public void mergeRegions()

in hbase-tools/src/main/java/org/apache/hbase/RegionsMerger.java [177:254]
71 lines of code
11 McCabe index (conditional complexity)

  public void mergeRegions(String tblName, int targetRegions) throws Exception {
    TableName table = TableName.valueOf(tblName);
    Path tableDir = getTablePath(table);
    try(Connection conn = ConnectionFactory.createConnection(conf)) {
      Admin admin = conn.getAdmin();
      LongAdder counter = new LongAdder();
      LongAdder lastTimeProgessed = new LongAdder();
      //need to get all regions for the table, regardless of region state
      List<RegionInfo> regions = admin.getRegions(table);
      Map<Future, Pair<RegionInfo, RegionInfo>> regionsMerging = new ConcurrentHashMap<>();
      long roundsNoProgress = 0;
      while (regions.size() > targetRegions) {
        LOG.info("Iteration: {}", counter);
        RegionInfo previous = null;
        int regionSize = regions.size();
        LOG.info("Attempting to merge {} regions to reach the target {} ...", regionSize,
            targetRegions);
        //to request merge, regions must be OPEN, though
        regions = getOpenRegions(conn, table);
        for (RegionInfo current : regions) {
          if (!current.isSplit()) {
            if (previous != null &&
                canMerge(tableDir, previous, current,regionsMerging.values())) {
              //Before submitting a merge request, we need to check if any of the region candidates
              //still have merge references from previous cycle
              boolean hasMergeRef =
                hasPreviousMergeRef(conn, previous) || hasPreviousMergeRef(conn, current);
              if(!hasMergeRef) {
                Future f = admin.mergeRegionsAsync(current.getEncodedNameAsBytes(),
                  previous.getEncodedNameAsBytes(), true);
                Pair<RegionInfo, RegionInfo> regionPair = new Pair<>(previous, current);
                regionsMerging.put(f, regionPair);
                if ((regionSize - regionsMerging.size()) <= targetRegions) {
                  break;
                }
              } else {
                LOG.info("Skipping merge of candidates {} and {} because of existing merge "
                  + "qualifiers.", previous.getEncodedName(), current.getEncodedName());
              }
              previous = null;
            } else {
              previous = current;
            }
          }
          else{
            LOG.debug("Skipping split region: {}", current.getEncodedName());
          }
        }
        counter.increment();
        LOG.info("Sleeping for {} seconds before next iteration...", (sleepBetweenCycles/1000));
        Thread.sleep(sleepBetweenCycles);
        regionsMerging.forEach((f, currentPair)-> {
          if (f.isDone()) {
            LOG.info("Merged regions {} and {} together.",
              currentPair.getFirst().getEncodedName(),
              currentPair.getSecond().getEncodedName());
            regionsMerging.remove(f);
            lastTimeProgessed.reset();
            lastTimeProgessed.add(counter.longValue());
          } else {
            LOG.warn("Merge of regions {} and {} isn't completed yet.",
              currentPair.getFirst(),
              currentPair.getSecond());
          }
        });
        roundsNoProgress = counter.longValue() - lastTimeProgessed.longValue();
        if(roundsNoProgress == this.maxRoundsStuck){
          LOG.warn("Reached {} iterations without progressing with new merges. Aborting...",
            roundsNoProgress);
          break;
        }

        //again, get all regions, regardless of the state,
        // in order to avoid breaking the loop prematurely
        regions = admin.getRegions(table);
      }
    }
  }