Major Description
In order to be able to generate many ids in bulk (for example in map reduce jobs) we need a way to generate or reserve large sets of ids. We also need to mix ids reserved with incrementally generated ids from other clients.
For this we need to atomically increment the sequence and return the value it had when the increment happened.
If we're OK to throw the current cached set of values away we can do
NEXT VALUE FOR <seq>(,<N>), that needs to increment value and return the value it incremented from (i.e. it has to throw the current cache away, and return the next value it found at the server).
Or we can invent a new syntax RESERVE VALUES FOR <seq>, <N> that does the same, but does not invalidate the cache.
Note that in either case we won't retrieve the reserved set of values via NEXT VALUE FOR because we'd need to be idempotent in our case, all we need to guarantee is that after a call to RESERVE VALUES FOR <seq>, <N>, which returns a value <M> is that the range [M, M+N) won't be used by any other user of the sequence. My might need reserve 1bn ids this way ahead of a map reduce run.
Any better ideas?