It seems that LZMA compressor does ignore advenced option “–compression-extension-file: default_compressed_extensions.txt” and compress already compressed files anyway.
I have a test folder with various .pdf files, I’ve added manually the “.pdf” (but this bug “works” with other default extensions as .mp3) extension to the “default_compressed_extensions.txt” file and run a few tests. Folder size is about 2.75 GB:
zip-compression-method - LZMA - default_compressed_extensions.txt with .pdf - takes about 13min.
zip-compression-method - LZMA - default_compressed_extensions.txt without .pdf - takes about 12min.
zip-compression-method - Deflate - default_compressed_extensions.txt with .pdf - takes about 0:56 sec.
zip-compression-method - Deflate - default_compressed_extensions.txt without .pdf - takes about 2:30 min.
Default “deflate” method correctly process already compressed files (according to “default_compressed_extensions.txt” ) and doesn’t compress them. LZMA mode does ignore these extensions and compress them anyway (thus no difference in profile execution time). I’m using Duplicati version 18.104.22.168_beta_2020-01-18.