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116 lines
2.8 KiB
C++
116 lines
2.8 KiB
C++
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#include <DB/DataStreams/MergeSortingBlockInputStream.h>
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namespace DB
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{
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Block MergeSortingBlockInputStream::read()
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{
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/** На данный момент - очень простой алгоритм:
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* - прочитать в оперативку все блоки;
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* - объединять по два соседних блока;
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*/
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typedef std::list<Block> Blocks;
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Blocks blocks;
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while (Block block = input->read())
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blocks.push_back(block);
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if (blocks.empty())
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return Block();
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while (blocks.size() > 1)
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{
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for (Blocks::iterator it = blocks.begin(); it != blocks.end();)
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{
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Blocks::iterator next = it;
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++next;
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if (next == blocks.end())
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break;
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merge(*it, *next);
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++it;
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blocks.erase(it++);
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}
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}
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return blocks.front();
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}
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void MergeSortingBlockInputStream::merge(Block & left, Block & right)
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{
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Block merged;
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size_t left_size = left.rows();
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size_t right_size = right.rows();
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size_t left_pos = 0;
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size_t right_pos = 0;
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typedef std::vector<const IColumn *> ConstColumns;
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typedef std::vector<IColumn *> Columns;
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/// Все столбцы блоков.
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ConstColumns left_columns;
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ConstColumns right_columns;
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Columns merged_columns;
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/// Столбцы, по которым идёт сортировка.
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ConstColumns left_sort_columns;
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ConstColumns right_sort_columns;
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size_t num_columns = left.columns();
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for (size_t i = 0; i < num_columns; ++i)
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{
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ColumnWithNameAndType col;
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col.name = left.getByPosition(i).name;
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col.type = left.getByPosition(i).type;
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col.column = left.getByPosition(i).column->cloneEmpty();
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merged.insert(col);
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merged_columns.push_back(&*col.column);
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left_columns.push_back(&*left.getByPosition(i).column);
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right_columns.push_back(&*right.getByPosition(i).column);
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}
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for (size_t i = 0, size = description.size(); i < size; ++i)
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{
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left_sort_columns.push_back(&*left.getByPosition(description[i].column_number).column);
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right_sort_columns.push_back(&*right.getByPosition(description[i].column_number).column);
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}
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/// Объединяем.
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while (right_pos < right_size || left_pos < left_size)
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{
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/// Откуда брать строку - из левого или из правого блока?
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int res = 0;
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if (right_pos == right_size)
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res = -1;
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else if (left_pos == left_size)
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res = 1;
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else
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for (size_t i = 0, size = description.size(); i < size; ++i)
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if ((res = description[i].direction * left_sort_columns[i]->compareAt(left_pos, right_pos, *right_sort_columns[i])))
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break;
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/// Вставляем строку в объединённый блок.
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if (res <= 0)
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{
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for (size_t i = 0; i < num_columns; ++i)
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merged_columns[i]->insert((*left_columns[i])[left_pos]);
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++left_pos;
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}
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else
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{
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for (size_t i = 0; i < num_columns; ++i)
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merged_columns[i]->insert((*right_columns[i])[right_pos]);
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++right_pos;
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}
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}
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left = merged;
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}
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}
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