linux - zip -9 compression isn't reducing file size -


i have file want compress zip archive being automatically sent via amazon ses , email rejected due following:

which seems mean email larger 10mb limit. zip archive created using standard level 6 compression, change use maximum compression (level 9) doesn't seem change archive size.

original (level 6) command:

zip standard.zip somefile.txt    adding: somefile.txt (deflated 42%)

attempted (level 9) command:

zip -9 9.zip somefile.txt    adding: somefile.txt (deflated 42%)

results:

-rw-rw-r-- 1 ec2-user ec2-user 5.0m jan 27 23:20 standard.zip -rw-rw-r-- 1 ec2-user ec2-user 5.0m jan 27 23:19 9.zip

as can tell results i'm running on aws ec2 instance amazon linux.

i expected 9.zip archive smaller, doing wrong?

in addition fact performance impacted when changing compression levels not issue use case process.

the file has .zip file, recipient not archive format.

i expected 9.zip archive smaller, doing wrong?

what you're doing wrong expecting maximum level of zlib compression offer significant compression on best medium level. isn't true, can shown empirically. highly compressible data compresses very @ level 6, , non-compressible data doesn't benefit in noticeable manner level 9.

if wanted compress lot use zip tool built against zopfli instead of zlib, expect compression take much, longer.


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