long getScannerVirtualTime(long scannerId) {
    RegionScannerHolder rsh = checkQuotaAndGetRegionScannerContext(scannerId);
    return rsh == null ? 0L : rsh.getNextCallSeq();
  }
Get the vtime associated with the scanner. Currently the vtime is the number of "next" calls.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RSRpcServices.java