Ternary tree enhanced append-only skip list: A high-performance blockchain data search index

Information stored via blockchain’s incremental method enforces data immutability on distributed computer storage. However, storing data incrementally in blocks introduces a temporal constraint, namely, a linear time cost to search for historical blockchain data. Indexing computer data is a well-known technique to quicken retrieval times, with successful blockchain-specific techniques being derived from the skip list data structure, because redundant and obsolete index fragments are not stored. However, upon evaluation of these append-only deterministic skip list indexes, it is evident that a most recent version bias is introduced. Once again, it impairs the retrieval of historical blockchain data. To address this problem, we introduce the Ternary Tree Enhanced Append-only Skip List (TEASL) index. This composite index exploits the known inverse relationship between a binary tree and a deterministic skip list and extends this relationship to utilise a ternary tree. Empirical analysis and comparison of existing indexing techniques demonstrates enhanced search query traversal performance, regardless of where the data is located in the blockchain. Furthermore, TEASL does not introduce any additional storage cost. The TEASL indexing technique is proven to be the fastest append-only skip list-based indexing technique for blockchain. The code supporting this indexing technique is publicly available on GitHub https://github.com/jarednewell/TEASL/ . • TEASL’s transformational algorithm constructs a ternary tree search index from an append-only skip list, elaborating on the known inverse relationship between a binary tree and a deterministic skip list and applies it to a ternary search tree. • The ternary tree is constructed from the append-only skip list data structure sequentially and in real-time with blockchain block updates. Moreover, no index data duplication exists. That is, all previously constructed updates are required to form a complete index. • The TEASL index has superior search traversal performance which is 85.71 % faster than the current fastest append-only skip list indexing technique for blockchain and is equally as storage-efficient. TEASL has more constant blockchain data retrieval times while adapting by remaining optimal and current as the blockchain increases in size. • TEASL is suitable for a distributed client-server model which is blockchain. In this distributed configuration, index traversal occurs in two steps: First, the local ternary tree in the TEASL index is accessed on the client device, thus reducing the search space size. Second, data is retrieved from the blockchain server via the EASL index, refined by the results of the ternary tree. This reduces the cost of data retrieval via the network. • The TEASL construction algorithm allows the granularity of the ternary tree to be increased or reduced, allowing a trade-off between TEASL’s query performance times and the storage performance. This allows for the adaptation to different resource-constrained client devices, such as IoT hardware types.