Review / Recommendations for hbase writer code

ted_yu is graciously reviewing the hbase writer related code and has some recommendations. (more to come as review progresses). I will keep track of those in this jira and perhaps spin off other jira(s) depending on the scope of changes.

For FlowRunCoprocessor.java :

• private HRegion region;
  Try to declare as Region - the interface. This way, you are to call methods that are stable across future releases.

• private long getCellTimestamp(long timestamp, List<Tag> tags) { tags is not used, remove the parameter. For FlowScanner: - private final InternalScanner flowRunScanner; Currently InternalScanner is Private. If you must use it, try surfacing your case to hbase so that it can be marked: @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC) @InterfaceStability.Evolving w.r.t. regionScanner : {code}

  if (internalScanner instanceof RegionScanner)

  { this.regionScanner = (RegionScanner) internalScanner; }

  I see IllegalStateException being thrown in some methods when regionScanner is null. Better bail out early in the ctor.
  
  
  

  public static AggregationOperation getAggregationOperationFromTagsList(
  List<Tag> tags) {
  for (AggregationOperation aggOp : AggregationOperation.values()) {
  for (Tag tag : tags) {
  if (tag.getType() == aggOp.getTagType())

  { return aggOp; {code}

The above nested loop can be improved (a lot):

values() returns an array. If you pre-generate a Set (https://docs.oracle.com/javase/7/docs/api/java/util/EnumSet.html) containing all the values, the outer loop can be omitted.
You iterate through tags and see if tag.getType() is in the Set.