to be separately hashed  316  to generate hash values Dhash 2 , Dhash 3 , and Vhash 1 , respectively. In accordance with embodiments of this specification, the encoded data can be divided to more than four datasets when the blockchain network has more than four nodes. In some examples, each of the blockchain nodes can store more than one dataset and hash the rest of the datasets assigned to be stored by other nodes. 
     Referring now to  FIG. 4 ,  FIG. 4  depicts an example of a data storage scheme  400  in accordance with embodiments of this specification. As discussed earlier, Data 1  is selected to be stored by the blockchain node  302  according to the data storage scheme  400 . Based on the data storage scheme  400 , blockchain node  304  stores Data 2  and separately hashes Data 1 , Data 3 , and Vdata 1  to generate hash values Dhash 1 , Dhash 3 , and Vhash 1 , respectively. Blockchain node  306  stores Data 3  and separately hashes Data 1 , Data 2 , and Vdata 1  to generate hash values Dhash 1 , Dhash 2  and Vhash 1 , respectively. Blockchain node  308  stores Vdata 1  and separately hashes Data 1 , Data 2 , and Vdata 3  to generate hash values Dhash 1 , Dhash 2  and Dhash 3 , respectively. 
     Referring back to  FIG. 3 , because the hash values correspond to encoded datasets of the same block, they can be indexed by a block ID of the block. For example, the blockchain node  302  can index Data 1 , Dhash 1 , Dhash 2 , and Vhash 1  associated with block  100  with a block ID  100 . As such, the blockchain node  302  can use the indexed block ID to map the hash values to their corresponding blocks. A more detailed example of indexing the datasets and hash values is discussed in the description of  FIG. 6 . 
     It is to be understood that other data storage schemes can be made for the blockchain nodes  302 ,  304 ,  306 , and  308 , according to the data storage scheme. In some examples, the encoded block data of block  100  can be divided to more than four datasets. It is to be understood that other data storage schemes can be made for the blockchain nodes  502 ,  504 ,  506 , and  508 , according to the data storage scheme. 
     After generating and storing Dhash 2 , Dhash 3 , and Vhash 1 , the blockchain node  302  can delete Data 2 , Data 3 , and Vdata 1  from storage to save storage space. As such, for each block, the blockchain node  302  only stores one ECC encoded dataset (i.e., Data 1 ) and three hash values (i.e., Dhash 2 , Dhash 3 , and Vhash 1 ), instead of the entire block. As such, storage space can be significantly reduced. Similar to block  100 , the encoding and hashing process can be performed for other infrequently accessed blocks that are stored by the blockchain nodes  304 ,  306 , and  308 . 
     When the blockchain node  302  determines that block data of the block  100  is needed for executing a smart contract, it can retrieve Data 2 , Data 3 , and Vdata 1  from blockchain nodes  304 ,  306 , and  308 , respectively, according to the data storage scheme. To retrieve datasets from other blockchain nodes  304 ,  306 , and  308 , blockchain node  302  can send hash values corresponding to the datasets to be retrieved according to the data storage scheme. 
     For example, to retrieve Data 2 , the blockchain node  302  can send Dhash 2  to the blockchain node  304 . If the blockchain node  304  has Data 2  stored, it can send the Data 2  back to the blockchain node  302  in response to receiving the Dhash 2 . After receiving the Data 2  from the blockchain node  304 , the blockchain node  302  can hash the received dataset and compare the hash value with Dhash 2 . If the hash value is the same as Dhash 2 , the blockchain node  302  can determine that the received dataset is authentic. Otherwise, the received dataset is determined to be unauthentic. When the received dataset is determined as unauthentic, the blockchain node  302  can report the blockchain node  304  as a faulty node (or a Byzantine node). If the percentage of unauthentic data received by the blockchain node  302  is less than or equal to the maximum fraction of erroneous or missing bits that can be corrected by the ECC, block  100  can be recovered from the locally stored and received datasets. 
     As described earlier, blockchain networks can store different types of data such as state data, block data, and index data. State data are often stored as a content-addressed state tree, such as the MPT or the fixed depth Merkle tree (FDMT). Content-addressed state trees are incremental in nature. That is, changes of account states are reflected by adding new tree structures instead of only updating values of the existing state tree. Therefore, the content-addressed state trees can grow very large in size when blocks are continuously added to the blockchain. Under the FDMT storage scheme, state data can be separated into current state data associated with the current block and historic state data associated with all blocks of the blockchain. Most data in the FDMT are infrequently used historic state data. Storing all historic state data in every consensus node can be quite inefficient in terms of storage resource usage. 
     In some embodiments, similar to encoding and sharing block data, ECC such as erasure coding can be used to encode the historic state data. Each consensus node in the blockchain network stores only a portion of the historic state data and retrieves the rest of the historic state data from other nodes to reduce storage consumption. By sharing ECC encoded historic state data instead of the original historic state data, even if unauthentic data exists or data loss occurs, the original historic state data can be recovered, as long as the percentage of unauthentic data or data loss is less than or equal to the maximum fraction of erroneous or missing bits that can be corrected by the ECC. 
