Apply a WAL to Reconstruct State

Problem A page is reconstructed from a write-ahead log. Given a base page and a list of WAL records, apply them in LSN (log sequence number) order to reconstruct the current page; support point-in-time recovery by stopping at a target LSN.

Input / Output

• Input: a base page and an ordered list of WAL records (insert/update/delete), each with an LSN; optionally a target LSN.
• Output: the reconstructed page after applying records up to (and including) the target LSN.

Constraints

• Records must be applied strictly in LSN order.
• Support stopping at an arbitrary LSN for time-travel / PITR.

Example

• base + [insert, update, delete] in LSN order → current page; stop early at an LSN → a historical page.