Go stores a map value inline once it fits in 128 bytes, and indirectly above
that. Shrinking storage.VolumeInfo to 120 bytes therefore moved 1.6M of them
into the map's own slots, which are allocated to capacity rather than to
occupancy, and the map grew by 149MB even though each volume got smaller.
Hold pointers, so the size of a volume record stops deciding how it is stored.
Updates are written through the pointer already there, so a heartbeat that
changes a volume allocates nothing, as it did when the struct was above the
threshold and Go was doing this itself.
At 800k volume ids across 3 servers the resident topology goes from 705.3MB to
546.6MB, with heartbeat cost unchanged at 111.6MB.
Chris LuandGitHub
5e9b7833ee