       FIG. 5  depicts another example of a block data encoding and hashing process  500  in accordance with embodiments of this specification. In this example, a blockchain network of four blockchain nodes is depicted, which are blockchain nodes  502 ,  504 ,  506 , and  508 . Using blockchain node  502  as an example to illustrate the encoding and hashing process  500 , when new block data are added to the block  512 , the blockchain node  502  can perform ECC  514  to encode the block data. As compared to the encoding and hashing process  300  discussed in the description of  FIG. 3 , the blockchain node  502  performs ECC on the block data as they are written to a block. As such, the blockchain node  502  does not need to store the entire block, but can instead, store a selected portion of the ECC encoded block data and hash values corresponding to the rest of the encoded block data based on the data storage scheme. This encoding and hashing process  500  can be especially suitable for scenarios when blockchain node  502  has low disk space. 
     In some embodiments, instead of storing data as blocks, the blockchain node  502  can store a write-ahead log (WAL) file or other similar roll-forward journal files. The WAL file can record block data that have been committed but not yet stored by the blockchain node  502 . Using the WAL file, the original blockchain data can be preserved in the database file, while changes of the blockchain data can be written into a separate WAL file. A commit to roll-forward with the changes can happen without ever writing to the original blockchain data. This arrangement allows continued operations of the blockchain data while changes are committed into the WAL file. By using the WAL file to store changes made through the encoding and hashing process  500 , the blockchain node  502  can indicate that it has the block data for consensus, while performing the ECC in the background when appropriate. As such, the ECC can be performed when utilization rate of computational resource of the blockchain node  302  is low, in order to reduce the impact on computational efficiency or latency of the consensus process. 
     In some embodiments, the blockchain node  502  can store the block data in a buffer. The blockchain node  502  can perform ECC to the block data stored in the buffer when the size of the data is greater than a predetermined threshold or when the buffer is full. After performing ECC, the blockchain node  502  can follow the encoding and hashing process  500  to store encoded block data and hash values, as discussed in the description below. 
     Using block  100  as an example again, after performing the ECC, the encoded block data can be divided into a plurality of datasets based on the data storage scheme. Similar to the example discussed in the description of  FIG. 3 , the encoded block data of block  100  can be divided into four datasets, which are Data 1 , Data 2 , Data 3 , and Vdata 1 , each to be stored by one of the blockchain nodes  502 ,  504 ,  506 , and  508 . Vdata 1  can represent the redundant bits of the ECC. Data 1  is selected to be stored by the blockchain node  502  according to the data storage scheme. Data 2 , Data 3 , and Vdata 1  are selected to be separately hashed  516  to generate hash values Dhash 2 , Dhash 3 , and Vhash 1 , respectively. 
     The hash values can be indexed by a block ID of a corresponding block of the hash values. For example, the blockchain node  502  can index Data 1 , Dhash 1 , Dhash 2 , and Vhash 1  associated with block  100  with a block ID  100 . As such, the blockchain node  502  can use the indexed block ID to map the hash values to their corresponding blocks. A more detailed example of indexing the datasets and hash values is discussed in the description of  FIG. 6 . 
     It is to be understood that other data storage schemes can be made for the one or more blockchain nodes  502 ,  504 ,  506 , and  508 , according to the data storage scheme. For example, the encoded block data of block  100  can be divided into more than four datasets. Each of the blockchain nodes  502 ,  504 ,  506 , and  508  can store more than one dataset and hash the rest of the datasets stored by other nodes. 
     After generating Dhash 2 , Dhash 3 , and Vhash 1 , the blockchain node  502  can store Data 1 , Dhash 2 , Dhash 3 , and Vhash 1  and delete Data 2 , Data 3 , and Vdata 1  from storage to save storage space. As such, for each block of the blockchain, the blockchain node  502  only stores one dataset (i.e., Data 1 ) and three hash values (i.e., Dhash 2 , Dhash 3 , and Vhash 1 ) of the ECC encoded block data instead of the original block data to save on storage space. When the blockchain node  502  determines that block data of the block  100  is needed for executing a smart contract, it can retrieve Data 2 , Data 3 , and Vdata 1  from blockchain nodes  504 ,  506 , and  508 , respectively, according to the data storage scheme. 
     To retrieve datasets from other blockchain nodes  504 ,  506 , and  508 , blockchain node  502  can send hash values corresponding to the datasets to be retrieved according to the data storage scheme. For example, to retrieve Data 2 , the blockchain node  502  can send Dhash 2  to the blockchain node  504 . If the blockchain node  504  has Data 2  stored, it can send the Data 2  back to the blockchain node  502  in response to receiving the Dhash 2 . After receiving the Data 2  from the blockchain node  504 , the blockchain node  502  can hash the received dataset and compare the hash value with Dhash 2 . If the hash value is the same as Dhash 2 , the blockchain node  502  can determine that the received dataset is authentic. Otherwise, the received dataset can be determined as unauthentic. When the received dataset is determined as unauthentic, the blockchain node  502  can report the blockchain node  504  as a faulty node (or a Byzantine node). If the percentage of unauthentic data received by the blockchain node  502  is less than or equal to the maximum fraction of erroneous or missing bits that can be corrected by the ECC, block  100  can be recovered from the locally stored and received datasets. 
