ClickHouse/src/Storages/MergeTree/IMergeTreeReader.h

86 lines
3.2 KiB
C++

#pragma once
#include <Core/NamesAndTypes.h>
#include <Storages/MergeTree/MergeTreeReaderStream.h>
#include <Storages/MergeTree/MergeTreeBlockReadUtils.h>
namespace DB
{
class IDataType;
/// Reads the data between pairs of marks in the same part. When reading consecutive ranges, avoids unnecessary seeks.
/// When ranges are almost consecutive, seeks are fast because they are performed inside the buffer.
/// Avoids loading the marks file if it is not needed (e.g. when reading the whole part).
class IMergeTreeReader : private boost::noncopyable
{
public:
using ValueSizeMap = std::map<std::string, double>;
using DeserializeBinaryBulkStateMap = std::map<std::string, IDataType::DeserializeBinaryBulkStatePtr>;
IMergeTreeReader(const MergeTreeData::DataPartPtr & data_part_,
const NamesAndTypesList & columns_,
UncompressedCache * uncompressed_cache_,
MarkCache * mark_cache_,
const MarkRanges & all_mark_ranges_,
const MergeTreeReaderSettings & settings_,
const ValueSizeMap & avg_value_size_hints_ = ValueSizeMap{});
/// Return the number of rows has been read or zero if there is no columns to read.
/// If continue_reading is true, continue reading from last state, otherwise seek to from_mark
virtual size_t readRows(size_t from_mark, bool continue_reading, size_t max_rows_to_read, Columns & res_columns) = 0;
virtual bool canReadIncompleteGranules() const = 0;
virtual ~IMergeTreeReader();
const ValueSizeMap & getAvgValueSizeHints() const;
/// Add columns from ordered_names that are not present in the block.
/// Missing columns are added in the order specified by ordered_names.
/// num_rows is needed in case if all res_columns are nullptr.
void fillMissingColumns(Columns & res_columns, bool & should_evaluate_missing_defaults, size_t num_rows);
/// Evaluate defaulted columns if necessary.
void evaluateMissingDefaults(Block additional_columns, Columns & res_columns);
/// If part metadata is not equal to storage metadata, than
/// try to perform conversions of columns.
void performRequiredConversions(Columns & res_columns);
const NamesAndTypesList & getColumns() const { return columns; }
size_t numColumnsInResult() const { return columns.size(); }
size_t getFirstMarkToRead() const
{
return all_mark_ranges.front().begin;
}
MergeTreeData::DataPartPtr data_part;
protected:
/// avg_value_size_hints are used to reduce the number of reallocations when creating columns of variable size.
ValueSizeMap avg_value_size_hints;
/// Stores states for IDataType::deserializeBinaryBulk
DeserializeBinaryBulkStateMap deserialize_binary_bulk_state_map;
/// Columns that are read.
NamesAndTypesList columns;
std::unordered_map<String, DataTypePtr> columns_from_part;
UncompressedCache * uncompressed_cache;
MarkCache * mark_cache;
MergeTreeReaderSettings settings;
const MergeTreeData & storage;
MarkRanges all_mark_ranges;
friend class MergeTreeRangeReader::DelayedStream;
/// Alter conversions, which must be applied on fly if required
MergeTreeData::AlterConversions alter_conversions;
};
}