ClickHouse/dbms/include/DB/DataStreams/MergeSortingBlockInputStream.h

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#pragma once
#include <queue>
#include <Poco/TemporaryFile.h>
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#include <common/logger_useful.h>
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#include <DB/Core/SortDescription.h>
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#include <DB/DataStreams/IProfilingBlockInputStream.h>
#include <DB/DataStreams/NativeBlockInputStream.h>
#include <DB/IO/ReadBufferFromFile.h>
#include <DB/IO/CompressedReadBuffer.h>
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namespace DB
{
/** Merges stream of sorted each-separately blocks to sorted as-a-whole stream of blocks.
* If data to sort is too much, could use external sorting, with temporary files.
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*/
/** Part of implementation. Merging array of ready (already read from somewhere) blocks.
* Returns result of merge as stream of blocks, not more than 'max_merged_block_size' rows in each.
*/
class MergeSortingBlocksBlockInputStream : public IProfilingBlockInputStream
{
public:
/// limit - if not 0, allowed to return just first 'limit' rows in sorted order.
MergeSortingBlocksBlockInputStream(Blocks & blocks_, SortDescription & description_,
size_t max_merged_block_size_, size_t limit_ = 0);
String getName() const override { return "MergeSortingBlocks"; }
String getID() const override { return getName(); }
protected:
Block readImpl() override;
private:
Blocks & blocks;
SortDescription description;
size_t max_merged_block_size;
size_t limit;
size_t total_merged_rows = 0;
using CursorImpls = std::vector<SortCursorImpl>;
CursorImpls cursors;
bool has_collation = false;
std::priority_queue<SortCursor> queue;
std::priority_queue<SortCursorWithCollation> queue_with_collation;
/** Two different cursors are supported - with and without Collation.
* Templates are used (instead of virtual functions in SortCursor) for zero-overhead.
*/
template <typename TSortCursor>
Block mergeImpl(std::priority_queue<TSortCursor> & queue);
};
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class MergeSortingBlockInputStream : public IProfilingBlockInputStream
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{
public:
/// limit - if not 0, allowed to return just first 'limit' rows in sorted order.
MergeSortingBlockInputStream(BlockInputStreamPtr input_, SortDescription & description_,
size_t max_merged_block_size_, size_t limit_,
size_t max_bytes_before_external_sort_, const std::string & tmp_path_)
: description(description_), max_merged_block_size(max_merged_block_size_), limit(limit_),
max_bytes_before_external_sort(max_bytes_before_external_sort_), tmp_path(tmp_path_)
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{
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children.push_back(input_);
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}
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String getName() const override { return "MergeSorting"; }
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String getID() const override
{
std::stringstream res;
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res << "MergeSorting(" << children.back()->getID();
for (size_t i = 0; i < description.size(); ++i)
res << ", " << description[i].getID();
res << ")";
return res.str();
}
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protected:
Block readImpl() override;
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private:
SortDescription description;
size_t max_merged_block_size;
size_t limit;
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size_t max_bytes_before_external_sort;
const std::string tmp_path;
Logger * log = &Logger::get("MergeSortingBlockInputStream");
Blocks blocks;
size_t sum_bytes_in_blocks = 0;
std::unique_ptr<IBlockInputStream> impl;
/// Before operation, will remove constant columns from blocks. And after, place constant columns back.
/// (to avoid excessive virtual function calls and because constants cannot be serialized in Native format for temporary files)
/// Save original block structure here.
Block sample_block;
/// Everything below is for external sorting.
std::vector<std::unique_ptr<Poco::TemporaryFile>> temporary_files;
/// For reading data from temporary file.
struct TemporaryFileStream
{
ReadBufferFromFile file_in;
CompressedReadBuffer compressed_in;
BlockInputStreamPtr block_in;
TemporaryFileStream(const std::string & path)
: file_in(path), compressed_in(file_in), block_in(std::make_shared<NativeBlockInputStream>(compressed_in)) {}
};
std::vector<std::unique_ptr<TemporaryFileStream>> temporary_inputs;
BlockInputStreams inputs_to_merge;
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};
}