Convert attachment 124272 [details], a 2.2 MB file from bug 99238 to XLSX, eg. using --convert to: soffice.exe --convert-to xlsx testcase_file.ods => Resulting XLSX is 347 MB. Observed with LO Version: 25.8.0.0.alpha0+ (7f8a5594694c5f2861648c36ff7c87a21422f283) and LO 7.4.0.3 / Windows. Between LO 7.1.0.3 and 7.3.0.3, the XLSX is only 30 MB. Between LO 6.3.0.4 and 7.0.0.3: 44 MB. With LO 6.2.0.3: 30 MB. Between LO 5.4.0.3 and 6.1.0.3: 25 MB. Between LO 4.0.0.3 and 5.3.0.3: 2 MB. It would at least be interesting to find the change in 7.4 and 5.4 that is responsible for the most notable size increases.
With 24.8, save as XLSX results in such 354 MB. Opening this XLSX with Excel and resaving, result in 393 MB Opening the ODS with Excel saved as XLSX, result in 192 MB. Opening this XLSX with Calc resaved as XLSX, result in 29 MB. I wasn't able to clean the format for all sheets for AA1:XFD1048576, because LO hangs after select the range for all sheets.
The change in 5.4 resulting in 2 MB -> 25 MB size increase is the following: https://cgit.freedesktop.org/libreoffice/core/commit/?id=1cde2eb9d128c9b1b658b1380074461429ab2214 author Justin Luth <justin_luth@sil.org> 2017-02-10 12:44:47 +0300 committer Bartosz Kosiorek <gang65@poczta.onet.pl> 2017-02-14 01:14:28 +0000 tdf#105840 EXCEL export: fixes for hidden defaultRow
bibisected with win64-7.4 first bad commit source 4c5f8ccf0a2320432b8fe91add1dcadf54d9fd58