db: add statistics about queued reads
db: add statistics about queued reads

scylladb/scylla,scylladb/scylla,raphaelsc/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,avikivity/scylla,duarten/scylla,raphaelsc/scylla,avikivity/scylla,kjniemi/scylla,kjniemi/scylla,scylladb/scylla,raphaelsc/scylla,kjniemi/scylla,avikivity/scylla