Pinot中的Forward Index源码分析

还是以Quickstart为例，说一下forward index的创建过程。

1. 收集各个column的统计数据

   代码同dictionary index。

2. 再次遍历，按行处理每列的索引

   iterator复位

   // Build the index
   recordReader.rewind();

   重新遍历，对每行索引

   LOGGER.info("Start building IndexCreator!");
   while (recordReader.hasNext()) {
     long start = System.currentTimeMillis();
     GenericRow row = recordReader.next();
     long stop = System.currentTimeMillis();
     indexCreator.indexRow(row);
     long stop1 = System.currentTimeMillis();
     totalRecordReadTime += (stop - start);
     totalIndexTime += (stop1 - stop);
   }

   indexRow的实现：

   @Override
   public void indexRow(GenericRow row) {
       for (final String column : dictionaryCreatorMap.keySet()) {
   
           Object columnValueToIndex = row.getValue(column);
           Object dictionaryIndex;
           if (dictionaryCache.get(column).containsKey(columnValueToIndex)) {
               dictionaryIndex = dictionaryCache.get(column).get(columnValueToIndex