How to decompress mongo journal files
There's two forms of Snappy compression, the basic form and the streaming form. The basic form has the limitation that it all must fit in memory, so the streaming form exists to be able to compress larger amounts of data. The streaming format has a header and then subranges that are compressed. If the header is missing, it sounds like maybe you compressed using the basic form and are trying to uncompress with the streaming form. https://github.com/andrix/python-snappy/issues/40
If that is the case, use decompress instead of stream_decompress.
But if could be that the data isn't compressed at all:
with open('journal/WiredTigerLog.0000000011') as f: for line in f: print linecould work.
Minimum log record size for WiredTiger is 128 bytes. If a log record is 128 bytes or smaller, WiredTiger does not compress that record. https://docs.mongodb.com/manual/core/journaling/