How to optimize the performance of large documents?

I'm trying to build a program for Online Excel, but I'm having performance issues. In my implementation, a workbook is a document. The json format of the document is as follows: ```json { "activeSheetId": "aaa", "sheets": { "aaa": { "cells": { "0": { "0": { "value": "123" } } } }, "bbb": { "cells": {} } } } ``` op format is as follows. ``` //set value { type: 'setValue', sheetId: 'aaa', row: 0, col: 0, value: '123' } //add worksheet { type: 'addSheet', sheetId: 'bbb', sheetJson: { cells: {} } } ``` The performance issue is that the workbook's json is so large, and each time applyOp reads the entire workbook's json from the database. I expect each worksheet to be a subdocument, and each applyOp reads only the main document (workbook) and the corresponding subdocument (worksheet) based on op.