The more code can use GetMany(), the better performance gets on top of
NBS. To this end, add a call to ValueStore that allows code to read
many values concurrently. This can be used e.g. by read-ahead code
that's navigating prolly trees to increase performance.
Fixes#3019
Adds the ability to stream individual chunks requested via GetMany() back to caller.
Removes readAmpThresh and maxReadSize. Lowers the S3ReadBlockSize to 512k.
LocalDatabase generally uses a BatchStoreAdaptor, which is a kinda
dumb wrapper around ChunkStore. During a Pull(), though, this would
cause Chunks to be Put in a top-down fashion, meaning that Chunks
wound up in the backing store _before_ other Chunks that they
reference. This means that LocalDatabases were transiently invalid,
and that cancelling an in-progress pull could lead to an invalid DB.
Now, calling validatingBatchStore() on a LocalDatabase returns a
BatchStore that uses the same strategy as RemoteDatabaseClient,
caching chunks as the come in and putting them into the backing store
bottom-up when Flush() is called.
Fixes#1915
cmasone-attic