On Mac OSX, unity will get slower and slower when building a large number of AssetBundles

my unity version is 2018.4.0f1

my project has about 8k assetbundles. when i start a clean build, unity will get slower and slower, it will take more than 10 hours to finish the building.

however, if i restart unity when it gets slowly, it will be fast again, then get slower like before.

at the very begining after restart, it can build about 8 assetbundles per second, after about 30 minutes, it can only build 1 assetbundle with 5 seconds!!!

this problem does not exist on windows.