     As discussed earlier, by performing the encoding and hashing process, blockchain data can be ECC encoded and divided into a plurality of datasets. To save on storage space, each blockchain node can store one or more of the plurality of datasets and hash values of rest of the datasets based on a data storage scheme. The stored datasets and hash values can be indexed with Block IDs in order for a blockchain node to retrieve datasets from other nodes to recover original data. 
       FIG. 6  depicts an example  600  of adding blockchain nodes to a blockchain network in accordance with embodiments of this specification. As discussed earlier, the encoding and hashing process can be performed to effectively reduce storage consumption of a blockchain network. Under the PBFT consensus protocol, if the total number of blockchain nodes is denoted by N, the number of faulty blockchain nodes is denoted by f, then N&gt;3f must satisfy for the blockchain network to be Byzantine fault tolerant. For example, in a four-node blockchain network, the maximum number of faulty nodes tolerable by the blockchain network is 1 under the PBFT consensus protocol. As such, if the blockchain nodes perform ECC to the original blockchain data (or original data) with a code rate of no greater than 3/4 (i.e., the proportion of the original data is no more than 3/4 of the total encoded data), and each stores a quarter of the encoded blockchain data (or encoded), the original data can be recovered even if one of the blockchain nodes is a faulty node. The redundancy rate can be defined as a total volume of encoded data and original data stored by the blockchain nodes of the blockchain network divided by the volume of a copy of the original data. In this example, since no blockchain node stores the original data, the redundancy rate is the inverse of the code rate (i.e., the volume of encoded data divided by the original data), which is 4/3. 
     In the depicted example  600 , it is assumed that when blocks  1  to  100  are generated, there are four blockchain nodes, nodes  1 ,  2 ,  3 , and  4 , in the blockchain network. Under PBFT consensus protocol, the minimum number of honest blockchain nodes required by the blockchain network is three. Applying the Encoding and hashing process as discussed in the descriptions of  FIGS. 3 and 5 , blocks  1  to  100  can each be encoded with a maximum code rate of 3/4. The encoded blocks can each be divided into three datasets of original data and one dataset of redundant bits to be stored by the four blockchain nodes. 
     Node  5  is added to the blockchain network as a full node during the generation of block  101 . That is, Node  5  stores an entire copy of blocks  1  to  100 , but participates in the Encoding and hashing process with the four existing blockchain nodes starting from the generation of block  101 . Assuming that the blockchain network has five blockchain nodes during the generation of blocks  101  to  200 , the minimum number of honest blockchain nodes required by the blockchain network is four under the PBFT consensus protocol. As such, blocks  101  to  200  can each be encoded with a maximum code rate of 4/5. The encoded blocks can each be divided into four datasets of original data and one dataset of redundant bits to be stored by the five blockchain nodes in the blockchain network. 
     Node  6  is added to the blockchain network as a full node during the generation of block  201 . That is, Node  6  stores an entire copy of blocks  1  to  200 , but participates in the Encoding and hashing process with other blockchain nodes of the blockchain network since the generation of block  201 . Assuming that the blockchain network has six blockchain nodes during the generation of blocks  201  to  300 , the minimum number of honest blockchain nodes required by the blockchain network is five under the PBFT consensus protocol. As such, blocks  201  to  300  can each be encoded with a maximum code rate of 5/6. The encoded blocks can each be divided into four datasets of original data and two datasets of redundant bits to be stored by the six blockchain nodes in the blockchain network. 
     Node  7  is added to the blockchain network as a full node during the generation of block  301 . That is, Node  7  stores an entire copy of blocks  1  to  300 , but participates in the Encoding and hashing process with other blockchain nodes of the blockchain network since the generation of block  301 . Assuming that the blockchain network has seven blockchain nodes during the generation of blocks  301  to  400 , the minimum number of honest blockchain nodes required by the blockchain network is five under the PBFT consensus protocol. As such, blocks  301  to  400  can each be encoded with a maximum code rate of 5/7. The encoded blocks can each be divided into five datasets of original data and two datasets of redundant bits to be stored by the seven blockchain nodes in the blockchain network. 
     Node  8  is added to the blockchain network as a full node during the generation of block  401 . That is, Node  8  stores an entire copy of blocks  1  to  400 , but participates in the Encoding and hashing process with other blockchain nodes of the blockchain network since the generation of block  401 . Assuming that the blockchain network has eight blockchain nodes during the generation of blocks  401  to  500 , the minimum number of honest blockchain nodes required by the blockchain network is six under the PBFT consensus protocol. As such, blocks  401  to  500  can each be encoded with a maximum code rate of 3/4. The encoded blocks can each be divided into six datasets of original data and two datasets of redundant bits to be stored by the eight blockchain nodes in the blockchain network. 
     Node  9  is added to the blockchain network as a full node during the generation of block  501 . That is, Node  9  stores an entire copy of blocks  1  to  500 , but participates in the Encoding and hashing process with other blockchain nodes of the blockchain network since the generation of block  501 . 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Block IDs 
                 Redundancy Rate 
                 Fault Tolerance 
               
