VidCache.cache was a []VidInfo indexed directly by volume id, so caching
one volume with a large id grew the backing array to that many entries
(each 48 bytes), allocating a zeroed slot for every unused id below it. A
single id of 32M cost ~1.5GB resident, plus geometric realloc churn as the
append loop doubled the array.
Use map[uint32]VidInfo so memory scales with the number of volumes actually
cached rather than the largest id seen. Parse ids with ParseUint(.,32) so
values outside the uint32 volume-id range are rejected instead of silently
wrapping into a key.
Chris Lu
058569c77b