Each specific sample file is a hashed collection, where the key is the PC offset from the transient data, and the value is the number of samples recorded against that offset. The files are mmap()ed into the daemon's memory space. The code to actually log the write against the sample file can be found in libdb/.

For recording stack traces, we have a more complicated sample filename mangling scheme that allows us to identify cross-binary calls. We use the same sample file format, where the key is a 64-bit value composed from the from,to pair of offsets.