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#pragma once
#include <optional>
#include <Storages/IStorage.h>
namespace DB
{
class Context;
/** Implements a table engine for the system table "numbers".
* The table contains the only column number UInt64.
* From this table, you can read all natural numbers, starting from 0 (to 2^64 - 1, and then again).
*
* You could also specify a limit (how many numbers to give).
* If multithreaded is specified, numbers will be generated in several streams
* (and result could be out of order). If both multithreaded and limit are specified,
* the table could give you not exactly 1..limit range, but some arbitrary 'limit' numbers.
*
* In multithreaded case, if even_distributed is False, implementation with atomic is used,
* and result is always in [0 ... limit - 1] range.
*/
class StorageSystemNumbers final : public IStorage
{
public:
/// If even_distribution is true, numbers are distributed evenly between streams.
/// Otherwise, streams concurrently increment atomic.
StorageSystemNumbers(const StorageID & table_id, bool multithreaded_, std::optional<UInt64> limit_ = std::nullopt, UInt64 offset_ = 0, bool even_distribution_ = true);
std::string getName() const override { return "SystemNumbers"; }
Pipe read(
const Names & column_names,
const StorageSnapshotPtr & storage_snapshot,
SelectQueryInfo & query_info,
ContextPtr context,
QueryProcessingStage::Enum processed_stage,
size_t max_block_size,
size_t num_streams) override;
bool hasEvenlyDistributedRead() const override { return true; }
bool isSystemStorage() const override { return true; }
bool supportsTransactions() const override { return true; }
private:
bool multithreaded;
bool even_distribution;
std::optional<UInt64> limit;
UInt64 offset;
};
}
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