ClickHouse/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>
#include <Disks/IDisk.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 final : public ext::shared_ptr_helper<StorageLog>, public IStorage
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{
friend class LogSource;
friend class LogBlockOutputStream;
friend struct ext::shared_ptr_helper<StorageLog>;
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public:
String getName() const override { return "Log"; }
Pipes read(
const Names & column_names,
const StorageMetadataPtr & metadata_snapshot,
const SelectQueryInfo & query_info,
const Context & context,
QueryProcessingStage::Enum processed_stage,
size_t max_block_size,
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unsigned num_streams) override;
BlockOutputStreamPtr write(const ASTPtr & query, const StorageMetadataPtr & /*metadata_snapshot*/, const Context & context) override;
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void rename(const String & new_path_to_table_data, const StorageID & new_table_id) override;
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CheckResults checkData(const ASTPtr & /* query */, const Context & /* context */) override;
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void truncate(const ASTPtr &, const StorageMetadataPtr & metadata_snapshot, const Context &, TableExclusiveLockHolder &) override;
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Strings getDataPaths() const override { return {DB::fullPath(disk, table_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(
DiskPtr disk_,
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const std::string & relative_path_,
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const StorageID & table_id_,
const ColumnsDescription & columns_,
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const ConstraintsDescription & constraints_,
bool attach,
size_t max_compress_block_size_);
private:
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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.
size_t offset; /// The offset in compressed file.
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};
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;
String data_file_path;
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Marks marks;
};
using Files = std::map<String, ColumnData>; /// file name -> column data
DiskPtr disk;
String table_path;
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mutable std::shared_mutex rwlock;
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Files files;
Names column_names_by_idx; /// column_index -> name
String marks_file_path;
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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();
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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 StorageMetadataPtr & metadata_snapshot) const;
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};
}