NPOI Version Used

Latest master.

File Type

• XLSX
• XLS
• DOCX
• XLSM
• OTHER

Use Case

Faster loading of XLSX files when only reading is required.

Description

When checking load performance for document I realized that that disposing a file caused write operation to it. This is because the default operating mode is Read/Write.

It's not intuitive to find how to open file in read-only mode as requires call to OPCPackage.Open. Testing against large file in benchmark project:

var sw = Stopwatch.StartNew();
var package = OPCPackage.Open(_filePath, PackageAccess.READ);
var workbook = new XSSFWorkbook(package);
workbook.Dispose();
sw.Stop();
Console.WriteLine($"Opening as read: {sw.Elapsed}");

sw = Stopwatch.StartNew();
workbook = new XSSFWorkbook(_filePath);
workbook.Dispose();
sw.Stop();
Console.WriteLine($"Opening as read-write: {sw.Elapsed}");

Opening as read: 00:00:12.4033364
Opening as read-write: 00:00:18.3022784
Opening as read: 00:00:12.7855461
Opening as read-write: 00:00:17.7144075

Would it make sense to expose constructor parameter or options to create XSSFWorkbook in faster read-only mode?