               
                   
                   
               
             
            
               
                   
                  1-100 
                 5 + (3 + 1)/3 
                 6/9 
               
               
                   
                 101-200 
                 4 + (4 + 1)/4 
                 5/9 
               
               
                   
                 201-300 
                 3 + (5 + 1)/5 
                 4/9 
               
               
                   
                 301-400 
                 2 + (5 + 2)/5 
                 4/9 
               
               
                   
                 401-500 
                 1 + (6 + 2)/6 
                 3/9 
               
               
                   
                   
               
            
           
         
       
     
     Table 1 shows the redundancy rate and fault tolerance of blocks  1 - 500  under the blockchain network with nine blockchain nodes according to the above example  600 . Nodes  1 ,  2 ,  3 , and  4  store datasets divided from ECC encoded blocks  1  to  100 . Nodes  5 ,  6 ,  7 ,  8 , and  9  store the original blocks  1  to  100 . Since the code rate for encoding blocks  1  to  100  is 3/4, nodes  1 ,  2 ,  3 , and  4  store 4/3 copies of the original blocks. Nodes  5 ,  6 ,  7 ,  8 , and  9  each stores one copy of the original blocks. Therefore, the redundancy rate of storing blocks  1  to  100  is 5+4/3. The fault tolerance is the proportion of faulty blockchain nodes that can be tolerated by the blockchain network. Since nodes  5 ,  6 ,  7 ,  8 , and  9  store the original blocks  1  to  100 , as long as any one of them is an honest blockchain node, it can provide the original blocks to other blockchain nodes of the blockchain network. If nodes  5 ,  6 ,  7 ,  8 , and  9  are all faulty blockchain nodes, three of nodes  1 ,  2 ,  3 , and  4  that store the datasets need to be honest nodes for recovering a copy of the original blocks. Therefore, a maximum of 6 out of the 9 blockchain nodes can be faulty blockchain nodes. The fault tolerance is 2/3. 
     For blocks  101  to  200 , nodes  1 ,  2 ,  3 ,  4 , and  5  store datasets divided from ECC encoded blocks  101  to  200 . Nodes  6 ,  7 ,  8 , and  9  store the original blocks. Since the code rate for encoding blocks  101  to  200  is 4/5, nodes  1 ,  2 ,  3 ,  4 , and  5  store 5/4 copies of the original blocks. Nodes  6 ,  7 ,  8 , and  9  each stores one copy of the original blocks. Therefore, the redundancy rate of storing blocks  101  to  200  is 4+5/4. A maximum of 5 out of the 9 blockchain nodes can be faulty blockchain nodes. The fault tolerance is 5/9. 
     For blocks  201  to  300 , nodes  1 ,  2 ,  3 ,  4 ,  5 , and  6  store datasets divided from ECC encoded blocks  201  to  300 . Nodes  7 ,  8 , and  9  store the original blocks. Since the code rate for encoding blocks  201  to  300  is 2/3, nodes  1 ,  2 ,  3 ,  4 ,  5 , and  6  store 6/5 copies of the original blocks. Nodes  7 ,  8 , and  9  each stores one copy of the original blocks. Therefore, the redundancy rate of storing blocks  201  to  300  is 3+6/5. A maximum of 4 out of the 9 blockchain nodes can be faulty blockchain nodes. The fault tolerance is 4/9. 
     For blocks  301  to  400 , nodes  1 ,  2 ,  3 ,  4 ,  5 ,  6 , and  7  store datasets divided from ECC encoded blocks  301  to  400 . Nodes  8 , and  9  store the original blocks. Since the code rate for encoding blocks  301  to  400  is 5/7, nodes  1 ,  2 ,  3 ,  4 ,  5 ,  6  and  7  store 7/5 copies of the original blocks. Nodes  8 , and  9  each stores one copy of the original blocks. Therefore, the redundancy rate of storing blocks  301  to  400  is 2+7/5. A maximum of 4 out of the 9 blockchain nodes can be faulty blockchain nodes. The fault tolerance is 4/9. 
     For blocks  401  to  500 , nodes  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 , and  8  store datasets divided from ECC encoded blocks  301  to  400 . Node  9  stores the original blocks. Since the code rate for encoding blocks  401  to  500  is 3/4, nodes  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7  and  8  store 4/3 copies of the original blocks. Node  9  stores one copy of the original blocks. Therefore, the redundancy rate of storing blocks  401  to  500  is 1+7/5. A maximum of 3 out of the 9 blockchain nodes can be faulty blockchain nodes. The fault tolerance is 1/3. 
     If the blockchain nodes agree to reperform ECC encoding to blocks  1  to  500 , since the maximum number of faulty blockchain nodes tolerable by the blockchain network of 9 blockchain nodes is 2, the maximum code rate of the ECC is 7/9. After performing the Encoding and hashing process, the fault tolerance is reduced to 2/9. On the other hand, the redundancy rate is reduced to 9/7, which is significantly lower than the redundancy rates before reperforming the process. Therefore, reperforming the Encoding and hashing process when original blocks are stored in at least one blockchain node effectively reduces redundancy rate and storage consumption of the system. 
     In some cases, a blockchain node may determine that the blockchain data it stores exceeds a predetermined data volume threshold. In such cases, the blockchain node can initiate a request to other blockchain nodes for reperforming the Encoding and hashing process to one or more blocks in order to reduce redundancy rate of the blockchain network. In some cases, the request for reperforming the Encoding and hashing process can be initiated by a trusted node outside of the blockchain network, such as in response to determining that the redundancy rate of the blockchain network is greater than a predetermined threshold. For example, for a blockchain network with nine blockchain nodes as depicted in the example  600 , the minimum redundancy rate under PBFT protocol is 9/7. The trusted node can initiate the request when the redundancy rate of the one or more blocks are over 2. In some embodiments, the blocks can be selected to reperforming the Encoding and hashing process based on their redundancy rate. The blocks with higher redundancy rate can be selected with higher priority due to larger savings on storage. 
