add comment about how 4 MB size is arbitrarily chosen as cutoff for mcdb setting POSIX_MADV_RANDOM on the mcdb mmap
add comment about how 4 MB size is arbitrarily chosen as cutoff
for mcdb setting POSIX_MADV_RANDOM on the mcdb mmap


gstrauss/mcdb,gstrauss/mcdb,gstrauss/mcdb,gstrauss/mcdb,gstrauss/mcdb