hbase源码系列（十二）Get、Scan在服务端是如何处理？

　　　　　　if (!done) {
              long maxResultSize = scanner.getMaxResultSize();
              if (maxResultSize <= 0) {
                maxResultSize = maxScannerResultSize;
              }
              List<Cell> values = new ArrayList<Cell>();
              MultiVersionConsistencyControl.setThreadReadPoint(scanner.getMvccReadPoint());
              region.startRegionOperation(Operation.SCAN);
              try {
                int i = 0;
                synchronized(scanner) {
                  for (; i < rows && currentScanResultSize < maxResultSize; i++) {
                    // 它用的是这个nextRaw方法
                    boolean moreRows = scanner.nextRaw(values);
                    if (!values.isEmpty()) {
                       results.add(Result.create(values));
                    }
                    if (!moreRows) {
                      break;
                    }
                    values.clear();
                  }
                }
              } finally {
                region.closeRegionOperation();
              }
            }

            // 没找到设置moreResults为false，找到了把结果添加到builder里面去
            if (scanner.isFilterDone() && results.isEmpty()) {
              moreResults = false;
              results = null;
            } else {
              addResults(builder, results, controller);
            }
          } 
        }

/**  把查询出来的结果保存到results当中  */
    private boolean nextInternal(List<Cell> results, int limit)
    throws IOException {

      while (true) {
        //从storeHeap里面取出一个来
        KeyValue current = this.storeHeap.peek();

        byte[] currentRow = null;
        int offset = 0;
        short length = 0;
        if (current != null) {
          currentRow = current.getBuffer();
          offset = current.getRowOffset();
          length = current.getRowLength();
        }
        //检查一下到这个row是否应该停止了
        boolean stopRow = isStopRow(currentRow, offset, length);
        if (joinedContinuationRow == null) {
          // 如果要停止了，就用filter的filterRowCells过滤一下results.
          if (stopRow) {
            if (filter != null && filter.hasFilterRow()) {
              //使用filter过滤掉一些cells
              filter.filterRowCells(results);
            }
            return false;
          }
          // 如果有filter的话，过滤通过
          if (filterRowKey(currentRow, offset, length)) {
            boolean moreRows = nextRow(currentRow, offset, length);
            if (!moreRows) return false;
            results.clear();
            continue;
          }
          //把结果保存到results当中
          KeyValue nextKv = populateResult(results, this.storeHeap, limit, currentRow, offset,
              length);
          // Ok, we are good, let‘s try to get some results from the main heap.
          // 在populateResult找到了足够limit数量的
          if (nextKv == KV_LIMIT) {
            if (this.filter != null && filter.hasFilterRow()) {
              throw new IncompatibleFilterException(
                "Filter whose hasFilterRow() returns true is incompatible with scan with limit!");
            }
            return true; // We hit the limit.
          }
          
          stopRow = nextKv == null ||
              isStopRow(nextKv.getBuffer(), nextKv.getRowOffset(), nextKv.getRowLength());
          // save that the row was empty before filters applied to it.
          final boolean isEmptyRow = results.isEmpty();

          // We have the part of the row necessary for filtering (all of it, usually).
          // First filter with the filterRow(List). 过滤一下刚才找出来的
          if (filter != null && filter.hasFilterRow()) {
            filter.filterRowCells(results);
          }
          //如果result的空的，啥也没找到，这是。。。悲剧啊
          if (isEmptyRow) {
            boolean moreRows = nextRow(currentRow, offset, length);
            if (!moreRows) return false;
            results.clear();
            // This row was totally filtered out, if this is NOT the last row,
            // we should continue on. Otherwise, nothing else to do.
            if (!stopRow) continue;
            return false;
          }

