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Chris LuandGitHub
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* wdclient: age vid map entries by generation instead of chaining snapshots The vid map kept its history as a linked list of past snapshots, trimmed in place by storing nil into a node's cache pointer. That cost up to six full copies of the volume-location map, a recursive walk taking a different lock per level, and deletes that had to cascade through every generation. It also had to special-case explicitly-empty entries, or fallback would resurrect locations a newer snapshot had cleared. Keep one map instead, and stamp each entry with the generation it was learned in. resetVidMap bumps the generation and drops entries that were not relearned within the retained window, which is the same retention the chain provided: an entry survives DefaultVidMapCacheSize resets. The first write of a generation replaces an entry rather than merging into it, so a volume that moved answers with where it is now — the property a fresh map per reset used to give for free. Entries are copy-on-write, so locations handed to a caller are no longer shifted underneath it by a concurrent delete. The map is never swapped now, so the client-side lock and its stable / current accessors go away with it. * wdclient: make vid map entries immutable and drop them once emptied Review follow-up. Updating an entry in place left the copy-on-write guarantee resting on callers never holding the entry pointer; install a new entry instead, so the rule is simply that a stored entry never changes. Deleting a volume's last location now drops the entry rather than keeping an empty one, which a client that never resets would otherwise hold for every volume it ever saw deleted. Lookups already treat an empty entry as a miss, so nothing observable changes. * wdclient: let the newest generation decide between regular and EC locations GetLocations checked the regular map first whatever its generation, so a volume that was EC encoded kept answering with the regular copies the previous master knew until they expired — for as long as the retained window, since nothing relearns a copy that no longer exists. The snapshot chain did not have this problem: the newest map was consulted first and only a volume it knew nothing about fell through to older ones. Restore that by comparing generations, with regular copies winning a tie, since a tie means one generation reported both.