     The request for reperforming the Encoding and hashing process can include a maximum code rate for performing the ECC that accounts for the maximum number of faulty blockchain nodes tolerable (i.e., f/(3f+1)). The request can also include instructions of dividing each encoded block of the one or more encoded blocks to a plurality of datasets and assigning the plurality of datasets to the blockchain nodes of the blockchain network. For example, the instructions can instruct each encoded block to be divided to nine datasets, each dataset to be assigned to one of the nine blockchain nodes. In some cases, the instructions are provided by the data storage scheme as discussed in the descriptions of  FIGS. 3 to 5 . 
     If the request is initiated by a blockchain node, the blockchain network can go through the three-phase process (pre-prepare, prepare, and commit phases) of a PBFT algorithm to reach consensus of reperforming ECC according to the instructions included in the request. The blockchain node initiating the request can act as a primary blockchain node for performing the PBFT algorithm. Any blockchain node receiving the request can identify and retrieve the one or more blocks from the primary blockchain node. 
     The blockchain nodes can also directly reperform the ECC according to the instructions if the request is received from the trusted node with proof of authority. In such case, the request can also include identifications identifying at least one blockchain node that stores the one or more blocks. The blockchain node receiving the request can then identify the at least one blockchain node of the blockchain network that stores the one or more blocks based on the request and retrieve the one or more blocks from one of the at least one blockchain node. 
     To retrieve the one or more blocks, the blockchain node can send hash values of the one or more blocks to one of the at least one blockchain node. In some examples, the hash values are stored in block headers of the blockchain. After receiving the one or more blocks, the blockchain node can determine whether the received one or more blocks are authenticate by comparing hash values of the received one or more blocks with corresponding hash values it sent. If the hash values are the same, the received one or more blocks can be determined as authentic. Otherwise, the blockchain node can report the blockchain node that the one or more blocks are received from as faulty node. 
     The blockchain node can then perform ECC of the one or more blocks based on the code rate provided in the request to generate one or more encoded blocks. In the example illustrated in  FIG. 6 , for each encoded block of the one or more encoded blocks, the blockchain node can divide the encoded block into nine datasets according to the instructions and store at least one of nine datasets assigned to the blockchain node according to the instructions. The blockchain nodes can then hash the remaining eight of the plurality of datasets to generate hash values corresponding to remaining eight datasets, store the hash values, and delete the one or more blocks. Afterwards, the Encoding and hashing process for the one or more blocks is then completed. 
     After the Encoding and hashing process is completed for all available blocks, if the redundancy rate of the blockchain network still exceeds a predetermined data storage threshold or the storage consumption of a blockchain node is greater than a predetermined data storage threshold, the blockchain node can notify other blockchain nodes to trigger another round of Encoding and hashing process in response to new blockchain nodes that are added to the blockchain network. For example, if eight blockchain nodes perform the Encoding and hashing process to blocks  1  to  400  before node  9  is added, and the storage consumption of a blockchain node is still greater than 90% of node  8 &#39;s storage capacity, node  8  can send a notification to nodes  1  to  7  to perform another round of Encoding and hashing process to blocks that have been generated after node  8  is added. 
       FIG. 7  depicts an example of a process  700  that can be executed in accordance with embodiments of this specification. For convenience, the process  700  will be described as being performed by a blockchain node. The blockchain node can be a computer or a system of one or more computers, located in one or more locations, and programmed appropriately in accordance with this specification. For example, a blockchain node can be a computing device in a computing system, e.g., the computing system  106 ,  108  of  FIG. 1 , appropriately programmed, can perform the process  700 . 
     At  702 , a blockchain node receives a request for performing ECC to one or more blocks of a blockchain. In some cases, the request includes the code rate and instructions to divide each encoded block of the one or more encoded blocks to a plurality of datasets and to assign the plurality of datasets to the blockchain nodes of the blockchain network. 
     At  704 , the blockchain node obtains the one or more blocks based on blockchain data received from at least one blockchain node of the blockchain network. In some cases, the blockchain data received from the at least one blockchain node are a plurality of datasets divided from an ECC encoded version of the one or more blocks, and the blockchain node obtains the one or more blocks by, identifying one or more datasets divided from the ECC encoded version of the one or more blocks that are stored locally in the blockchain node, and decoding the one or more blocks based on the one or more datasets that are stored locally and the plurality of datasets received from the at least one blockchain node. 
     In some cases, the at least one blockchain node is at least one full blockchain node, and the blockchain node obtains the one or more blocks by retrieving the one or more blocks from the at least one full blockchain node. 
