[GitHub] [incubator-doris] imay commented on a change in pull request #2547: [Segment V2] Support lazy materialization read

[GitBox <gi...@apache.org>]

imay commented on a change in pull request #2547: [Segment V2] Support lazy materialization read
URL: https://github.com/apache/incubator-doris/pull/2547#discussion_r361136068
 
 

 ##########
 File path: be/src/olap/rowset/segment_v2/segment_iterator.cpp
 ##########
 @@ -353,31 +418,56 @@ Status SegmentIterator::_seek_columns(const std::vector<ColumnId>& column_ids, r
     return Status::OK();
 }
 
+Status SegmentIterator::_read_columns(const std::vector<ColumnId>& column_ids,
+                                      RowBlockV2* block,
+                                      size_t row_offset,
+                                      size_t nrows) {
+    for (auto cid : column_ids) {
+        auto column_block = block->column_block(cid);
+        ColumnBlockView dst(&column_block, row_offset);
+        size_t rows_read = nrows;
+        RETURN_IF_ERROR(_column_iterators[cid]->next_batch(&rows_read, &dst));
+        block->set_delete_state(column_block.delete_state());
+        DCHECK_EQ(nrows, rows_read);
+    }
+    return Status::OK();
+}
+
 Status SegmentIterator::next_batch(RowBlockV2* block) {
     SCOPED_RAW_TIMER(&_opts.stats->block_load_ns);
     if (UNLIKELY(!_inited)) {
         RETURN_IF_ERROR(_init());
+        if (_lazy_materialization_read) {
+            _block_rowids.reserve(block->capacity());
+        }
         _inited = true;
     }
 
     uint32_t total_read = 0;
     uint32_t remaining = block->capacity();
-    // trying to fill in block
+    _block_rowids.resize(0);
+    const auto& read_columns = _lazy_materialization_read ? _predicate_columns : block->schema()->column_ids();
+
+    // phase 1: read rows selected by various index (indicated by _row_bitmap) into block
+    // when using lazy-materialization-read, only columns with predicates are read
     do {
         uint32_t range_from;
         uint32_t range_to;
         bool has_next_range = _range_iter->next_range(remaining, &range_from, &range_to);
         if (!has_next_range) {
             break;
         }
+        if (_lazy_materialization_read) {
+            for (uint32_t rid = range_from; rid < range_to; rid++) {
+                _block_rowids.push_back(rid);
 
 Review comment:
   If _block_rowids is array, compare operation in push_back can be avoid?

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