don't query cassandra for more data then we need
don't query cassandra for more data then we need

when to < oldestchunk.t0, the memory server says oldest is whatever the
oldest is in mem, but we don't need to query cassandra until that time range!

replay/metrictank,raintank/metrictank,raintank/metrictank,OOM-Killer/metrictank,OOM-Killer/metrictank,raintank/raintank-metric,OOM-Killer/metrictank,raintank/raintank-metric,replay/metrictank,replay/metrictank,raintank/metrictank,raintank/raintank-metric,replay/metrictank,raintank/metrictank