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