[BUG] Slow generation performance

🐛 Bug Report

We are generating an Excel file with lots of rows but minimal formatting. We’ve found that the writeBuffer() call will spend aggregated 20.85s in addStyleModel() and only 5s in addWorksheets().

One of the bottlenecks seem to be using the serialized XML as the key on this.index.style in _addStyle(). We tried passing an Int16Array into the method and keying it on ${style[0]},${style[1]},${style[2]},${style[3]},${style[4]},${style[5]} instead, which reduced it to 17.12s.

We also observed that the style objects for each cell were always a different object, so the weakmap was never used. Combined with removing the weakmap checks, the total aggregate time of addStyleModel() was reduced to 558ms.

Lib version: 4.2.1

[hfhchan]

We reduced it to 2.76s by calling finalizeWorkbook() before calling writeBuffer:

class ExcelGenerator {
  private internStyle<T extends Partial<Excel.Style>>(internedStyles: Map<string, T>, style: T, type: number) {
    let buf = `${JSON.stringify(style)}${type}`;

    const internedStyle = internedStyles.get(buf);
    if (internedStyle) {
      return internedStyle;
    }

    const newInternedStyle = Object.freeze(Object.assign({}, style));
    internedStyles.set(buf, newInternedStyle);
    return newInternedStyle;
  }

  public finalizeWorkbook(workbook: Excel.Workbook) {
    const internedStyles = new Map<string, Partial<Excel.Style>>();
    workbook.worksheets.forEach(worksheet => {
      (worksheet as any)._rows.forEach((row: Excel.Row) => {
        (row as any)._cells.forEach((cell: Excel.Cell) => {
          cell.style = this.internStyle(internedStyles, cell.style, cell.type);
        });
      });
    });
  }
}

[SpectreWulf]

We reduced it to 2.76s by calling finalizeWorkbook() before calling writeBuffer:

class ExcelGenerator {
  private internStyle<T extends Partial<Excel.Style>>(internedStyles: Map<string, T>, style: T, type: number) {
    let buf = `${JSON.stringify(style)}${type}`;

    const internedStyle = internedStyles.get(buf);
    if (internedStyle) {
      return internedStyle;
    }

    const newInternedStyle = Object.freeze(Object.assign({}, style));
    internedStyles.set(buf, newInternedStyle);
    return newInternedStyle;
  }

  public finalizeWorkbook(workbook: Excel.Workbook) {
    const internedStyles = new Map<string, Partial<Excel.Style>>();
    workbook.worksheets.forEach(worksheet => {
      (worksheet as any)._rows.forEach((row: Excel.Row) => {
        (row as any)._cells.forEach((cell: Excel.Cell) => {
          cell.style = this.internStyle(internedStyles, cell.style, cell.type);
        });
      });
    });
  }
}

This literally cut down the writeBuffer() time in our project by nearly 50% (!)

Thanks a lot! ❤