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99 lines
3.8 KiB
C++
99 lines
3.8 KiB
C++
#pragma once
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#include <Core/NamesAndTypes.h>
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#include <Storages/MergeTree/MergeTreeReaderStream.h>
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#include <port/clock.h>
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namespace DB
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{
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class IDataType;
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/// Reads the data between pairs of marks in the same part. When reading consecutive ranges, avoids unnecessary seeks.
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/// When ranges are almost consecutive, seeks are fast because they are performed inside the buffer.
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/// Avoids loading the marks file if it is not needed (e.g. when reading the whole part).
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class MergeTreeReader : private boost::noncopyable
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{
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public:
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using ValueSizeMap = std::map<std::string, double>;
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using DeserializeBinaryBulkStateMap = std::map<std::string, IDataType::DeserializeBinaryBulkStatePtr>;
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MergeTreeReader(String path_, /// Path to the directory containing the part
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MergeTreeData::DataPartPtr data_part_,
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NamesAndTypesList columns_,
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UncompressedCache * uncompressed_cache_,
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MarkCache * mark_cache_,
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bool save_marks_in_cache_,
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const MergeTreeData & storage_,
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MarkRanges all_mark_ranges_,
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size_t aio_threshold_,
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size_t max_read_buffer_size_,
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ValueSizeMap avg_value_size_hints_ = ValueSizeMap{},
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const ReadBufferFromFileBase::ProfileCallback & profile_callback_ = ReadBufferFromFileBase::ProfileCallback{},
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clockid_t clock_type_ = CLOCK_MONOTONIC_COARSE);
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~MergeTreeReader();
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const ValueSizeMap & getAvgValueSizeHints() const;
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/// Add columns from ordered_names that are not present in the block.
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/// Missing columns are added in the order specified by ordered_names.
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/// num_rows is needed in case if all res_columns are nullptr.
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void fillMissingColumns(Columns & res_columns, bool & should_evaluate_missing_defaults, size_t num_rows);
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/// Evaluate defaulted columns if necessary.
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void evaluateMissingDefaults(Block additional_columns, Columns & res_columns);
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const NamesAndTypesList & getColumns() const { return columns; }
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size_t numColumnsInResult() const { return columns.size(); }
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/// Return the number of rows has been read or zero if there is no columns to read.
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/// If continue_reading is true, continue reading from last state, otherwise seek to from_mark.
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/// Fills res_columns in order specified in getColumns() list. If column was not read it will be nullptr.
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size_t readRows(size_t from_mark, bool continue_reading, size_t max_rows_to_read, Columns & res_columns);
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MergeTreeData::DataPartPtr data_part;
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size_t getFirstMarkToRead() const
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{
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return all_mark_ranges.back().begin;
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}
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private:
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using FileStreams = std::map<std::string, std::unique_ptr<MergeTreeReaderStream>>;
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/// avg_value_size_hints are used to reduce the number of reallocations when creating columns of variable size.
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ValueSizeMap avg_value_size_hints;
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/// Stores states for IDataType::deserializeBinaryBulk
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DeserializeBinaryBulkStateMap deserialize_binary_bulk_state_map;
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/// Path to the directory containing the part
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String path;
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FileStreams streams;
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/// Columns that are read.
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NamesAndTypesList columns;
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UncompressedCache * uncompressed_cache;
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MarkCache * mark_cache;
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/// If save_marks_in_cache is false, then, if marks are not in cache, we will load them but won't save in the cache, to avoid evicting other data.
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bool save_marks_in_cache;
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const MergeTreeData & storage;
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MarkRanges all_mark_ranges;
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size_t aio_threshold;
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size_t max_read_buffer_size;
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void addStreams(const String & name, const IDataType & type,
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const ReadBufferFromFileBase::ProfileCallback & profile_callback, clockid_t clock_type);
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void readData(
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const String & name, const IDataType & type, IColumn & column,
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size_t from_mark, bool continue_reading, size_t max_rows_to_read,
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bool read_offsets = true);
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friend class MergeTreeRangeReader::DelayedStream;
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};
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}
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