     At  706 , the blockchain node performs ECC of the one or more blocks to generate one or more encoded blocks, wherein a code rate of the one or more encoded blocks equals a minimum number of honest blockchain nodes required by the blockchain network and a total number of blockchain nodes of the blockchain network. 
     In some cases, the one or more blocks are first one or more blocks, and retrieving the first one or more blocks further comprises: sending hash values of the first one or more blocks to the at least one full blockchain node, receiving second one or more blocks from the at least one full blockchain node, and determining the second one or more blocks are authentic if hash values of the second one or more blocks are same as hash values of the first one or more blocks. 
     In some cases, for each encoded block of the one or more encoded blocks, the blockchain node can further divide the encoded block into the plurality of datasets according to the instructions, and store at least one of the plurality of datasets assigned to the blockchain node according to the instructions. 
     In some cases, the blockchain node can further hash a remainder of the plurality of datasets other than the at least one of the plurality of datasets assigned to the blockchain node to generate hash values corresponding to the remainder of the plurality of datasets, store the hash values, and delete the one or more blocks and the remainder of the plurality of datasets. 
     In some cases, the request is a first request and the one or more encoded blocks are first one or more encoded blocks, the blockchain node can further: receive a second request for performing ECC to the one or more blocks of a blockchain in response to a new blockchain node storing the one or more blocks being added to the blockchain network, retrieve the one or more blocks from the new blockchain node, and perform ECC of the one or more blocks to generate second one or more encoded blocks, wherein a code rate of the second one or more encoded blocks equals a minimum number of honest blockchain nodes required by the blockchain network and a total number of blockchain nodes after the new blockchain node is added. 
     In some cases, the new blockchain nodes are full nodes that store a copy of the blockchain. In some cases, the ECC is performed when utilization rate of computational resource of the blockchain node is less than or equal to a predetermined value. In some cases, the ECC is erasure coding performed by adding redundant bits to the one or more blocks. 
       FIG. 8  is a diagram of an example of modules of an apparatus  800  in accordance with embodiments of this specification. The apparatus  800  can be an example of an embodiment of a blockchain node configured to storing and processing blockchain data. The apparatus  800  can correspond to the embodiments described above, and the apparatus  800  includes the following: a receiving module  802  that receives a request for performing ECC to one or more blocks of a blockchain, an obtaining module  804  that obtains the one or more blocks based on blockchain data received from at least one blockchain node of the blockchain network, and an encoding module  806  that performs ECC of the one or more blocks to generate one or more encoded blocks, wherein a code rate of the one or more encoded blocks equals a minimum number of honest blockchain nodes required by the blockchain network and a total number of blockchain nodes of the blockchain network. 
     In some embodiments, the blockchain data received from the at least one blockchain node are a plurality of datasets divided from an ECC encoded version of the one or more blocks, and the obtaining module  804  further performs: identifying one or more datasets divided from the ECC encoded version of the one or more blocks that are stored locally in the blockchain node, and decoding the one or more blocks based on the one or more datasets that are stored locally and the plurality of datasets received from the at least one blockchain node. 
     In some embodiments, the at least one blockchain node is at least one full blockchain node, and the obtaining module further performs retrieving the one or more blocks from the at least one full blockchain node. 
     In some embodiments, the one or more blocks are first one or more blocks, and retrieving the first one or more blocks further comprises: sending hash values of the first one or more blocks to the at least one full blockchain node, receiving second one or more blocks from the at least one full blockchain node, and determining the second one or more blocks are authentic if hash values of the second one or more blocks are same as hash values of the first one or more blocks. 
     In some embodiments, the request includes the code rate and instructions to divide each encoded block of the one or more encoded blocks to a plurality of datasets and to assign the plurality of datasets to the blockchain nodes of the blockchain network. 
     In some embodiments, for each encoded block of the one or more encoded blocks, the apparatus  800  further comprises a division submodule for dividing the encoded block into the plurality of datasets according to the instructions, and a storing submodule for storing at least one of the plurality of datasets assigned to the blockchain node according to the instructions. 
     In some embodiments, the apparatus  800  further comprises a hashing submodule for hashing a remainder of the plurality of datasets other than the at least one of the plurality of datasets assigned to the blockchain node to generate hash values corresponding to the remainder of the plurality of datasets, the storing submodule for storing the hash values, and a deleting submodule to delete the one or more blocks and the remainder of the plurality of datasets. 
