"Classic" Excel (XLS) has a magic limit of 65535 rows per worksheet. This was fixed in XLSX but the version used by the Spreadsheet gem Show archive.org snapshot can only write XLS files.

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If you want to write more data, consider hacking around it using in_groups_of and writing multiple column sets of your data (i.e. split 1 block of 3 columns and 100000 rows into 4 blocks of 3 (12 in total) columns and 25000 rows).

You can do this until you reach the other limit of 256 columns. After that, open up a new workbook or consider a better file type.

As an alternative, you could switch to axlsx, which supports writing XLSX files -- and does that really fast, too.