Lower Bounds on Retroactive Data Structures

11/26/2022

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by   Lily Chung, et al.

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We prove essentially optimal fine-grained lower bounds on the gap between a data structure and a partially retroactive version of the same data structure. Precisely, assuming any one of three standard conjectures, we describe a problem that has a data structure where operations run in O(T(n,m)) time per operation, but any partially retroactive version of that data structure requires T(n,m) · m^1-o(1) worst-case time per operation, where n is the size of the data structure at any time and m is the number of operations. Any data structure with operations running in O(T(n,m)) time per operation can be converted (via the "rollback method") into a partially retroactive data structure running in O(T(n,m) · m) time per operation, so our lower bound is tight up to an m^o(1) factor common in fine-grained complexity.