     In some embodiments, the request is a first request and the one or more encoded blocks are first one or more encoded blocks, the receiving submodule  802  further receives a second request for performing ECC to the one or more blocks of a blockchain in response to a new blockchain node storing the one or more blocks being added to the blockchain network, the retrieving submodule further retrieves the one or more blocks from the new blockchain node, and the encoding module  806  further performs ECC of the one or more blocks to generate second one or more encoded blocks, wherein a code rate of the second one or more encoded blocks equals a minimum number of honest blockchain nodes required by the blockchain network and a total number of blockchain nodes after the new blockchain node is added. 
     In some embodiments, the new blockchain nodes are full nodes that store a copy of the blockchain. In some embodiments, the ECC is performed when utilization rate of computational resource of the blockchain node is less than or equal to a predetermined value. In some embodiments, the ECC is erasure coding performed by adding redundant bits to the one or more blocks. 
     The system, apparatus, module, or unit illustrated in the previous embodiments can be implemented by using a computer chip or an entity, or can be implemented by using a product having a certain function. A typical embodiment device is a computer, and the computer can be a personal computer, a laptop computer, a cellular phone, a camera phone, a smartphone, a personal digital assistant, a media player, a navigation device, an email receiving and sending device, a game console, a tablet computer, a wearable device, or any combination of these devices. 
     For an embodiment process of functions and roles of each module in the apparatus, references can be made to an embodiment process of corresponding steps in the previous method. Details are omitted here for simplicity. 
     Because an apparatus embodiment basically corresponds to a method embodiment, for related parts, references can be made to related descriptions in the method embodiment. The previously described apparatus embodiment is merely an example. The modules described as separate parts may or may not be physically separate, and parts displayed as modules may or may not be physical modules, may be located in one position, or may be distributed on a number of network modules. Some or all of the modules can be selected based on actual demands to achieve the objectives of the solutions of the specification. A person of ordinary skill in the art can understand and implement the embodiments of the present application without creative efforts. 
     Referring again to  FIG. 8 , it can be interpreted as illustrating an internal functional module and a structure of a blockchain node. An execution body in essence can be an electronic device, and the electronic device includes the following: one or more processors, and one or more computer-readable memories configured to store an executable instruction of the one or more processors. In some embodiments, the one or more computer-readable memories are coupled to the one or more processors and have programming instructions stored thereon that are executable by the one or more processors to perform algorithms, methods, functions, processes, flows, and procedures as described in this specification. This specification also provides one or more non-transitory computer-readable storage media coupled to one or more processors and having instructions stored thereon which, when executed by the one or more processors, cause the one or more processors to perform operations in accordance with embodiments of the methods provided herein. 
     This specification further provides a system for implementing the methods provided herein. The system includes one or more processors, and a computer-readable storage medium coupled to the one or more processors having instructions stored thereon which, when executed by the one or more processors, cause the one or more processors to perform operations in accordance with embodiments of the methods provided herein. 
     Embodiments of the subject matter and the actions and operations described in this specification can be implemented in digital electronic circuitry, in tangibly-embodied computer software or firmware, in computer hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Embodiments of the subject matter described in this specification can be implemented as one or more computer programs, e.g., one or more modules of computer program instructions, encoded on a computer program carrier, for execution by, or to control the operation of, data processing apparatus. For example, a computer program carrier can include one or more computer-readable storage media that have instructions encoded or stored thereon. The carrier may be a tangible non-transitory computer-readable medium, such as a magnetic, magneto optical, or optical disk, a solid state drive, a random access memory (RAM), a read-only memory (ROM), or other types of media. Alternatively, or in addition, the carrier may be an artificially generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. The computer storage medium can be or be part of a machine-readable storage device, a machine-readable storage substrate, a random or serial access memory device, or a combination of one or more of them. A computer storage medium is not a propagated signal. 
     A computer program, which may also be referred to or described as a program, software, a software application, an app, a module, a software module, an engine, a script, or code, can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages; and it can be deployed in any form, including as a stand-alone program or as a module, component, engine, subroutine, or other unit suitable for executing in a computing environment, which environment may include one or more computers interconnected by a data communication network in one or more locations. 
     A computer program may, but need not, correspond to a file in a file system. A computer program can be stored in a portion of a file that holds other programs or data, e.g., one or more scripts stored in a markup language document, in a single file dedicated to the program in question, or in multiple coordinated files, e.g., files that store one or more modules, sub programs, or portions of code. 
