I am running the iibench for MongoDB on two hosts. Both use the WT b-tree, one with snappy and the other with zlib compression. The test uses 10 threads to load 200M documents per thread. Immediately after the load is done the zlib test uses ~500G versus ~330G for snappy. With some idle time the zlib disk usage drops to ~160G. At first I thought the problem was only for zlib, but watching the size of data/journal during tests shows problems for snappy and zlib.
My test host has 40 hyperthread cores, 144G RAM and fast (PCIe) flash
Can WiredTiger delete log files sooner?
I have a test in progress and it is about 30% done. The problem for the zlib configuration is too much space used in the journal directory. Note that "data" is the root for database files:
And this is from the snappy test at about 20% done:
And this is from later in the snappy test:
And later in the zlib test: