ClickHouse/dbms/src/Storages/StorageLog.h

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#pragma once
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#include <map>
#include <shared_mutex>
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#include <ext/shared_ptr_helper.h>
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#include <Poco/File.h>
#include <Storages/IStorage.h>
#include <Common/FileChecker.h>
#include <Common/escapeForFileName.h>
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namespace DB
{
/** Implements simple table engine without support of indices.
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* The data is stored in a compressed form.
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*/
class StorageLog : public ext::shared_ptr_helper<StorageLog>, public IStorage
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{
friend class LogBlockInputStream;
friend class LogBlockOutputStream;
public:
std::string getName() const override { return "Log"; }
std::string getTableName() const override { return name; }
BlockInputStreams read(
const Names & column_names,
const SelectQueryInfo & query_info,
const Context & context,
QueryProcessingStage::Enum processed_stage,
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size_t max_block_size,
unsigned num_streams) override;
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BlockOutputStreamPtr write(const ASTPtr & query, const Settings & settings) override;
void rename(const String & new_path_to_db, const String & new_database_name, const String & new_table_name) override;
bool checkData() const override;
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void truncate(const ASTPtr &) override;
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std::string full_path() const { return path + escapeForFileName(name) + '/';}
String getDataPath() const override { return full_path(); }
protected:
/** Attach the table with the appropriate name, along the appropriate path (with / at the end),
* (the correctness of names and paths is not verified)
* consisting of the specified columns; Create files if they do not exist.
*/
StorageLog(
const std::string & path_,
const std::string & name_,
const ColumnsDescription & columns_,
size_t max_compress_block_size_);
private:
String path;
String name;
mutable std::shared_mutex rwlock;
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/** Offsets to some row number in a file for column in table.
* They are needed so that you can read the data in several threads.
*/
struct Mark
{
size_t rows; /// How many rows are before this offset including the block at this offset.
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size_t offset; /// The offset in compressed file.
};
using Marks = std::vector<Mark>;
/// Column data
struct ColumnData
{
/// Specifies the column number in the marks file.
/// Does not necessarily match the column number among the columns of the table: columns with lengths of arrays are also numbered here.
size_t column_index;
Poco::File data_file;
Marks marks;
};
using Files_t = std::map<String, ColumnData>;
Files_t files; /// name -> data
Names column_names; /// column_index -> name
Poco::File marks_file;
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/// The order of adding files should not change: it corresponds to the order of the columns in the marks file.
void addFiles(const String & column_name, const IDataType & type);
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bool loaded_marks = false;
size_t max_compress_block_size;
size_t file_count = 0;
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FileChecker file_checker;
/// Read marks files if they are not already read.
/// It is done lazily, so that with a large number of tables, the server starts quickly.
/// You can not call with a write locked `rwlock`.
void loadMarks();
/// The order of adding files should not change: it corresponds to the order of the columns in the marks file.
void addFile(const String & column_name, const IDataType & type, size_t level = 0);
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/** For normal columns, the number of rows in the block is specified in the marks.
* For array columns and nested structures, there are more than one group of marks that correspond to different files
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* - for elements (file name.bin) - the total number of array elements in the block is specified,
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* - for array sizes (file name.size0.bin) - the number of rows (the whole arrays themselves) in the block is specified.
*
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* Return the first group of marks that contain the number of rows, but not the internals of the arrays.
*/
const Marks & getMarksWithRealRowCount() const;
std::string getFullPath() const { return path + escapeForFileName(name) + '/'; }
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};
}