Compression in MongoDb 3.2 does not work

I installed MongoDb 3.2, and configured snappy compression in mongodb configuration file: engine: wiredTiger wiredTiger: engineConfig: cacheSizeGB: 99 journalCompressor: none collectionConfig: blockCompressor: snappy indexConfig: prefixCompression: true However I do not think compression actually work as I could see average object size in the collection is about the same (I filled collection created from scratch by the same objects right after configuration change and service restart): MMAPv1 no-compression avgObjSize: 5kb WiredTiger snappy avgObjSize: 4kb WiredTiger zlib avgObjSize: 4kb when I run stats on collection here is what I see for "snappy": "compression" : { "compressed pages read" : NumberInt(0), "compressed pages written" : NumberInt(5), "page written failed to compress" : NumberInt(0), "page written was too small to compress" : NumberInt(4), "raw compression call failed, additional data available" : NumberInt(0), "raw compression call failed, no additional data available" : NumberInt(0), "raw compression call succeeded" : NumberInt(0) }, for zlib: { "compressed pages read" : NumberInt(0), "compressed pages written" : NumberInt(1), "page written failed to compress" : NumberInt(0), "page written was too small to compress" : NumberInt(3), "raw compression call failed, additional data available" : NumberInt(0), "raw compression call failed, no additional data available" : NumberInt(1), "raw compression call succeeded" : NumberInt(2) } Not sure how to read this info, and not sure how can I detect what's wrong with compression. I should also say I had only few (like 10) objects in each scenario. Would it be enough to accurately measure average object compression ratio? **UPDATE:** with 1188 documents mongodb ver3 shown around 50% better compression ratio comparing to mongodb ver2.6 (MMAPv1), however got no difference between snappy and zlib: dataSize and avgObjSize are the same for some reason. When I request statistics it shown WiredTiger:creationString:...block_compressor=zlib.. for the first database and block_compressor=snappy for the second one, so databases and collections seemed to be created with right compression algorithms