          // Ok, we are done with storeHeap for this row.
          // Now we may need to fetch additional, non-essential data into row.
          // These values are not needed for filter to work, so we postpone their
          // fetch to (possibly) reduce amount of data loads from disk.
          if (this.joinedHeap != null) {
            KeyValue nextJoinedKv = joinedHeap.peek();
            // If joinedHeap is pointing to some other row, try to seek to a correct one.
            boolean mayHaveData =
              (nextJoinedKv != null && nextJoinedKv.matchingRow(currentRow, offset, length))
              || (this.joinedHeap.requestSeek(KeyValue.createFirstOnRow(currentRow, offset, length),
                true, true)
                && joinedHeap.peek() != null
                && joinedHeap.peek().matchingRow(currentRow, offset, length));
            if (mayHaveData) {
              joinedContinuationRow = current;
              populateFromJoinedHeap(results, limit);
            }
          }
        } else {
          // Populating from the joined heap was stopped by limits, populate some more.
          populateFromJoinedHeap(results, limit);
        }

        // We may have just called populateFromJoinedMap and hit the limits. If that is
        // the case, we need to call it again on the next next() invocation.
        if (joinedContinuationRow != null) {
          return true;
        }

        // Finally, we are done with both joinedHeap and storeHeap.
        // Double check to prevent empty rows from appearing in result. It could be
        // the case when SingleColumnValueExcludeFilter is used.
        if (results.isEmpty()) {
          boolean moreRows = nextRow(currentRow, offset, length);
          if (!moreRows) return false;
          if (!stopRow) continue;
        }

        // We are done. Return the result.
        return !stopRow;
      }
    }

public StoreScanner(Store store, ScanInfo scanInfo, Scan scan, final NavigableSet<byte[]> columns) throws IOException {

    matcher = new ScanQueryMatcher(scan, scanInfo, columns,
        ScanType.USER_SCAN, Long.MAX_VALUE, HConstants.LATEST_TIMESTAMP,
        oldestUnexpiredTS);

    // 返回MemStore、所有StoreFile的Scanner.
    List<KeyValueScanner> scanners = getScannersNoCompaction();

    //explicitColumnQuery:是否过滤列族 lazySeekEnabledGlobally默认是true 如果文件数量超过1个，isParallelSeekEnabled就是true
    if (explicitColumnQuery && lazySeekEnabledGlobally) {
      for (KeyValueScanner scanner : scanners) {
        scanner.requestSeek(matcher.getStartKey(), false, true);
      }
    } else {
      if (!isParallelSeekEnabled) {
        for (KeyValueScanner scanner : scanners) {
          scanner.seek(matcher.getStartKey());
        }
      } else {
　　　　　//一般走这里，并行查
        parallelSeek(scanners, matcher.getStartKey());
      }
    }

    // 一个堆里面包括了两个scanner，MemStore、StoreFile的Scanner
    heap = new KeyValueHeap(scanners, store.getComparator());

    this.store.addChangedReaderObserver(this);
  }

public DeleteResult isDeleted(byte [] buffer, int qualifierOffset,
      int qualifierLength, long timestamp) {
    //时间戳小于删除列族的时间戳，说明这个列族被删掉是后来的事情
    if (hasFamilyStamp && timestamp <= familyStamp) {
      return DeleteResult.FAMILY_DELETED;
    }
    //检查时间戳
    if (familyVersionStamps.contains(Long.valueOf(timestamp))) {
        return DeleteResult.FAMILY_VERSION_DELETED;
    }

    if (deleteBuffer != null) {
　　   
      int ret = Bytes.compareTo(deleteBuffer, deleteOffset, deleteLength,
          buffer, qualifierOffset, qualifierLength);

      if (ret == 0) {
        if (deleteType == KeyValue.Type.DeleteColumn.getCode()) {
          return DeleteResult.COLUMN_DELETED;
        }
        // 坑爹的Delete它只删除相同时间戳的，遇到不想的它就pass了
        if (timestamp == deleteTimestamp) {
          return DeleteResult.VERSION_DELETED;
        }

        //时间戳不对，这个Delete失效了
        deleteBuffer = null;
      } else if(ret < 0){
        // row比当前的大，这个Delete也失效了
        deleteBuffer = null;
      } else {
        throw new IllegalStateException(...);
      }
    }

    return DeleteResult.NOT_DELETED;