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73 lines
2.5 KiB
C++
73 lines
2.5 KiB
C++
#pragma once
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#include <Processors/IProcessor.h>
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#include <Processors/RowsBeforeLimitCounter.h>
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#include <Core/SortDescription.h>
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namespace DB
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{
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/// Implementation for LIMIT N OFFSET M
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/// This processor support multiple inputs and outputs (the same number).
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/// Each pair of input and output port works independently.
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/// The reason to have multiple ports is to be able to stop all sources when limit is reached, in a query like:
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/// SELECT * FROM system.numbers_mt WHERE number = 1000000 LIMIT 1
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///
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/// always_read_till_end - read all data from input ports even if limit was reached.
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/// with_ties, description - implementation of LIMIT WITH TIES. It works only for single port.
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class LimitTransform : public IProcessor
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{
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private:
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UInt64 limit;
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UInt64 offset;
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bool always_read_till_end;
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bool with_ties;
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const SortDescription description;
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Chunk previous_row_chunk; /// for WITH TIES, contains only sort columns
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std::vector<size_t> sort_column_positions;
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UInt64 rows_read = 0; /// including the last read block
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RowsBeforeLimitCounterPtr rows_before_limit_at_least;
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/// State of port's pair.
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/// Chunks from different port pairs are not mixed for better cache locality.
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struct PortsData
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{
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Chunk current_chunk;
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InputPort * input_port = nullptr;
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OutputPort * output_port = nullptr;
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bool is_finished = false;
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};
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std::vector<PortsData> ports_data;
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size_t num_finished_port_pairs = 0;
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Chunk makeChunkWithPreviousRow(const Chunk & current_chunk, UInt64 row_num) const;
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ColumnRawPtrs extractSortColumns(const Columns & columns) const;
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bool sortColumnsEqualAt(const ColumnRawPtrs & current_chunk_sort_columns, UInt64 current_chunk_row_num) const;
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public:
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LimitTransform(
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const Block & header_, UInt64 limit_, UInt64 offset_, size_t num_streams = 1,
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bool always_read_till_end_ = false, bool with_ties_ = false,
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SortDescription description_ = {});
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String getName() const override { return "Limit"; }
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Status prepare(const PortNumbers & /*updated_input_ports*/, const PortNumbers & /*updated_output_ports*/) override;
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Status prepare() override; /// Compatibility for TreeExecutor.
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Status preparePair(PortsData & data);
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void splitChunk(PortsData & data);
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InputPort & getInputPort() { return inputs.front(); }
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OutputPort & getOutputPort() { return outputs.front(); }
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void setRowsBeforeLimitCounter(RowsBeforeLimitCounterPtr counter) { rows_before_limit_at_least.swap(counter); }
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};
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}
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