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#pragma once
#include <IO/ReadBuffer.h>
#include <Common/PODArray.h>
#include <Processors/Merges/Algorithms/IMergingAlgorithm.h>
#include <Processors/Merges/IMergingTransform.h>
namespace Poco { class Logger; }
namespace DB
{
/// Tiny struct, stores number of a Part from which current row was fetched, and insertion flag.
struct RowSourcePart
{
UInt8 data = 0;
RowSourcePart() = default;
explicit RowSourcePart(size_t source_num, bool skip_flag = false)
{
static_assert(sizeof(*this) == 1, "Size of RowSourcePart is too big due to compiler settings");
setSourceNum(source_num);
setSkipFlag(skip_flag);
}
size_t getSourceNum() const { return data & MASK_NUMBER; }
/// In CollapsingMergeTree case flag means "skip this rows"
bool getSkipFlag() const { return (data & MASK_FLAG) != 0; }
void setSourceNum(size_t source_num)
{
data = (data & MASK_FLAG) | (static_cast<UInt8>(source_num) & MASK_NUMBER);
}
void setSkipFlag(bool flag)
{
data = flag ? data | MASK_FLAG : data & ~MASK_FLAG;
}
static constexpr size_t MAX_PARTS = 0x7F;
static constexpr UInt8 MASK_NUMBER = 0x7F;
static constexpr UInt8 MASK_FLAG = 0x80;
};
using MergedRowSources = PODArray<RowSourcePart>;
/** Gather single stream from multiple streams according to streams mask.
* Stream mask maps row number to index of source stream.
* Streams should contain exactly one column.
*/
class ColumnGathererStream final : public IMergingAlgorithm
{
public:
ColumnGathererStream(size_t num_inputs, ReadBuffer & row_sources_buf_, size_t block_preferred_size_ = DEFAULT_BLOCK_SIZE);
void initialize(Inputs inputs) override;
void consume(Input & input, size_t source_num) override;
Status merge() override;
/// for use in implementations of IColumn::gather()
template <typename Column>
void gather(Column & column_res);
UInt64 getMergedRows() const { return merged_rows; }
UInt64 getMergedBytes() const { return merged_bytes; }
private:
/// Cache required fields
struct Source
{
ColumnPtr column;
size_t pos = 0;
size_t size = 0;
void update(ColumnPtr column_)
{
column = std::move(column_);
size = column->size();
pos = 0;
}
};
MutableColumnPtr result_column;
std::vector<Source> sources;
ReadBuffer & row_sources_buf;
const size_t block_preferred_size;
Source * source_to_fully_copy = nullptr;
ssize_t next_required_source = -1;
size_t cur_block_preferred_size = 0;
UInt64 merged_rows = 0;
UInt64 merged_bytes = 0;
};
class ColumnGathererTransform final : public IMergingTransform<ColumnGathererStream>
{
public:
ColumnGathererTransform(
const Block & header,
size_t num_inputs,
ReadBuffer & row_sources_buf_,
size_t block_preferred_size_ = DEFAULT_BLOCK_SIZE);
String getName() const override { return "ColumnGathererTransform"; }
void work() override;
protected:
void onFinish() override;
UInt64 elapsed_ns = 0;
Poco::Logger * log;
};
template <typename Column>
void ColumnGathererStream::gather(Column & column_res)
{
row_sources_buf.nextIfAtEnd();
RowSourcePart * row_source_pos = reinterpret_cast<RowSourcePart *>(row_sources_buf.position());
RowSourcePart * row_sources_end = reinterpret_cast<RowSourcePart *>(row_sources_buf.buffer().end());
if (next_required_source == -1)
{
/// Start new column.
cur_block_preferred_size = std::min(static_cast<size_t>(row_sources_end - row_source_pos), block_preferred_size);
column_res.reserve(cur_block_preferred_size);
}
size_t cur_size = column_res.size();
next_required_source = -1;
while (row_source_pos < row_sources_end && cur_size < cur_block_preferred_size)
{
RowSourcePart row_source = *row_source_pos;
size_t source_num = row_source.getSourceNum();
Source & source = sources[source_num];
bool source_skip = row_source.getSkipFlag();
if (source.pos >= source.size) /// Fetch new block from source_num part
{
next_required_source = source_num;
return;
}
++row_source_pos;
/// Consecutive optimization. TODO: precompute lengths
size_t len = 1;
size_t max_len = std::min(static_cast<size_t>(row_sources_end - row_source_pos), source.size - source.pos); // interval should be in the same block
while (len < max_len && row_source_pos->data == row_source.data)
{
++len;
++row_source_pos;
}
row_sources_buf.position() = reinterpret_cast<char *>(row_source_pos);
if (!source_skip)
{
/// Whole block could be produced via copying pointer from current block
if (source.pos == 0 && source.size == len)
{
/// If current block already contains data, return it.
/// Whole column from current source will be returned on next read() iteration.
source_to_fully_copy = &source;
return;
}
else if (len == 1)
column_res.insertFrom(*source.column, source.pos);
else
column_res.insertRangeFrom(*source.column, source.pos, len);
cur_size += len;
}
source.pos += len;
}
}
}
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