     Processors for execution of a computer program include, by way of example, both general- and special-purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive the instructions of the computer program for execution as well as data from a non-transitory computer-readable medium coupled to the processor. 
     The term “data processing apparatus” encompasses all kinds of apparatuses, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. Data processing apparatus can include special-purpose logic circuitry, e.g., an FPGA (field programmable gate array), an ASIC (application specific integrated circuit), or a GPU (graphics processing unit). The apparatus can also include, in addition to hardware, code that creates an execution environment for computer programs, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. 
     The processes and logic flows described in this specification can be performed by one or more computers or processors executing one or more computer programs to perform operations by operating on input data and generating output. The processes and logic flows can also be performed by special-purpose logic circuitry, e.g., an FPGA, an ASIC, or a GPU, or by a combination of special-purpose logic circuitry and one or more programmed computers. 
     Computers suitable for the execution of a computer program can be based on general or special-purpose microprocessors or both, or any other kind of central processing unit. Generally, a central processing unit will receive instructions and data from a read only memory or a random access memory or both. Elements of a computer can include a central processing unit for executing instructions and one or more memory devices for storing instructions and data. The central processing unit and the memory can be supplemented by, or incorporated in, special-purpose logic circuitry. 
     Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to one or more storage devices. The storage devices can be, for example, magnetic, magneto optical, or optical disks, solid state drives, or any other type of non-transitory, computer-readable media. However, a computer need not have such devices. Thus, a computer may be coupled to one or more storage devices, such as, one or more memories, that are local and/or remote. For example, a computer can include one or more local memories that are integral components of the computer, or the computer can be coupled to one or more remote memories that are in a cloud network. Moreover, a computer can be embedded in another device, e.g., a mobile telephone, a personal digital assistant (PDA), a mobile audio or video player, a game console, a Global Positioning System (GPS) receiver, or a portable storage device, e.g., a universal serial bus (USB) flash drive, to name just a few. 
     Components can be “coupled to” each other by being commutatively such as electrically or optically connected to one another, either directly or via one or more intermediate components. Components can also be “coupled to” each other if one of the components is integrated into the other. For example, a storage component that is integrated into a processor (e.g., an L2 cache component) is “coupled to” the processor. 
     To provide for interaction with a user, embodiments of the subject matter described in this specification can be implemented on, or configured to communicate with, a computer having a display device, e.g., a LCD (liquid crystal display) monitor, for displaying information to the user, and an input device by which the user can provide input to the computer, e.g., a keyboard and a pointing device, e.g., a mouse, a trackball or touchpad. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. In addition, a computer can interact with a user by sending documents to and receiving documents from a device that is used by the user; for example, by sending web pages to a web browser on a user&#39;s device in response to requests received from the web browser, or by interacting with an app running on a user device, e.g., a smartphone or electronic tablet. Also, a computer can interact with a user by sending text messages or other forms of message to a personal device, e.g., a smartphone that is running a messaging application, and receiving responsive messages from the user in return. 
     This specification uses the term “configured to” in connection with systems, apparatus, and computer program components. For a system of one or more computers to be configured to perform particular operations or actions means that the system has installed on it software, firmware, hardware, or a combination of them that in operation cause the system to perform the operations or actions. For one or more computer programs to be configured to perform particular operations or actions means that the one or more programs include instructions that, when executed by data processing apparatus, cause the apparatus to perform the operations or actions. For special-purpose logic circuitry to be configured to perform particular operations or actions means that the circuitry has electronic logic that performs the operations or actions. 
     While this specification contains many specific embodiment details, these should not be construed as limitations on the scope of what is being claimed, which is defined by the claims themselves, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be realized in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiments can also be realized in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially be claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claim may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings and recited in the claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system modules and components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     Particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some cases, multitasking and parallel processing may be advantageous.